management of salt-affected soils in the ncew shemshemia

Management of Salt-affected Soils in the NCEW "Shemshemia" Irrigation Scheme in

the Upper Gash Valley of Eritrea

By Mhereteab Tesfai, Virginia Dawod and Kiflemariam Abreha

March 2002

DCG Report No. 20

Management of Salt-affected Soils in the NCEW ‘Shemshemia’ Irrigation Scheme in the Upper Gash

Valley of Eritrea.

Mehreteab Tesfai, University of Asmara, Eritrea. Virginia Dawod, University of Asmara, Eritrea. Kiflemariam Abreha, Ministry of Agriculture, Eritrea.

Report No. 20 March 2002

The Drylands Coordination Group (DCG) is an NGO-driven forum for exchange of practical experiences and knowledge on food security and natural resource management in the drylands of Africa. DCG facilitates this exchange of experiences between NGOs and research - and policy-making institutions. The DCG activities, which are carried out by DCG members in Ethiopia, Eritrea, Mali and Sudan, aim to contribute to improved food security of vulnerable households and sustainable natural resource management in the drylands of Africa. The founding DCG members consist of ADRA Norway, CARE Norway, Norwegian Church Aid, Norwegian People's Aid, The Stromme Foundation and The Development Fund. Noragric, the Centre for International Environment and Development Studies at the Agricultural University of Norway provides the secretariat as a facilitating and implementing body for the DCG. The DCG’s activities are funded by NORAD (the Norwegian Agency for Development Cooperation). This Report was carried out on behalf of the DCG branch in Eritreaa, which includes the National Confederation for Eritrean Workers, Norwegian Church Aid in Eritrea, Ministry of Agriculture and University of Asmara. Extracts from this publication may only be reproduced after prior consultation with the DCG secretariat. The findings, interpretations and conclusions expressed in this publication are entirely those of the author(s) and cannot be attributed directly to the Drylands Coordination Group.

Tesfai, M., V. Dawod, K. Abresha. Drylands Coordination Group Report No. 20 (March, 2002) Drylands Co-ordination Group P.O. Box 5001 N-1432 Ås Norway Tel.: +47 64 94 98 23 Fax: +47 64 94 07 60 Internet: http://www.drylands-group.org ISSN: 1503-0601 Photo credits: T. A. Benjaminsen, Gry Synnevåg, DCG Eritrea. Cover design: Spekter Reklamebyrå as, Ås Printed at: Rotator, Ås.

Drylands Coordination Group

iii

CONTENTS FOREWORD IV

ACRONYMS V

1. INTRODUCTION 1 1.1. BACKGROUND 1 1.2. JUSTIFICATION 2 1.3. OBJECTIVES OF THE STUDY 4 1.4. TERMS OF REFERENCE 4

2. DESCRIPTION OF THE STUDY AREA 5 2.1 LOCATION & TOPOGRAPHY 5 2.2 POPULATION 6 2.3. CLIMATE 9 2.4. GEOLOGY 10 2.5. HYDROLOGY & DRAINAGE 10 2.6. NATURAL VEGETATION & LAND USE 11

3. METHODS OF STUDY 12 3.1. FIELD SURVEY & MEASUREMENTS 12 3.2. SOIL AND WATER SAMPLING 14 3.3 LABORATORY ANALYSIS OF SOILS & WATER 14

3.4. SOIL CLASSIFICATION & MAPPING METHODS 15 3.5. INTERVIEWS AND GROUP DISCUSSIONS 16

4. FINDINGS & DISCUSSION 16 4.1. THE FARMING SYSTEMS ANALYSIS 16

4.1.1 Historic review of Shemshemia farm 17 4.1.2. Crop production systems 18 4.1.3. Irrigation water quality 21 4.1.4. Production constraints 23 4.2.1. Soil physical properties of the Shemshemia area 25 4.2.2. Soil chemical properties of the Shemshemia area 33

4.3. PROBLEM SOILS IN THE SHEMSHEMIA AREA 43 4.3.1. Characteristics of the sodic soils (black alkaline soils) in Shemshemia 44 4.3.2. Effects of sodicity on soil properties 44 4.3.3. Effects of sodicity on plant growth 45

4.4. RECLAMATION & MANAGEMENT OF THE SODIC SOILS 45 4.4.1. Chemical methods for soil amendments 45 4.4.2. Physical and biological methods for soil amendments 47 4.4.3. Socio-economic considerations 48

4.5. CHECKLIST FOR PREVENTION OF NON-SODIC AREAS 49 5. CONCLUSIONS 49

6. REFERENCES 51

ANNEXES 53 ANNEX A: SOIL PROFILE DESCRIPTIONS 53 ANNEX B: SOIL PHYSICAL AND CHEMICAL DATA 56 ANNEX C. CHECKLIST QUESTIONNAIRE 62

Management of Soil-affected Soils

iv

FOREWORD

Irrigated agriculture is one of the approaches used to increase food production so that

food security can be achieved in the semi-arid and arid regions of the world such as

Eritrea. In Eritrea, there are potential rivers draining into the southwestern lowlands of

the country where extensive flat plains are found, among others, in the area of the

Shemshemia irrigation scheme in the upper Gash valley. A study on the management of

salt affected soils in the Shemshemia irrigation scheme was carried out to determine the

magnitude of salt problems and to propose solutions.

This study report gives an insight into the background of the research project followed

by a description of the study area. Consequently, the methods and approaches used to

probe the problems in the Shemshemia irrigation scheme have been extensively

explained.

The findings of the report review the historical development of the Shemshemia farm

and then describe the crop production, land use types and land coverage in the study

area. Water and soil data collected in the field and in the laboratory are interpreted and

discussed. The possible methods to amend the soil problems (i.e. sodicity) from the

technical as well as the socio-economic point of view are considered and discussed.

Furthermore, a checklist has been prepared for prevention of sodic problems developing

in the currently non-sodic areas in Shemshemia and its vicinity.

The consultant team would like to thank NORAD for financing this research,

NORAGRIC and DCG (Norway) staff for co-ordination. We gratefully acknowledge

also the members of NCEW and DCG (Eritrea) in general and in particular to Mr.

Amanuel Negassi, Mrs. Laraine Black and others for their support in facilitating the

administrative and financial issues related to the research project.

We are indebted to all staff of the soil laboratory of the research department in the MoA

and also to water laboratory staff in the WRD at the MoLWE. Our special thanks goes

to Mr. Tekle Yemane in the WRD, Eritrea for assisting in the production of the digital

land use and soil use maps.

Asmara, March 2002

Salinity/sodicity project team


v

ACRONYMS

CEC Cation Exchange Capacity

DCG Drylands Co-operation Group

DF Development Fund

EC Electrical Conductivity

EPLF Eritrean Peoples’ Liberation Front

ESP Exchangeable Sodium Percentage

FAO Food and Agriculture Organisation of the United Nations

GoE Government of Eritrea

GPS Global Positioning System

GIS Geographic Information System

MoA Ministry of Agriculture

MoLWE Ministry of Land, Water and Environment

MoME Ministry of Mines and Energy

NCEW National Confederation of Eritrean Workers

NPA Norwegians Peoples’ Aid

NORAD Norwegian Agency for Development Co-operation

NORAGRIC Centre for International Environment & Development Studies

PBS Percent Base Saturation

SAR Sodium Adsorption Ratio

SAS Salt Affected Soils

TDS Total Dissolved Solids

ToR Terms of Reference

UoA University of Asmara

WRD Water Resources Department


1

1. INTRODUCTION 1.1. BACKGROUND

Norwegian People’s Aid (NPA) and the Development Fund (DF) have worked with

the National Confederation of Eritrean Workers (NCEW) to develop peasants’ co-

operatives and vocational training in south-western Eritrea for many years. Part of

this co-operation has been the development of the Shemshemia irrigation scheme in

the Gash-Barka region.

The farmers in the Shemshemia area have complained of increasing salinity and/or

sodicity in their fields and requested that the problem required study.

Recommendations on how to rehabilitate those areas already affected, and on how to

apply control measures to prevent further recurrence of salinity and/or sodicity

problems in other uncultivated fields were required. A team of local consultants from

the University of Asmara (UoA) and Ministry of Agriculture (MoA) was put together

to carry out the study.

During a preliminary field visit to the Shemshemia farm in May 2001, the consultant

team observed that poor drainage plus structural degradation of the soils in the

irrigated fields had retarded the growth of citrus plants and reduced crop yields.

Moreover, dark coloured soil surface layers, containing dispersed clay and organic

particles were observed in some parts of uncultivated fields in the form of slick spots.

These are characteristic of sodic soils. It was realised that the main problems in the

area may not be due to salinity but rather to sodicity. Preliminary field samples had

also shown low salinity levels (in most cases) i.e. electrical conductivity (ECe) <1 dS

m-1, and most of the soils measured a pH >8.5. This indicates that the soils have high

sodium content, which has led to structural degradation and poor drainage of applied

irrigation water.

The team prepared a proposal for the study and carried out a detailed field survey and

measurements in September 2001, the results of which are presented in this report,

together with recommendations for correction and prevention of the problem.


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1.2. JUSTIFICATION

Soil is one of the most important natural resources, especially in a country like

Eritrea where agriculture is the main source of income and employment for the

majority of the population (70-80% of its 3.5 million people) (World Bank, 1994).

Nonetheless, information on Eritrean soils in general and salt-affected soils in

particular, is very scarce and lacks ground verification. Eritrean soils are suffering

from various forms of degradation leading to decreasing productivity. Water and

wind erosion are the most severe forms of degradation, but the soils are also

physically degraded through compaction and structural breakdown, biologically

degraded through removal of organic matter, chemically degraded through

continuous removal of nutrients and through development of salt-affected soils

particularly in the more arid areas or areas under irrigation.

Salt-affected soils (SAS) refer to both saline and sodic soils, which are classified

under the major groups of Solonchaks and Solonetz respectively in the FAO-Unesco

(1988) soil classification system. These soils contain appreciable quantities of soluble

salts and/or salt-containing compounds in their profile that adversely affect the

growth of most crop plants.

Salt-affected soils are not uncommon in arid and semi-arid regions of the world

where annual precipitation is insufficient to meet potential evapotranspiration. The

salts may originate mainly from dissolution or weathering of rocks and soil minerals,

groundwater or human activities such as use of saline water for irrigation purposes.

Salty water from groundwater tables within a few meters of the surface can move

upwards by capillary action to the soil surface, where the water evaporates and leaves

behind the salts.

The arid and semi-arid climate of Eritrea, especially in the Red Sea coastal plains and

in the western lowlands, is a favourable environment for the development of saline

and sodic soils (Maskey, 1984). According to the FAO (1994) general soil

classification map of Eritrea (at a scale of 1:3,000,000) solonchak soils cover about

11,200 km2 of land, predominately found along the Red Sea coastal zones of the

country. However, the occurrence of solonetz soils is not reported on this map,

presumably because they are only found in small and localised areas, and also due to

the fact that this map has not been verified on the ground.


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High levels of salts in soils reduce plant growth and crop yield in a number of ways.

There may be direct toxic effects, especially from elements such as sodium, chlorine

or boron. Ionic imbalances may also be created in plants. Plants may also suffer from

physiological drought as water availability to plants is lowered due to the high

osmotic potential of salty water in the soil solution (FAO, 1988).

Sodic soils contain a high exchangeable sodium percentage (>15%) and also have a

high pH value (mostly in the range of 8.5 to 10). These soils seriously affect plant

growth in a number of ways. Sodium ions have an adverse effect on plant metabolism

and nutrition. Most plants cannot tolerate the high pH associated with sodic soils.

The high pH leads to low micronutrient availability and decreases the availability of

macronutrients such as calcium, magnesium and phosphorus. Accumulation of

elements such as sodium, molybdenum and boron in plants can result in direct

toxicity and may lead to plant injury or reduced growth and eventually death in more

sensitive plants. Anions associated with sodicity such as high HCO3− are directly

toxic to plants.

In sodic soils, plants suffer from oxygen deficiency as sodium disperses clays and

organic matter leading to structural breakdown of the soil particles and consequent

low porosity (FAO, 1988). Dispersed organic matter may accumulate at the surface

of poorly drained areas and impart a black colour; hence the common name ‘black

alkali soils’. Moreover, these properties reduce water infiltration and aeration in the

soils and hinder the growth of roots, which may eventually lead to loss of arable land

unless appropriate ameliorative measures are taken for the reclamation of the soils.

The Government of Eritrea is committed to enhancing food security in the country

and to developing sustainable agricultural production (via developing large-scale

irrigation schemes) in the coastal plains and in the western lowlands of the country.

However, most of the irrigated soils in these areas are predominantly affected by salts

presumably from the weathering of rocks and/or minerals containing salt compounds

and/or the use of saline or sodium–rich groundwater for irrigation. Therefore, there is

an urgent need to investigate and learn how to deal with the problem of salt-affected

soils before larger areas are put under irrigation. In other words, managing the SAS

requires a detail description of the nature and properties of the soils and water.

Saline soils may be controlled with careful irrigation management, but sodic soils

(with structural collapse) present a much more difficult management problem.


4

Because the reclamation of sodic soils involves not only leaching out the soluble salts

but also replacing exchangeable sodium with calcium and improving the physical

properties of the soils. It is, therefore, essential that signs of developing SAS,

particularly sodicity problems, be recognised at an early stage, so that preventative

control measures can be put in place and on time.

1.3. OBJECTIVES OF THE STUDY

The main objectives of this study are:

i) To determine the extent and degree of soil and water salinity and/or sodicity

in Shemshemia irrigation scheme;

ii) To recommend possible soil chemical, physical, and/or biological

amendments in order to improve or reclaim the salt-affected soils;

iii) To produce an appropriate preventative checklist for unaffected sodic areas so

as to prevent any future salt and/or sodium hazards in the Shemshemia

irrigation scheme and its vicinity.

1.4. TERMS OF REFERENCE

In brief, the ToR for the consultants and assistants are shown in Table 1.1. The

detailed ToR for each consultant are appended in this report. The ToR of the study

team is to fulfil (at least) the three main objectives of this study, which have been

mentioned above. These objectives are to be meet by carrying out field surveys and

measurements and by conducting laboratory analysis.

The study team consisted of four members with some additional help from field

assistants and labourers. The team members had slightly different responsibilities as

shown in the above table. The 4th team member i.e. Mr. Mussie Ykeallo was only

involved in the preliminary field survey and proposal writing.


5

Table 1.1. Terms of reference for the various consultants and assistants involved in the project.

Consultants & assistants Institution ToR

Dr. Mehreteab Tesfai † University of Asmara Overall organisation, preparation of

project proposal, field surveys, data

collection and analysis, report writing

Dr. Virginia Dawod ‡ University of Asmara Preparation of project proposal, data

analysis, report writing

Mr. Kiflemariam Abraha ‡ Ministry of Agriculture Field survey, data collection and

analysis and report writing.

Mr. Mussie Ykeallo ‡ University of Asmara Preliminary field survey and proposal

preparation.

Field assistants University of Asmara Field data collection and recording.

Daily labourers Shemshemia farm Preparing profile pits and auger holes.

† Team leader, ‡ Team members.

2. DESCRIPTION OF THE STUDY AREA

This chapter describes the physical and socio-economic settings of the Shemshemia

area in particular and the upper Gash sub-region in general.

The state of Eritrea is divided into six administrative regions (equivalent to

provinces). The Gash-Barka region is one of the six administrative regions, and

includes, among others, the upper Gash sub-region (equivalent to a district). The

upper Gash sub-region comprises 19 administrative units (locally called ‘kebabi

mimihidar’) which consist of about 104 villages.

2.1 LOCATION & TOPOGRAPHY

The study area, i.e. the Shemshemia farm, is located approximately 45 km along the

road southwest of Barentu, the capital of Gash-Barka region. More precisely, it is

found about 9 km west of Tokombia, (the administrative town of the upper Gash sub-

region) on a left junction from the road to Barentu (see Map 2.1).

Map 2.2 shows the topographic base map of the Shemshemia farm. The Shemshemia

farm is situated along the valley of the River Gash, which forms the western


6

boundary of the farm. The largest part of the study area consists of a flat to almost

flat plain covering the western and central section of the farm. To the eastern part of

the project farm there is a range of hills and undulating plains. The Shemshemia farm

lies at a latitude 14°47’N and longitude of 37°28’E, at an average elevation of 885 m

above sea level.

The Shemshemia farm covers an area of about 125 hectares. A substantial part of the

area is devoted to the cultivation of citrus plants and cereals (mainly sorghum and

maize). A small area of land is occupied by houses for residences of farm workers

and workshops used for training and maintenance of farm implements. These

buildings, however, were demolished in May 2000 during the Ethiopian invasion into

the western lowlands of Eritrea.

2.2 POPULATION

The population of the upper Gash is estimated to be 50,000 people in about 12,800

households. The population density is about 10 persons per km2, which is low

compared to other regions of Eritrea. Various ethnics groups live in the area, namely

‘Kunama’, (the dominant ethnic group) followed by ‘Tigrigna’ and ‘Tigre’. The main

local languages spoken in the region are ‘Kunama’, ‘Tigrigna’ and ‘Tigre’.

Like other parts of Eritrea, most of the population (>80%) living in the rural areas

around Shemshemia is engaged in traditional agriculture, mainly growing crops and

raising cattle. The proportion of cultivated land to farming population ranges from

2.2 to 2.7 person ha-1 (MoA, 2000). At present, the Shemshemia farm has about 15

permanent workers. The average farm household size is about 5 persons. A large

number of daily labourers are employed during the peak season, particularly during

harvesting of the fruit and grains.


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Map 2.1. Location of the Shemshemia area in the upper Gash sub-region, Eritrea.


8

Map 2.2. Topographic base map of Shemshemia study area.


9

2.3. CLIMATE

Eritrea is divided into six agro-ecological zones on the basis of topography, climate

and soil conditions (FAO, 1997). These are moist lowland, arid lowland, semi-desert,

moist highland, arid highland and sub-humid zones.

Table 2.1. Climate (long-term) data at Barentu meteorological station.

Month Air temperature, °C Relative

humidity, %

Rainfall

mm

PET

mm

Maximum Minimum Mean

January 32.5 14.8 23.7 45 0 126

February 31.1 14.6 22.9 40 0 133

March 35.1 16.1 25.6 37 1 173

April 37.3 18.8 28.1 36 10 191

May 37.5 19.1 28.3 36 22 207

June 34.0 17.0 25.5 41 74 183

July 30.3 17.8 24.1 65 142 144

August 29.1 17.0 23.1 69 178 134

September 32.0 17.1 24.6 55 78 149

October 34.3 18.0 26.2 47 8 176

November 34.0 17.0 25.5 49 3 130

December 32.3 15.7 24.0 48 0 116

Mean 33.3 16.9 25.1 47.3 - -

Total - - - - 506 1,862

PET: Potential evapotranspiration.

Source: Civil Aviation Authority of Asmara, Eritrea.

Table 2.1 shows long-term climate data collected at Barentu meteorological station,

which is the nearest station to the Shemshemia farm (45 km away). The mean air

temperature varies from 22.9°C in February to 28.3°C in May. The relative humidity

is above 50% in the rainy months of July to September. More than 90% of the rain

falls in the four months of June to September (Table 2.1). The potential

evapotranspiration exceeds the rainfall in most months except in August, which is the

wettest month of the year. The period from December to February can be considered

as the dry season.

Based on the above climate information and topographic conditions of the study area, the Shemshemia area falls within the moist lowland agro-climatic zone of Eritrea.


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2.4. GEOLOGY

In general, the geology of the Gash catchment is characterised by Pre-Cambrian

rocks, composed of amphibole schist, chlorite schist, cordiorite schist and other

schists with porphyritic, lateritic or phylitic structure. Chlorite schist are intercalated

by diorites and diabases (MoME, 1999).

Very little information is available on the specific geology of the Shemshemia area.

According to the report of the MoME (1999), large areas around Shemshemia farm

are formed of meta-sedimentary rocks, which consist of both clastic and chemically

precipitated sediments. The clastic sediments are characterised by faint lamination

and bedding. These sediments consist of phyllites, slates, siltstone, sandstone,

mudstone and patches of quartzite, which are all metamorphosed.

2.5. HYDROLOGY & DRAINAGE

Eritrea has five main river drainage systems. These are Mereb–Gash, Setit, Barka-

Anseba, the Red Sea river basins, and the enclosed Danakil basin (see Table 2.2).

The Mereb-Gash and Setit river basins (mainly found in the Gash-Barka region) drain

into the Nile basin.

The Gash River flows along the western boundary of the Shemshemia farm. Its upper

catchment stretches from the southern part of the central highlands of Eritrea to the

southwestern part of the country and its lower catchment extends to the Sudanese

border. The river flow originates mostly in the upper highlands of Eritrea. The Gash

River is ephemeral but carries a significant quantity of sediment. The river deposits

large amounts of suspended sediments in the southern and western plains of Eritrea

(e.g. in the Aligheder irrigation schemes), and in the Kassala plains in eastern Sudan.

The river discharge is less than 0.5 m3 s-1 during the low flow season, i.e. from

October to May, while during the rainy months, especially in July and August, the

river water level reaches up to 10 m. It fluctuates appreciably, even within a span of

24 hours. During peak flows, the river may discharge about 500 3 s-1. In the past

decade or so, the river has flooded the low-lying areas of the Shemshemia farm

(Andemariam, pers. comm, 2001).


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Table 2.2. Mean annual flow volume of the major drainage basins, their catchment area and rainfall.

Drainage

basin

Catchment

area

Catchment Annual flow

Vol.

Mean annual

runoff coeff.

(km2) Annual rainfall

(mm)

Rainfall vol.

(Mm3)

(Mm3) -

Red Sea 44,689 300-400 13,406.7 444 0.152

Barka-Anseba 39,506 350-400 13,827.1 41 0.045

Mereb-Gash 23,455 500-700 11,727.5 532 0.003

Denkil basin 10,532 200 2,106.4 135 0.033

Setit basin 7,517 600-700 4,888.1 49 0.010

Total 125,699 - - - -

Source: WRD (2000).

The groundwater level along the Gash riverbank varies from 3 to 4 m during the

rainy seasons and deeper (about 8 m) in the dry season. The Shemshemia irrigation

scheme gets its supply of water from a well, which is found close to the riverbank of

Gash. Water is drawn by centrifuge motor pumps which have a diameter of 150-200

mm and a horse power of 60-80.

Gully erosion is seriously threatening the non-irrigated land in the northern part of

the farm. The cause of erosion is perhaps the excessive runoff from the nearby hills

and low vegetal cover of the upland areas. Soil and water conservation measures are

urgently needed in order to arrest the soil erosion and to promote better soil moisture

conditions so that these lands could be utilised for cropping and/or pasture.

2.6. NATURAL VEGETATION & LAND USE

The upper Gash area is covered with different species of woodland trees, shrubs and

herbaceous plants. Some of the dominant trees and shrubs found in the region are

species of Acacia, Balanites, Boswellia, Tamarix and Zyziphuse and riverine trees

such as doum palm (Hyphayene thebaica). The leaves of Dum plants are used for

making sacks, baskets, mats and other crafts.

In the past decades, the doum plants covered a large part of the area along the Gash

riverbank. However, the expansion of irrigation schemes along the riverbanks has

negatively affected the riverine forests, since a large number of trees (e.g. doum

plants) have been deforested from the area. As a result, riverbank erosion is more

severe particularly during the rainy season. Protection of the remaining doum plants


12

and growing grass species along the riverbank may help mitigate the problem of bank

erosion along the Gash River.

The main land use in the Shemshemia farm is irrigated agriculture, dominantly for

citrus crops and some vegetables. A small area of the valley land is used for growing

sorghum and maize using the seasonal rainfall. There are riverine tree species

(notably doum plants) growing along the bank of the Gash River. Uncultivated lands

covered with sparse grass vegetation are found in the sodic areas, in the marginal

lands near the foothills and in the plains along the river valley.

3. METHODS OF STUDY This chapter explains the methodology used in this study i.e. field survey and

measurements, sampling and laboratory analysis, the soil classification and mapping

methods adopted, the contents of questionnaires, and the group discussions held with

the farmers working in the Shemshemia farm.

3.1. FIELD SURVEY & MEASUREMENTS

The study team made a preliminary visit to the Shemshemia area on 25th to 27th May

2001 to make initial observations and become familiarised with the area. A project

proposal and timetable of activities was then drawn up. The main field survey took

place from 13th to 19th September 2001. The field survey was delayed from the

original plan of July, due to the exceptionally heavy rains in the study area from June

to August.

Prior to conducting the main fieldwork, all available information regarding the

environment of the Shemshemia area and materials such as previous study reports,

topographic maps covering the area were collected, compiled and studied. A

topographic map of the Shemshemia farm (on a scale of 1:2,000 with 1 meter contour

intervals) was acquired from NCEW (1997). This map was used a base map for the

fieldwork.

Firstly, the boundary of the Shemshemia farm was verified in the field by tracing


13

the benchmark (BM) points (which were already installed in the field) as well as by

plotting the BM points onto the topographic base map. This ground verification was

carried out by locating the BM points on the Universal Transverse Mercator (UTM)

grid using the Global Positioning System (GPS-315) (see Table 3.1). Major land

units comprising irrigated and currently not irrigated land units were then identified

during the field survey.

Profile pits and auger holes were selected on each land unit and their positions were

also located on a UTM grid using the GPS. Afterwards, the locations of the pits and

auger holes were transferred to the base map.

Because of the uniform flat terrain and great homogeneity of the soils, the

observations were made at an overall density of about 1 per 5 ha of land. In total, 5

profile pits and 10 auger holes were dug and prepared for soil descriptions and

analysis. The dimensions of the soil pits were about 1.5 meter deep and 1.5 meter

long unless otherwise prevented by the presence of rock, large stones or very coarse

gravel. Exposed sites such as river cuts were also used to study the morphology of the

riverine soils.

Table 3.1. Soil profile and auger hole location sites in Shemshemia farm.

Profile/auger no. UTM-eastings UTM-northings Elevation, m a.s.l.

P1 331899 1638490 900

P2 331031 1638266 920

P3 331000 1637940 885

P4 331348 1637592 905

P5 330900 1638300 915

A1 331649 1636854 885

A2 330993 1637961 890

A3 331067 1637883 887

A4 331375 1637767 885

A5 331188 1637727 887

A6 331116 1637705 882

A7 331014 1637674 888

A8 330997 1637703 885

A9 330998 1637704 885

A10 330998 1637704 885

SP: Profile pits, A: Auger holes.

The soils were described according to the international standards laid down by FAO:

Guidelines for soil profile descriptions (FAO, 1990). General information on the


14

characteristics of the profile sites as well as information related to the identification

and soil horizon descriptions was recorded on standard soil description forms

conforming to the FAO-ISRIC (1998) soil coding sheet. Most of the field data such

as slope and elevation were measured, and others such as land use, vegetation and

erosion were observed and recorded on the data sheet.

Some soil properties were determined in the field, e.g. soil texture by feel method

and soil colour by comparison with Munsell soil colour charts (Munsell, 1994), and

calcium carbonate contents of the soils by adding 10% dilute HCl to the soil material.

A drainage problem could lead to sodicity problems and should be assessed if an

effective sodicity reclamation method is to be suggested. In this respect, the

infiltration rates of the soils in the non-irrigated fields (in the sodic land) were

measured using a double ring infiltrometer and saturated hydraulic conductivity of

the soils was tested following the inverse auger hole method (Landon, 1991).

3.2. SOIL AND WATER SAMPLING

A total of 37 soil samples were collected from 5 profiles and 10 auger holes for

laboratory analysis. These constituted 15 samples from the pedogenetic horizons in

the soil profiles and 22 samples from topsoil and subsoil depth by augering. The

samples were sent to the soil science research laboratory of the MoA for further soil

physical and chemical analysis to complement the field observations and analysis.

In order to ascertain the possible causes of sodicity problems in the fields from the

water aspect, water samples were taken from the river Gash (at three replication

sites), from the open hand dug well and from the irrigation canals in the fields. A

total of five water samples were taken from these sites using a manual bottle

sampling method. The bottle samples had a capacity of 500 ml.

3.3 LABORATORY ANALYSIS OF SOILS & WATER

Before the soil analysis in the laboratory, the soil samples were air-dried, crushed in a

porcelain mortar and passed through a 2 mm sieve. The method of analysis used for


15

each of the determined soil properties is described in Table 3.2.

The water samples were brought to the water analysis laboratory of the Water

Resources Department at the Ministry of Land, Water and Environment. The water

samples were analysed for EC, pH, soluble cations and soluble anions following the

standard procedures by HACH (1986). Table 3.2. Soil physical and chemical analysis methods used in this study. †

Soil property Method of analysis

Particle size analysis (ϕ) Bouyoucos hydrometer

Soil texture (class) USDA textural triangle

Bulk density (g cm-3) Core method

Infiltration rate (cm hr-1) Double ring infiltrometer

Saturated hydraulic conductivity (m day-1) Inverse auger hole method

Soil reaction, pH (H2O) pH meter, soil: water (1:2.5)

Electrical conductivity (d S m-1) EC meter, soil: water (1:2.5)

Organic carbon (%) Walkey-Black method

Total Nitrogen (%) Macro Kjeldhal digestion

Available P (mg kg-1) Olsen’s method

Available K+ (mg kg-1) Flame emission Photometer

Exchangeable Na+ (meq 100g-1) Flame emission Photometer

Exchangeable cations of Ca 2+ and Mg 2+ (meq 100g-1) EDTA Titration of 1M ammonium

Cation exchange capacity (meq 100g-1) 1M ammonium acetate extract

CaCO3 (%) Rapid titration method

HCO3- (mg l-1) Titration with 0.005M sulphuric acid

SO42 - (mg l-1) Extract with barium chloride

Cl- (mg l-1) Silver nitrate method

CO32- (mg l-1) Titration method

† (Klute, 1986; John, et al., 1996).

3.4. SOIL CLASSIFICATION & MAPPING METHODS

The soils of the Shemshemia farm were classified on the basis of their

morphological, physical and chemical properties. Some of these properties were

measured and/or observed in the field, while others depend on the results of

laboratory analysis.

The boundaries of the land units (identified in this study) and contour lines were

digitised using a digitizer. Distances between the BM points were taken from the


16

survey map while angles between the points were measured by a protractor. These

data were entered into the database of the Geographic Information System (GIS)

ARC/INFO program. Then, all attributes data were processed and analysed by

ARC/View GIS version 3.2. Finally a digital topographic base map of Shemshemia

farm (Map 2.2.), land use types (Map 4.1.) and soil use map (Maps 4.2.) were

produced on a scale of 1:2,000.

3.5. INTERVIEWS AND GROUP DISCUSSIONS

A checklist questionnaire was prepared in line with the objectives of this study. The

contents of the questionnaire include data on socio-economic conditions, crops

grown and yield, land use types, soil conditions, water management, agricultural

problems and their possible solutions and development potentials of the Shemshemia

area (see Annex C).

Groups of people comprising old and young were interviewed to gather information

on the history of the farm, especially its development and production problems

encountered since the establishment of the farm. Group discussions were also carried

out with 15 farm workers to identify the key problems facing the Shemshemia farm

and their possible solutions.

4. FINDINGS & DISCUSSION

This chapter details the data collected during the field surveys, observation and

interviews made in the study area and also discusses the results of the soil and water

analysis conducted in the laboratory.

4.1. THE FARMING SYSTEMS ANALYSIS

The following sections of this chapter describes the farming system of the

Shemshemia area; the historical development of the farm, cropping systems and

water quality analysis. Furthermore, the report identifies production problems of the

Shemshemia farm and their possible solutions from the farmers’ perspectives.


17

4.1.1 Historic review of Shemshemia farm

In the early 1940s, an Italian national, Armando Motanti, carried out a reconnaissance

geological survey for mineral exploration in the Shemshemia area. He used to mine

precious minerals like gold in the Shemshemia area and its vicinity, and used to sell

several quantities of gold to Asmara and other towns in Eritrea. Later, the gold

mining was not encouraging, presumably due to low resources of gold in the area. He

then planned to establish irrigation schemes in the Shemshemia area.

In 1947, Mr. Motanti cleared the land and ploughed the lower fields along the course

of the Gash River in the Shemshemia area. He dug water well near the bank of the

river to irrigate the fields. He then planted banana seedlings but the seedlings did not

grow well due to high salt contents in the soils (Andegiorgis Embaye, pers. comm.,

2001). The banana plants (Musa sp.) are generally recommended to grow on soils

with no salt problems (i.e. ECe < 1 d S m-1) (Landon, 1991).

Later on, other Italian concessionaires used to grow vegetable crops such as tomato,

onion, and pepper in Shemshemia area using a canal irrigation system. The vegetable

production from the area and its surroundings was quite high and made a significant

contribution to the domestic market supply. During good years, large quantities of

fresh vegetables were even exported to neighbouring countries like Sudan and other

regions to the Gulf States and Europe. In addition, field crops such has cotton and

groundnuts were also grown using the seasonal rainfall.

In 1974, with the outbreak of the socialist revolution in Ethiopia, many of the Italian

concessionaires who were engaged in agriculture and other activities left to their

home country and some to other parts of the world. During this period, the armed

struggle for Eritrean independence was highly intensified. In the late 1970s, a large

part of the Eritrean territory was emancipated from the military regime of Ethiopia by

the Eritrean Peoples’ Liberation Front (EPLF), the ruling party now in the country.

The Shemshemia farm was virtually at a standstill from 1974 to 1991. In 1991, when

Eritrea got its independence after 3 decades of war for liberation, the GoE gave a

high priority to developing the agricultural sector under its Recovery and

Rehabilitation Programmes. The government invited all private sectors and other

development agencies to rehabilitate the agricultural infrastructure, which had been

demolished in the various parts of the country. Interest was shown in the irrigation


18

schemes in the upper Gash valley, among which was the Shemshemia irrigation

scheme.

In 1992, an Eritrean investor, Afeworki Berhane, embarked on developing the

Shemshemia irrigation farm. He renewed the motor-pumped well and constructed a

feeder road that links (the Shemshemia farm) to the road network of Barentu to

Tokombia. He also developed several farm roads within the farmlands. He planted a

large number of orange trees and some lemon trees in the irrigated fields. He also

used to cultivate sorghum and maize crops during the rainy season.

In 1995, the Shemshemia irrigation farm was transferred from private ownership to

the National Confederation of Eritrean Workers (NCEW). The NCEW has repaid to

Mr. Afeworki Berhane all costs he incurred to develop the Shemshemia farm. The

staff of NCEW supervises and manages the farm. At present, there are about 15

permanent workers who are engaged in the farm. Apart from this, a large number of

daily labourers are also employed during the peak cropping seasons (such as

ploughing, harvesting of fruits and vegetables and also during harvesting of grains).

4.1.2. Crop production systems

The farming system in Shemshemia is characterised mainly by commercial irrigated

agriculture. However, most of the farmers in the surrounding area are engaged in

small-scale subsistence farming in a crop/livestock mixed production system using

simple traditional farming implements.

In Eritrea, land is under the domain of the state. Since 1991, the GoE has been

actively encouraging the development of commercial irrigated agriculture through

adopting the concession system. Since then, many concessionaires have been offered

land (for e.g. in the southwestern lowlands of Eritrea) on a long lease-based system at

nominal cost. Most of these concessionaires have developed small-scale irrigation

schemes along the course of Gash River basin, where they grow high value

vegetables and fruit crops.

The upper Gash valley is considered as one of the best arable agricultural lands in the

southwestern lowlands of Eritrea. In the upper Gash, particularly in the Shemshemia

farm, citrus fruits such as oranges and lemons are largely grown and vegetable crops

such as tomato and pepper in a smaller area. All these crops are grown using

irrigation. Field crops such as sorghum, maize and bulrush millet (Pennisetum


19

typhoides) as the cereals and oilseed crops (such as sesame and groundnuts) are also

grown using the rainfall in the months of July to September.

In Shemshemia farm, there are about 5,500 orange trees, which were planted in 1996.

The spacing between the rows and within the rows is 6 m by 6 m. The lemon fields

constitute about 400 trees and their spacing is the same as for the orange trees. The

lemon trees were planted in 1998. During the same year, about 130 grape fruits were

also planted in the irrigated fields. Mineral fertilisers (such as DAP and Urea) and

organic fertilisers are seldomly applied in the citrus fields.

Table 4.1 presents the land use types and land coverage in the Shemshemia area. At

present, about 10% of the total area in Shemshemia is under irrigated land but a large

part of the area (about 56%) is not yet cultivated mainly due to the constraints

mentioned in the following subsections. Table 4.1. Land use and land coverage by ha and % in Shemshemia area.

Land use Coverage

ha %

Sodic land 5.3 3.3

Rainfed land 13.2 8.2

Irrigated land 15.9 9.9

Riverine forest land 35.6 22.1

Uncultivated land 90.8 56.5

Total 160.8 100.0


20

Map 4.1. Land use types of Shemshemia area.


21

4.1.3. Irrigation water quality

Table 4.2 shows the water sample site locations in the Shemshemia farm. These

samples were taken during the rainy season and after the season was over. Water

samples were collected at predetermined depths in the well, in the Gash riverbed and

from the canals in the fields.

Table 4.2. Water sample sites locations in Shemshemia irrigation scheme. Sample sites UTM co-ordinates Altitude

(m) a.s.l.

Eastings Northings

W1 330856 1637742 930

C1 331075 1638276 920

R1 330900 1638300 915

R2 330735 1637470 910

R3 331200 1637090 910

W1: well water

C1: canal water

R1: river water (replication 1)



The main criteria used for judging the quality of irrigation water are its chemical

characteristics such as the total salt concentration (as measured by electrical

conductivity) and relative proportions of cations as expressed by sodium adsorption

ratio (SAR) and other water characteristics such as bicarbonate and boron contents.

Table 4.3 shows the water temperature, pH and salinity values of the water analysis

carried out in the laboratory. The pH values ranged between 7.1 to 7.8 which falls in

the normal pH range (i.e. 6.5 to 8.4) for irrigation water. The Gash river water (the

primary source of irrigation water for the Shemshemia farm) has an EC below 300 µ

S cm-1, 200 mg l-1 of TDS and a SAR of 4, which are rated as low saline and low

sodium water. The river water therefore has no degree of restriction on use for

irrigation.

All the water samples measured in the range of 270 to 472 µ S cm-1, which are low to

moderate salt contents according to classification of irrigation water salinity by

Landon (1991). These waters can be used to irrigate low to moderate salt tolerant

crops such as citrus and vegetables.


22

Table 4.3. Water temperatures and water salinity values in Shemshemia area.

Sample

site

Temp 0C

PH

-

EC

µ S cm-1

TDS

mgl-1

W1 20.2 7.8 472 267.7

C1 19.6 7.3 273 148.8

R1 20.3 7.1 270 158.5

R2 20.2 7.2 272 158.7

R3 20.3 7.8 286 162.4

Mean 20.1 7.4 314.6 179.2

Tables 4.4 and 4.5 present the water chemical characteristics of soluble cations and

anions, respectively. In general, all the water samples showed low concentrations of

soluble cations of Ca2+, Mg2+, Na+, K+ and low contents of soluble anions of HCO3-,

SO42-, Cl-, NO3

-N, F-, B and Mn. The SAR in the water samples was below 10, which

denotes low sodium water according to the classification of irrigation water sodicity

by Landon (1991).

Table 4.4. Water analysis of soluble cations and derived values of SAR in Shemshemia area.

Sample site Ca2+ Mg2+ Na+ K+ SAR

mg l-1

W1 51.2 25.9 20.2 3.7 3.2

C1 23.2 7.3 18.1 9.6 4.6

R1 27.2 7.6 17.4 1.5 4.1

R2 29.1 6.4 16.6 1.9 3.9

R3 28.8 5.5 16.7 2.2 4.0

Mean 31.9 10.5 17.8 3.8 4.0

Table 4.5. Water analysis of soluble anions in Shemshemia area.

Sample HCO3- SO4

2- Cl- NO3-N F- B Mn

mg l-1

W1 287.9 20 1.6 0.88 0.27 0.3 0.2

C1 141.5 12 4.0 3.1 0.31 0.3 0.4

R1 129.3 28 2.0 8.4 0.38 0.1 1.1

R2 131.4 27 1.2 9.1 0.37 0.2 1.2

R3 136.6 27 0.4 11.9 0.39 0.2 1.0

Mean 165.3 22.8 1.8 6.7 0.34 0.22 0.78

All the water samples have been found to be of good chemical quality for irrigation

and other uses. For example, the well water measured 0.3 mg B l-1, which is well

below 1 mg B of per litre (i.e. maximum concentration of trace elements in


23

irrigation water) as suggested by FAO (1985 and 1988). Normally, citrus fruits are

sensitive at B contents of 0.5-0.75 mg l-1. All the water samples measured below 4

meq Cl l-1 and this indicates no chloride toxicity.

4.1.4. Production constraints

The main agricultural production constraints in the Shemshemia irrigation scheme

and their possible solutions are presented in Table 4.6. These problems were

identified during the interviews and groups discussion made with the farmers in the

area. Table 4.6. Production constraints and possible solutions in Shemshemia farm.

Constraints Possible solutions

Shortage of labourers �� Use of mechanised farming practices

Shortage of irrigation water pipe-lines �� Construct water reservoirs in the central part of the

farm to irrigate the upper and middle parts of the fields

Salty land �� Apply physical treatments like deep ploughing

River bank erosion �� Protection of riverine trees and growing grass sp.

along the riverbanks

Lack of motorised sprayers �� Provide motorised sprayers for pest control

Shortage of farm implements �� Provide hand farm tools

Poor farm management �� Employ qualified farm manager and develop

monitoring and evaluation systems

The suitability of irrigation water for agricultural development, however, is not only

evaluated by the quality of the irrigation water but also by the soil quality (like nature

and extent of salts in the soil profile and drainage conditions of the soils) and plant

characteristics.

One of the main production problems in the Shemshemia farm was the salty land

(Table 4.6). In order to manage these lands, a detail description of the soils of the

Shemshemia area is presented hitherto, followed by possible reclamation and

management practices for the sodic areas and prevention methods for non-sodic areas

in the Shemshemia area and its vicinity.


24

Map 4.2. Soil types of Shemshemia area


25

4.2. The Soils of Shemshemia Area This section describes the range of characteristics of the soil units identified in the

study area and their classification category.

The soils of the Shemshemia farm were studied in September 2001, with the aim of

assessing their main characteristics and their variability over the study area.

Based on field observations, the soils of the Shemshemia farm are broadly classified

into two main soil-mapping units (see Map 4.2). These are soils developed on

irrigated lands and those on currently non-irrigated lands (see profile descriptions in

Annex A).

The surveyed area covered irrigated and non-irrigated sites within the farm. The

irrigated sites were planted with citrus trees. The non-irrigated sites could be divided

into two: land that is cultivated during the rainy season and land that is currently

uncultivated due to its salt problem (which was in fact identified as a sodicity

problem). One uncultivated site on the riverbank was also sampled. The non-irrigated

areas were being used as grazing or fallow land at the time of sampling. The grazing

area in the northern part of the site was severely grazed, while that from the centre of

the site southwards to the River Gash was covered with long grass. There were some

bare patches without grass where a dark brown crust was seen on the surface of the

soil. It had not rained for almost two weeks prior to carrying out the field visit, yet on

the grazing areas and to some extent on the citrus plantation, water still remained on

the surface in these bare areas, it had not drained or infiltrated into the soil. The soils

in these areas also showed poor workability and were difficult to dig.

4.2.1. Soil physical properties of the Shemshemia area

a) Irrigated soils: The irrigated soils are all soils being used for cultivating fruit and

vegetable crops. These soils are mainly used for growing citrus fruits like orange,

lemon and grapes. The irrigated soils are found in the citrus fields located in the

middle part of the Shemshemia project farm. Water is pumped from the well that is

located near the river Gash and transported by water pipes to irrigate the fields. In the

fields, each citrus plant receives water by watering the soil around it, a kind of basin-

furrow irrigation system. The irrigated soils cover around 16 ha (which is 10% of the

total land area) in Shemshemia.


26

The irrigated soils are developed on the almost flat plains of the Gash river valley.

They are presumed to be formed from the weathered parent rock (in situ). The soil

profiles show a well-developed Ap horizon (the plough layer) in the citrus fields. In

addition, a thick subsoil B horizon is found (which have > 1 m thickness), and in the

lower part of the profile, a transitional BC horizon is developed.

In general, the irrigated soils are deep (on average > 1.5 m), dark brown in colour,

structureless at the surface but with weak sub angular to angular blocky structures

developed in the subsurface soils.

Soil texture and colour: Texture is a basic property of soils because it affects both

the physical and chemical properties such as infiltration rate, porosity, fertility, etc,

(FAO, 1979). Table 4.7. Particle size distribution and colour of topsoils (0-0.20 m) in irrigated soil units.

Profile/ Sand Silt Clay Soil texture Soil colour

Auger no. % % % class moist dry

P4 61 24 15 sandy loam 7.5YR 3/3 nd

A1 25 42 33 clay loam nd nd

A2 28 45 27 loam nd nd


A4 65 21 14 sandy loam nd nd




Mean 40 34 26 loam - -

nd: not determined.

The particle size distribution and colour of the soils in the top 0.20 m are presented in

Table 4.7. Except for profile pit P4 and auger A4, the soils have more than 25% clay

content. The sand content in P4 and A4 were above 60%, probably because of the

local topography where coarse fragments are eroded from nearby hills and deposited

on these fields. Nonetheless, the soil units are fairly uniform in texture. Most of the

soils are loams with on average 40% sand, 34% silt and 26% clay (Table 4.7).

The colour of the soil profile P4 was dark brown at moist conditions, but the colour

of the soils at dry conditions was not determined since the soils were moist at the

time of survey.


27

Soil structure: In the top 20 cm of the profile pit P4, which coincides with the

surface horizon and the plough layer (Ap), the soil particles do not have well-

developed aggregates. This may be due to the effect of tillage and cultivation on the

soils. The soils showed firm consistence under dry conditions and are slightly sticky

under wet conditions.

Further down in the profile (in the subsoil layer), the soils have developed weak

subangular blocky structures, with many termite channels in the soil peds.

Bulk density and porosity: The dry bulk density (BD) of the unit-A soils was

measured by taking undisturbed soil samples using a core sampler in a standard

volume sample ring (135.5 cm3). The samples were taken from each pedogenetic

horizon including the topsoil and subsoil layers.

Table 4.8. Bulk density and porosity of soils at different depth in the irrigated soil unit.

Sample depth

cm

Bulk density

g cm-3

Porosity

%

Risk of compaction

0-20 1.31 50.6 No

20-96 1.37 48.3 No

96-128 1.22 53.9 No

128-164 1.22 53.9 No

Mean 1.28 51.7 -

The bulk density and porosity values of the irrigated soils showed no risk of

compaction in the topsoil as well as in the subsoil depths (Table 4.8)

Drainage and soil moisture: The irrigated soils showed no signs of mottling in their

profile. Thus, the soil profile can be categorised as well drained (drainage class 4).

Moreover, the loamy textural characteristics of this soil unit (see Table 4.7.)

substantiate the drainage class to be well drained.

The external drainage conditions of the irrigated sites show slow run-off on the upper

part of the fields. However, a large part of the site neither receives nor sheds water.

But a small plot of land just above the sodic land was highly saturated with water. In

this plot, the infiltration rate is very slow where water stays on the surface for more

than a few days after irrigation. This may be largely due to the hard compacted

horizon found in the subsoil layer. In this plot, the citrus plants have stunted growth

and have not produced fruits since planting in 1996.


28

The groundwater level in the irrigated fields varies during the dry and rainy seasons.

At the time of survey (i.e. at the end of rainy season), the depth of the ground water

table in the water well was about 8 m, which is classified as a deep water table. The

moisture conditions of the soils at the time of description were moist throughout the

profile depth.

b) Currently, non-irrigated soils These soils constitute all land currently not irrigated. Part of this area is cultivated for

growing cereals during the rainy season, and part is the marginal areas (including the

barren sodic area), which are covered with sparsely grass vegetation and/or riverine

trees.

The rainfed lands are found in the northern section of the Shemshemia farmland and

the sodic lands along the lower portion of the farm parallel to the bank of the Gash

River. The area under sodic soils forms a strip of land across the farm. In total, the

non-irrigated soils cover about 135 ha (or 56%) of the study area.

The non-irrigated soils are presumed to have developed in situ from parent material

weathering. The soils have developed on nearly flat non-irrigated lands under natural

conditions.

Soil texture and colour: The particle size distribution of the soils is given in Table

4.9. Except for profile pit P1, all the studied profiles and augers showed loamy

texture in the topsoil layer.

Table 4.9. Particle size distribution and colour of topsoils (0-0.20 m) in the non-irrigated units.

Profile/ Sand Silt Clay Soil texture Soil colour

Auger no. % % % class moist dry

P1 58 29 13 Sandy loam nd 7.5 YR 5/8

P2 42 40 18 Loam 7.5 YR 3/2 7.5 YR 4/2

P3 22 49 29 Clay loam 7.5 YR 2.5/2 7.5 YR 3/2

P5 42 46 12 Loam nd nd

A7 35 38 27 Loam nd nd



A10 35 47 18 Loam nd nd

Mean 37 43 20 Loam - -

The range of particle size distribution (by percentage) is higher for silt, followed


29

by sand and clay particles. The colour of the topsoil profiles under dry conditions was

brown, and under moist conditions dark brown. The colour of the soils under moist

conditions was not determined in Profile P1 because the soils were dry throughout

their profile.

Soil structure and consistence: The soil structure in the ploughed layer (in the

rainfed land) was not well developed largely due to the effect of ploughing and

cultivation of crops. Weakly developed blocky structures are found in the surface

soils in the virgin land covered with grass. Subangular blocky structures have

developed underlying the plough layer in the rainfed land unit. In the virgin land unit,

angular blocky and weakly developed prismatic structures were found in the subsoil

layer (i.e. B horizon). This horizon was more than 1 m in thickness.

The profile pits P2 and P3 were very difficult to dig in the underlying topsoil layer,

which contained a compacted subsoil. A weakly developed natric B-horizon with

prismatic structures was noticed in profiles P2 and P3 at the time of carrying out the

soil descriptions. The soils are very deep (>150 cm) and the thickness of the horizons

in the studied profiles did not vary greatly.

In the topsoil layer, the consistency of the rainfed land unit under dry conditions is

loose and slightly sticky under wet conditions. This may be attributed to the high

content of sand (58%). The consistency of the sodic land unit is hard and sticky under

dry and wet conditions of the soils, respectively.

Bulk density and porosity: The dry bulk density of the non-irrigated soils in each

pedogenetic horizon of the studied profiles is shown in Table 4.10. The bulk density

of the soils increased with depth in both profiles. The increase of BD with depth

might be associated with the higher content of sodium in the subsoil than in of the

topsoils (Annex B). The mean value of the BD of the topsoils was 1.11 g cm-3 which

is common for uncultivated soils.


30

Photo 1. Dispersed organic matter in the surface soils of sodic land in Shemshemia farm.

Photo 2. Soil profile showing a hard compacted subsoil layer in sodic land units in

Shemshemia farm.


31

Table 4.10. Bulk density of non-irrigated soil unit in the topsoil and subsoil depth.

Depth P2 P3

g cm-3

Mean

Topsoil 1.18 1.05 1.11

Subsoil 1.37 1.25 1.31

Mean 1.28 1.15 1.22

Assuming an average value for particle density of 2.65 g cm-3, the total porosity of

most of the topsoils and subsoils were 58% and 51%, respectively. The risk of

compaction is more likely to occur in the subsoil than in the topsoil layer.

Drainage and soil moisture: The soils developed in the rainfed land unit are

classified as well-drained to excessively drained (drainage class 4 to 5) due to the

large proportion of coarse particles and less fine particles (i.e. clay) and no mottling

was observed in the profiles.

The topsoils in the sodic land unit do not show mottling but in the deeper subsoils

showed mottling conditions. The profile drainage class of this soil unit can be

categorised as poorly drained soils. This is due to the structural degradation

presumably caused by the high exchangeable sodium in the soils.

At the time of soil description, the moisture condition of the soils in the rainfed land

unit was dry throughout the profile, while the moisture condition of the soils in the

sodic land unit was moist throughout the profile. The moisture difference between

the soil units might be attributed to the higher water retention capacity due to the

higher clay content in the sodic land units.

The external drainage condition of the sodic units can be characterised as receiving

water because of their flat topography, while, the rainfed unit in the upper part of the

farm has a shedding water character.

Infiltration and hydraulic conductivity: The infiltration rate of the soils was

measured in the sodic land units where it is assumed that problems of drainage might

occur. The infiltration rate of the soils was measured using a double ring

infiltrometer. Figure 4.1 depicts the relationships of infiltration capacity of the sodic


32

soils versus cumulative time. The infiltration rate of the soils decreases rapidly at the

beginning and then reaches a constant rate (i.e. the basic infiltration rate was 1.6 cm

hr-1). This rate is moderately slow for surface irrigation system according to the

classification suggested by Landon (1991).

The slow infiltration rate of water into the soils might be associated with the high

ESP. The ill effects of excess sodium on the soil exchange complex imparts

structural instability to the soils giving poor soil physical properties. Moreover, the

infiltration rate of the soils becomes low and the soils have restricted internal

drainage. For this reason, the surface soil layers remain nearly saturated for few days

following irrigation or rain resulting in temporary anaerobic conditions. Soil

properties such soil texture and structure also influence the water intake rate.

Figure 4.1 .The infiltration rate of the sodic land unit in Shemshemia farm.

The saturated hydraulic conductivity of the non–irirgated soils was tested in the sodic

land unit following the inverse auger hole method also known as the Porchet method.

The method consists of boring a hole to a given depth, filling it with water and

measuring the rate of fall of the water level (Landon, 1991). This method was used

because the ground water table in Shemshemia area is very deep (often >8 m) both in

the dry and wet seasons. The hydraulic conductivity was the calculated as follows:

1.15 × r log [h(ti) + r/2] − log [h(tn) + r/2] [1]

where, k is saturated hydraulic conductivity (m d-1), r is radius of the auger hole

tn − ti

× 864 k =

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60 70 80 90 100 110 120Cumulative time (min)

Acc

umul

ativ

e in

take

(cm

)


33

(cm), h(ti) is the water level in hole at initial time ti (cm), h(tn) is the water level in

hole at final time tn (cm) and 864 is used to convert into m d-1.

The k value was 0.03 m per day, which falls within the very slow conductivity class

according to the classification of Landon (1991). This result corresponds to the value

of indicative hydraulic conductivity for clayey soils with the prismatic or angular

blocky structure observed in profile pits P2 and P3.

The very slow hydraulic conductivity of the soils is perhaps due to the effect of the

Na+ ions in the soils. The soil structure has been broken down into finer particles,

which slows down the permeability of soils to water and air. The organic matter that

helps to maintain the aggregates of soils has been dispersed by the Na+ ions. The

black colour of dispersed soil particles was observed in the surface layer, which

indicates the effect of Na+ ions in degrading the soil structure.

4.2.2. Soil chemical properties of the Shemshemia area

Soil chemical properties indicate the status of the soil in terms of whether it is acid or

alkaline, its content of soluble salts, capacity to hold cations, content of cations and

anions, important plant nutrients such as nitrogen and phosphorus, organic matter and

carbonate. Overall, these properties will give a strong indication as to the fertility

status of the soil in terms of its ability to provide essential nutrients to plants/crops,

and to the favourability of the soil chemical environment for plant growth, i.e.

whether it is too acidic, too alkaline, too saline or too sodic, all of which would

negatively affect plant growth.

There are 13 essential mineral nutrients required by plants for growth. Those required

in the largest amounts are the macronutrients, of which three are the most important

and are classed as major nutrients. These are nitrogen (N), phosphorus (P) and

potassium (K) and are usually added as fertilisers for all crops on most soils. Three

further macronutrients, sulphur (S), calcium (Ca) and magnesium (Mg), are known as

the secondary nutrients, and may be added in fertilizers for some crops on some soils

where their availability is naturally low. The remaining seven nutrients are required

in smaller quantities, although they are still essential for growth, and are known as

micronutrients. These are iron (Fe), manganese (Mn), zinc (Zn), copper (Cu),

molybdenum (Mo), chlorine (Cl) and boron (B). They are usually not added as

fertilizers since they are naturally available in most soils in sufficient quantities. In


34

some soils with particular chemical properties, however, there may be deficiencies in

certain micronutrients.

The full results of the soil chemical analysis are shown in Annex B, (Tables 1 to 7).

The samples have been divided into four groups for the sake of comparison: samples

from rainfed sites, salt-affected (sodic) sites (uncultivated), irrigated sites, and the

riverbank. Annex B, Table 1 shows the complete set of results for all soil samples

and Annex B, Table 2 shows a statistical summary of the results for all samples and

for each group separately. Annex B, Table 3 shows the chemical analysis for the

topsoil samples only, and Annex B, Table 4 the statistical summary for the topsoil

samples. Annex B, Tables 5 and 6 respectively show the statistical information for

the subsoil samples. Annex B, Table 7 shows the results of a correlation analysis

between the various chemical properties to indicate which properties are related to

each other. The chemical properties are described in the following sections for

irrigated soils and then for the non-irrigated (rainfed, sodic and river bank) soils.


35

Table 4.11. Summary of Chemical Analysis of Shemshemia Soil Samples ?????? Sites Depth pH EC Exchangeable cations CEC Base ESP* OM N P Anions CaCO3

dS/m Ca2+ Mg2+ K+ Na+ Total me/100g saturation % % % mg/kg Cl- CO32- HCO3

- %

me/100g % mg/l

All samples Average 8.7 1.27 24.8 4.3 0.43 6.62 36.1 38.5 97 15.6 1.15 0.022 14.8 113 80 183 2.38

Topsoil 8.7 1.87 22.8 3.8 0.44 5.18 32.2 35.7 95 14.0 1.27 0.024 18.3 125 77 162 2.14

Subsoil 8.8 0.76 26.4 4.7 0.43 7.84 39.4 40.8 99 17.0 1.05 0.020 11.9 103 82 201 2.59

Rainfed Average 8.4 0.20 29.3 5.9 0.58 1.07 36.8 42.0 89 3.1 0.99 0.011 8.9 84 60 146 2.67

Topsoil 8.4 0.17 28.3 5.4 0.57 1.12 35.3 40.4 89 3.3 1.06 0.012 10.7 96 60 153 2.68

Subsoil 8.4 0.22 30.1 6.2 0.59 1.04 37.9 43.1 89 3.0 0.94 0.010 7.7 76 60 142 2.66

Sodic Average 9.3 2.84 23.2 3.4 0.35 13.35 40.3 41.0 104 30.8 1.13 0.022 17.7 159 105 232 2.92

Topsoil 9.3 4.22 21.5 3.5 0.37 10.25 35.7 41.8 89 26.2 1.13 0.023 22.6 198 100 201 2.63

Subsoil 9.4 1.23 25.1 3.4 0.32 16.96 45.7 40.2 120 36.1 1.13 0.020 12.1 114 110 270 3.25

Irrigated Average 8.2 0.24 23.9 4.4 0.44 1.75 30.5 33.0 95 5.7 1.28 0.025 14.1 82 60 116 1.97

Topsoil 8.2 0.23 22.7 3.7 0.48 1.73 28.6 29.9 101 5.7 1.39 0.027 16.3 70 60 131 1.72

Subsoil 8.2 0.24 24.9 4.8 0.41 1.77 31.9 35.4 90 5.6 1.20 0.023 12.4 92 60 105 2.18

Riverbank Average 9.5 1.78 28.3 4.9 0.51 12.69 46.4 50.7 95 23.8 0.86 0.023 16.0 123 100 386 1.77

Topsoil 8.4 0.32 21 3 0.313 1.97 26.28 24.0 109 7.5 1.86 0.030 17.3 53 60 122 0.56

Subsoil 10.1 2.51 32.0 5.8 0.62 18.05 56.5 64.1 88 32.0 0.37 0.020 15.4 158 120 519 2.38


36

a) Soils of the irrigated areas

Soil pH indicates whether the soil is acidic, neutral or alkaline. Plants and soil micro-

organisms show a marked response to soil reaction since it has a major influence on the

soil chemical environment and on the availability of essential nutrients. Plants tend to

prefer a soil pH just below to just above pH 7 (neutral). When pH becomes too acidic or

too alkaline a range of problems occur, including deficiencies in the availability of various

nutrients and direct toxicity.

The irrigated soils in Shemshemia show a soil reaction ranging from 7.7 to 8.6, with an

average of 8.2, indicating slight to moderate alkalinity. Soils of arid and semi-arid regions

are commonly alkaline due to an accumulation of carbonates in the soil (Maskey, 1984).

The pH of the Shemshemia soils is slightly high for optimal plant growth.

Calcium carbonate contents ranged from 0.56 to 3.70% with an average of 1.97%. This

indicates a slightly calcareous soil.

Salinity and Exchangeable Sodium Percentage Salinity refers to the total concentration of all salts in the soil. The salts are usually

chlorides, sulphates, carbonates and bicarbonates of calcium, magnesium, sodium and

potassium. High concentrations of soluble salts are detrimental to plant growth particularly

because water availability is reduced, as well as due to direct toxicity from some ions such

as sodium and chloride, and ionic imbalances created in the plants. Salinity is a common

problem in arid and semi-arid areas, particularly where irrigation with water containing

dissolved salts is practised, due to the fact that as water evaporates from the soil surface the

salts remain in the soil and accumulates over time (FAO, 1988). Salts dissociate into

positive and negative ions in solution and therefore have the ability to conduct an electric

current. Salinity is therefore measured as electrical conductivity of a saturated soil extract

or paste (ECe), where the soil:water ratio is 1:2 (in this case a ratio of 1:2.5 was used). A

soil is classified as saline if it has an ECe value of 4.0 or more d S m-1, although some

plants, particularly for example fruit and vegetable crops, are sensitive to lower salinity

levels down to 2.0 d S m-1 (Landon, 1991).

The irrigated soils of the Shemshemia show and EC values ranging from 0.05 to 0.93 d S

m-1, with an average of 0.24 d S m-1. These are very low salinity levels indicating that the

soils have neither a significant input of salts from their parent materials or from the water

used for irrigation, and that the crops are unlikely to be affected.

Soils containing sodium salts have particular problems since high levels of sodium ions


37

(Na+) cause clays to disperse, which breaks down the soil structure, decreases porosity and

lowers the permeability of the soil to water and air. High levels of sodium are also

associated with high alkalinity. The exchangeable sodium percentage (ESP) gives a

measure of the potential sodium problem, and is the percentage of sodium ions out of the

total base cations (Ca2+, Mg2+, K+ and Na+) or total cation exchange capacity (CEC) of the

soil. The CEC is a measure of the total number of cations (positive ions) that a soil can

hold. If the ESP is more than 15% and it is also associated with a high pH (of 8.5 or more)

then the soils are classified as sodic.

The irrigated soils in Shemshemia have an average ESP of 5.7% with most sites showing a

much lower value, indicating that there is no sodicity problem. However, site A2 shows

19.0% and 20.4% ESP and site A3 shows 9.7 and 14.0% ESP in the topsoil and subsoil

respectively. The soil pH for A2 is below 8.5 but for A3 is 8.4 and 8.6 for topsoil and

subsoil respectively. These values indicate that sodicity problems spread beyond the

uncultivated area into some of the irrigated areas, which are nearer to the observed non-

irrigated sodic area.

Cation Exchange Capacity, Exchangeable Cations and Percent Base Saturation Negatively charged surfaces on clay particles and humus molecules (decomposed organic

matter) in the soil attract cations (such as Ca2+, Mg2+, K+) and hold them in the soil,

where they are available to plants. The Cation Exchange Capacity (CEC) is used as one

way of estimating soil fertility. Soils with a high value of CEC are considered fertile, and

vice versa. In general, CEC ranges from a minimum of 2 meq 100 g-1 soil in sands up to a maximum

of 60 me 100 g-1 in clay soils (Brady, 1991). The soil textural class of non- irrigated soils in

Shemshemia is loams, with more or less equal proportions of sand, silt and clay (Table

4.9). The irrigated soils have CEC contents ranging from 14.8 to 44.9 me 100 g-1 soil with

an average of 33 me 100g-1.

Exchangeable Cations

Calcium (Ca2+) is a secondary macronutrient required by plants and is a major component

of cell walls and is important for root growth, especially root tips. Calcium deficiency

causes poorly developed roots with weak tips, and distorted leaves with hooked tips and

curled margins. Calcium is also beneficial in the soil due to its role in soil structure

stabilisation and combating soil sodicity. Calcium is the dominant cation in all the soil

samples from Shemshemia. The irrigated soils contain between 14 to 39 meq Ca2+ 100 g-1


38

soil or 23.9 meq 100g-1 on average, which is 78% of the total base cations. This is high, as

is usual in neutral to alkaline soils.

Magnesium (Mg2+) is another secondary macronutrient required by plants and is vital for

chlorophyll production and is important in most enzyme reactions. Magnesium deficiency

causes different symptoms in different plants, but commonly includes leaf yellowing with

brilliant tints. Leaves may suddenly drop off without withering. Symptoms show first on

older leaves. The irrigated soils in Shemshemia contain between 2 to 7 meq Mg2+ 100g-1

soil, with an average of 4.4, or 14% of the total base cations. This gives a Ca:Mg ratio of

5.4:1, which means Mg becomes increasingly unavailable with increasing Ca. Calcium and

magnesium ions make up 92% of the total exchangeable base cations, which is usual in

neutral to alkaline soils. The magnesium contents are classed as very high (which requires

a magnesium content of >1.48 meq 100 g-1).

Potassium (K+) is one of the three major macronutrients required by plants and promotes

general vigour, disease resistance and sturdy growth. Potassium deficiency causes stunted

growth with leaves close together. Starting with the older leaves, the leaf tips and edges

turn scorched brown and leaf edges roll up. The irrigated soils in Shemshemia contain 0.15

to 0.92, on average 0.44, meq K+ 100g-1 soil, or 1.4% of the total base cations. These

values indicate variable K+ availability for plant growth. Soils with K+ contents at the low

end of the range are classed as having a low K+ content and crop yields are expected to be

50-80% of the yield that could be obtained with adequate fertiliser application. Soils with

K+ contents at the high end of the range are classed as having very high K+ contents and do

not need fertiliser applications. As a general guide, those soils with less than 0.45 me K+

100 g-1 would benefit from fertiliser application of K+. Table 4.13 indicates the rating for

some of the soil nutrients.

Table 4.12. Rating of soil nutrients in relation to expected crop yield.

Supply

class

Expected relative

yield without

Rating of exchangeable bases

fertiliser K+ Mg2+ Ca2+ Na+

(%) me 100g-1

Very low 50 0.1 < 0.5 < 2 < 0.1

Low 50-80 0.1-0.3 0.5-1.5 2-5 0.1-0.3

Medium 80-100 0.3-0.6 1.5-3.0 5-10 0.3-0.7

High 100 0.6-1.2 3-8 10-20 0.7-2.0

Very high 100 >1.2 >8 > 20 > 2

Source: ILACO, (1989).


39

Sodium (Na+) is not a nutrient required by plants, and instead, when present in high

concentrations, causes a range of problems for plant growth. The contents of sodium in the

irrigated soils vary between 0.17 and 5.78, with an average of 1.75, meq Na+ 100g-1 soil,

or 5.7% of the total base cations. However, it is not the actual content of sodium that is

most important, but its relative amount compared to other cations, and this has already

been mentioned earlier as the exchangeable sodium percentage (ESP). Percent Base Saturation (PBS) is the percentage of base cations out of the total CEC of

the soil. In neutral to alkaline soils base cations make up most of the CEC, but as soils

become more acidic H+ and Al3+ become increasingly dominant. The irrigated soils give a

PBS range of 60-144%, with an average of 95%.

Organic matter, Nitrogen and Phosphorus Organic Matter (OM): Organic matter in soils consists primarily of plant remains in

various stages of decomposition, soil microorganisms and humus (complex, relatively

stable organic molecules formed during decomposition processes). Soil organic matter is

very important in binding soil particles together, thereby aiding soil structure development

(and consequently improving water infiltration, aeration and root development) and

increasing resistance to erosion. It is also able to absorb up to 20 times its own weight of

water, thereby increasing water retention in the soil, which is very useful in arid and semi-

arid climates. Organic matter also contains some of the most important plant nutrients such

as nitrogen, phosphorus and sulphur, and attaches cations such as calcium, magnesium,

potassium and ammonium to its negatively-charged surfaces. It therefore acts as a source of

all of the plant macronutrients in the soil.

In the irrigated soils, OM content varies between 0.54 to 2.18%, with an average of 1.28%.

This is very low, and unfortunately, this is commonly the case for soils of arid and semi-

arid regions probably due to the sparse vegetation cover. Several studies have indicated

organic matter contents in Eritrean soils of less than 1% (Maskey, 1984). The irrigated soils

contain a slightly higher OM content compared to the non-irrigated soils in Shemshemia,

probably due to the better vegetation growth and fertilisation under irrigation.

Nitrogen is a major plant macronutrient, stimulating leaf and stem growth. Nitrogen

deficiency causes reduced growth and pale yellowish green leaves. The older leaves turn

yellowish first since the nitrogen is readily removed from the old leaves to the new growth.

Nitrogen content of soils is usually correlated with OM content since over 90% of the

nitrogen found in soils are in an organic form. Table 4.7 in Annex B shows this to be the


40

case where a highly significant correlation was found between the two properties. The total

nitrogen contents of the irrigated soils range from 0.01 to 0.05% (with an average of

0.03%) which are low values.

The average OM content of 1.28 can be converted to the soil organic carbon (OC) content

by dividing by 1.72. This gives an average OC content of 0.74%. The average C:N ratio

can then be calculated as 0.74 : 0.03 or 25:1. This C:N ratio is outside the common range in

arable soils of 8:1 to 15:1 in the upper 15 cm, again demonstrating the very low content of

nitrogen in the soils (Brady, 1990).

Phosphorus is another major plant macronutrient. It is important for the germination and

growth of seeds, the production of flowers and fruit and the growth of roots. Phosphorus

deficiency causes reduced growth and small leaves that drop early, starting with the oldest

leaves. Leaf colour is a dull, bluish green that becomes purplish or bronzy. Leaf edges often

turn scorched brown. The available phosphorus content of the irrigated soils in

Shemshemia ranges from 2.8 to 31.4 mg kg-1, with an average of 14.1 mg kg-1. These

indicate highly variable contents ranging from very low to very high (see Table 4.11), with

the average content being medium. Soils with less than 17 mg/kg of phosphorus would

benefit from the addition of P-containing fertilisers. Maximum phosphorus availability

occurs between pH 6.0 to 7.5, and so those soils with higher pH may be expected to show

phosphorus deficiency.

Soluble anions: These include chloride (Cl-), carbonate (CO32-), and bicarbonate (HCO3

-).

The irrigated soils contain lower concentrations of all three anions compared to the non-

irrigated soils. High Cl- concentrations would be expected in more saline soils, and high

CO32- and HCO3

- concentrations in more alkaline soils.

b) Soils of the (currently) non-irrigated areas Soil pH and calcium carbonate: The rainfed sites have an average soil pH of 8.4, the

sodic soils have 9.3 and the soils along the riverbank have 9.5. The pH of the rainfed sites

ranges from 8.2 to 8.6. This is on average slightly higher than the irrigated sites but the

rainfed areas do not show extreme alkalinity. Both the sodic and riverbank sites, however,

show maximum soil pH values of 10.3, and their average values are also very high. This

indicates an alkalinity problem in these areas and plant growth would be seriously affected.

Calcium carbonate contents averaged 2.67% in rainfed areas, 2.92% in sodic areas and

1.77% on the riverbank. These values do not very significantly from the irrigated soils and

indicate slightly calcareous soils with no detrimental effects on plant growth.


41

Salinity and ESP: Salinity levels are very low in the rainfed areas, ranging from only 0.11

to 0.26 d S m-1. This is very slightly less, on average, than in the irrigated soils. In the sodic

areas, however, the EC ranges from 0.29 to >20 d S m-1 with an average of 2.84 d S m-1.

The upper value is very high and somewhat questionable, and the results for individual

samples show that most soils have an EC <2.0 d S m-1. The sodic soils have a higher salt

content than the irrigated and rainfed soils but cannot be classified as saline soils. The

riverbank samples show a very low salinity in the upper and deep horizons but a high salt

content (about 4.3 d S m-1) at a depth of 30-80 cm.

The ESP for the rainfed sites is low, on average only 3.1%, but the sodic sites show an

average ESP of 30.8%, an extremely high value. This clearly indicates the nature of the salt

problem in the area. It is the highest sodium content in the soils, not a high soluble salt

content. Two of the soil samples in the sodic area (from the surface layer) have ESP values

of 4.3 and 9.9, which strictly does not classify them as sodic soils, but all other samples

have ESP values of at least 16.6%, and most well over 30%. The average ESP value for the

topsoil samples is 26.2% and for the subsoil samples 36.1%, indicating that the sodicity

problem increases with depth. These soils also have an average pH of 9.3 and so are

classified as true sodic soils.

The riverbank site also shows a sodicity problem, with an average ESP of 23.8%, but ESPs

of more than 30% below 30 cm depth. The riverbank samples also have an average pH of

9.5, and so this site is also classified as a sodic soil.

CEC, Exchangeable cations and PBS: The CEC of the rainfed sites ranged from 36.6 to

47.0, with an average of 42.0 meq 100 g-1 soil. This is a narrower and higher range than for

the irrigated soils. The sodic areas in the topsoil and subsoil depth have a similar average

CEC of 41.0 but a much wider range (from 25.1 to 60.9 meq 100 g-1), and the riverbank

samples also have a high average CEC of 50.7 me 100 g-1. According to the rating of CEC

by Landon (1991), the soils in general all have very high CEC values indicating adequate

concentrations of cations.

Exchangeable cations Calcium: The calcium contents in the rainfed sites and on the riverbank are slightly higher

on average than in the irrigated soils, but in the sodic areas it is similar to the irrigated

soils. In all soils, calcium is the dominant cation, making up 80% of the total CEC in the

rainfed soils. Whereas, about 60% in the sodic and riverbank soils, reflecting the larger

proportion of sodium in these samples.


42

Magnesium: Magnesium contents in the rainfed and riverbank sites are slightly higher

than those in the irrigated soils, but are slightly less in the sodic area. Even the lowest

content of 2.0 me 100 g-1, however, is classed as high (see Table 4.12). And this indicates

no shortage of magnesium for plant growth.

Potassium: As with magnesium, potassium contents in the rainfed and riverbank soils

(0.58 and 0.51 me 100 g-1 on average respectively) are slightly higher than in the irrigated

soils, but the sodic soils (0.35 meq 100 g-1) measured slightly lower potassium contents.

The soils show variable contents, however, and as already mentioned any sites with less

than 0.45 me 100 g-1 potassium would benefit from fertiliser additions.

Sodium: The sodium contents in the rainfed sites are lower on average and in range than in

the irrigated soils, being at maximum only 6.1% of the total base cation content. There is a

very clear difference, however, in the sodic and riverbank areas, where sodium clearly

makes up a high percentage of the CEC, and this has already been mentioned as the main

problem in these areas.

Percent Base Saturation: The Percent base saturation is high in all soils, which was above

47%.

Organic matter, Nitrogen and Phosphorus: The organic matter content of the rainfed

soils was on average only 0.99%, which is low. This is to be expected in dry soils where

vegetation cover for most of the year is low. The riverbank also has a low OM content of

0.86% on average. The soils in the sodic area had an average OM content of 1.1%, slightly

less than in the irrigated areas. In general, of course, all the soils in the area have low

amounts of OM and would definitely benefit from an increased input of organic materials

(maybe from crop residues or animals manure depending upon availability).

Nitrogen: The total nitrogen contents are low, even less than in the irrigated soils, ranging

from 0.01% in the rainfed soils to 0.02% on average in the sodic and riverbank areas. This

gives a C:N ratio of 58:1 in the rainfed soils, 33:1 in the soils of the sodic area and 50:1 in

the riverbank samples. All these C:N ratios are clearly outside the common range of

tropical soils (i.e. 8:1 to 15:1). The soils are in need of additional nitrogen.

Phosphorus: The phosphorus contents in the rainfed soils range from low to medium, and

so all soils in this area would benefit from additions of phosphorus fertilisers. The


43

soils of the sodic area contain the highest P contents on average, ranging from low to very

high. Any soils with less than 18 mg kg-1 P would benefit from fertiliser additions (Landon,

1991).

Soluble anions: These include chloride (Cl-), carbonate (CO32-), and bicarbonate (HCO3

-).

The rainfed soils contain low concentrations of all three anions, similar to the irrigated

soils. Whereas, soils of the sodic and riverbank areas contain noticeably higher

concentrations of all anions.

4.3. PROBLEM SOILS IN THE SHEMSHEMIA AREA

For optimal plant growth, a soil must possess a range of favourable physical, chemical and

biological properties. Physical properties include soil texture and structure. Texture refers

to the range of particle sizes present in the soil and should ideally be a loam, or sub-class of

loam, where all particle sizes are present in some quantity. Structure refers to the

arrangement of the particles and affects aeration and water infiltration. With a suitable

proportion of small aggregates (particularly in the surface layers), and large and small

pores, water and air will be able to move easily through the soil, maintaining a well-

aerated, moist environment. Plant roots will also be able to grow unhindered by compacted

layers. From a chemical point of view, the soil must be able to supply the full range of

plant nutrients in the required amounts. It must also have no adverse chemical properties

such as excess acidity, alkalinity, salinity or sodicity, nor contain high concentrations of

harmful chemical components such as heavy metals. It is also beneficial for a soil to

support a healthy, diverse population of soil micro-organisms, which breakdown plant

residues, fix nitrogen, and generally improve the supply of nutrients to plants.

The main soil problems in Shemshemia are (1) sodicity (high sodium content), (2)

alkalinity (high pH), (3) poor structural development, (4) low infiltration rates and (5) low

content of some macronutrients, notably nitrogen throughout the area.

Points 1 to 4 all relate to the sodium content of the soil and will be discussed below. Points

5 and 6 are additional problems that the farmers should address to get the best yields from

the soils. It is advisable to add fertilisers to redress the nitrogen and phosphorus contents in

some parts of the farm. It is also advisable to increase the organic matter content of the

soils by adding crop residues or animal manure.


44

4.3.1. Characteristics of the sodic soils (black alkaline soils) in Shemshemia

Sodic soils are characterised by high sodium content, low soluble salt content, and high pH.

Exchangeable sodium content must be at least 15% of the total cation exchange capacity

(CEC). In soils with high pH, the CEC is occupied mostly by base cations (Ca2+, Mg2+, K+,

and Na+) with a very small amount of other cations (Al3+, H+ and NH4+). The exchangeable

sodium percentage (ESP) was therefore calculated as a percentage of the total base cations

present rather than a percentage of the CEC. The sodic soils in Shemshemia measured an

ESP of 30% on average compared to only 3% and 6% for the rainfed and irrigated areas,

respectively.

Sodic soils have a high pH of more than at least 8.5, and even as high as pH 10. The

average pH for the sodic soils in Shemshemia was 9, with a maximum of 10. High pH is

associated with the presence of sodium bicarbonate (NaHCO3) and sodium carbonate

(Na2CO3), which are readily soluble in water. Sodium-rich clays, HCO3- and CO3

2- react

with water to form hydroxyl (OH-) ions that cause high pH (FAO, 1988).

The soluble salt content of the sodic soils (in Shemshemia farm) is 2.8 d S m-1 on average,

which is less than the required 4 d S m-1 for the soils to be classed as saline soils.

4.3.2. Effects of sodicity on soil properties

The positively charged sodium ions become attached to the negatively charged surfaces of

the clay particles in the soil. As a result, the clay particles lose their tendency to stick

together when wet. The clay particles are dispersed and block soil pores and the soils

become dense and compacted and impermeable to both water and roots. The infiltration

rate and hydraulic conductivity of the soil decreases to the extent that little or no water

movement occurs (Figure 4.1). Water remains on the surface of the soil for a long time

after rainfall or irrigation. This also leads to poor aeration of the soil. The soil is plastic

when wet and becomes hard and brick–like when dry and tillage becomes difficult.

Because the clay particles do not stick together, the soils also become structurally unstable

and are more susceptible to water and wind erosion. The high alkalinity associated with

sodicity cause soil organic matter to disperse, which further weakens soil structure. Surface

crusting is a common problem in cultivated sodic soils. Sodic surface layers are highly

prone to erosion because of the low aggregate stability and are easily detached by raindrop

impact. When dry, the surface soils in sodic sites forms a hard crust (Seelig, 2000).


45

4.3.3. Effects of sodicity on plant growth

Root growth and seedling emergencies are restricted in the compacted and crusted sodic

layers with dispersed clays. Poor aeration due to poor drainage will reduce the oxygen

available to plant roots for respiration and will also cause carbon dioxide to build up in the

soil, both further restricting root growth.

The high pH often causes deficiencies in various plant nutrients, particularly phosphorus

and micronutrients such as iron, manganese, zinc, copper and cobalt, all of which are much

less available when pH is greater than 7.0.

Sodium ions and anions such as bicarbonate are directly toxic to most plants. The caustic

influence of high pH affects plant growth. Live roots were seen to be vulnerable to

deterioration when pH was above 9.5 in sodic soils in North Dakota, USA (Seelig, 2000).

4.4. RECLAMATION & MANAGEMENT OF THE SODIC SOILS

4.4.1. Chemical methods for soil amendments

The development and maintenance of successful irrigation projects involve not only the

supplying of good irrigation water quality to the land but also the control of soil problems

(such as sodicity problems) in the fields.

Basically, reclamation or improvements of sodic soils requires the removal of part or most

of the exchangeable sodium and its replacement by the more favourable calcium ions in the

root zone. For quick results, cropping must be preceded by the application of chemical soil

amendments followed by leaching for removal of salts derived from the reaction of the

amendment with the sodic soils.

The kind and quantity of a chemical amendment to be used for replacement of

exchangeable sodium in the soils depend on availability of the amendment, the soil

characteristics (including the extent of soil deterioration), the desired level of soil

improvement, the crops intended to be grown and economic considerations.

The chemical amendments used for sodic soil reclamation include gypsum (CaSO4.2H2O),

calcium chloride (CaCl2.2H2O), acids or acid forming substances (e.g.H2SO4, S, FeSO4,

etc.) and ground limestone (CaCO3).

a) Lime (CaCO3) is an effective amendment only in soils having pH<7 because its


46

solubility rapidly decreases as the soil pH increases (FAO, 1988).

b) Calcium chloride (CaCl2.2H2O) is a highly soluble salt, which supplies soluble calcium

directly. Because of its high solubility in water, calcium chloride is the most readily

available source of calcium but it has rarely been used for reclamation (on an extensive

scale) because of its high cost.

c) Acids and/or acid forming substances (like sulphur and pyrite) are relatively slow

acting, because they must first be oxidised to sulphuric acid by soil micro-organisms before

they are available for reactions. Moreover, the soils should contain appreciable amount of

lime to react with the acids to form gypsum.

d) Gypsum is by far the most widely used amendment for reclaiming sodic soils because of

its abundant availability, replaces the sodium ions with calcium ions in the soil exchange

sites, low cost and easy application. Moreover, gypsum application improves soil

properties by providing calcium ions for plant nutrients and keeps the soil particles

flocculated.

The replacement of Na+ by Ca2+ in the gypsum can be presented in the form of chemical

equation as follows:

2Na+ + CaSO4 Ca 2+ + Na2SO4 [2]

Hence on the basis of soils characteristics, crops to be grown (i.e. citrus crops which are

sensitive at low ESP), cost of amendments and availability of the chemical amendment,

gypsum is recommended to reclaim the sodic affected lands in the Shemshemia farm.

Replacement of each mole of adsorbed sodium per 100 g soil will require half a mole of

soluble calcium as shown in Eq.[2].

1 mole of Na+ ion (23 g) would exchange with ½ mole of Ca2+ ion (20g)

To replace 1 centi-mole (cmole) of Na+ kg-1 soil = 20/100 = 0.2 g Ca2+ kg-1 soil

= 0.2 × 2.24 × 106 (mass of soil in 15 cm depth)

= 448,000g = 448 kg

= CaSO4.2H2O = 172

Ca2+ 40

= 4.3 × 448 kg

= 1,926 kg (1.93 tons) of pure gypsum ha-1

Micelle Micelle


47

The quantity of pure gypsum required to supply half a cmole of calcium per kg soil for the

upper 15 cm soil depth will be 1,926 kg (1.93 tons) of pure gypsum ha-1 15 cm-1 depth.

Therefore, to replace the exchangeable Na+ of 10 meq 100g-1 soil (in the average topsoils

of the sodic areas), about 20 tons of pure gypsum per ha should be applied in Shemshemia

farm. The total gypsum requirement for 5 ha sodic land will then be about 100 tons of pure gypsum. This figure, however, should be used with caution because the effectiveness

of gypsum in replacing the Na+ ions should be tested in the field.

Gypsum is normally applied broadcast as a dry powder and then incorporated into the soil

by means of disking or ploughing. From the standpoint of efficiency in replacing

exchangeable sodium, it is advantageous to leach most of the soluble salts out of the soil

before applying chemical amendments. In other words, one irrigation prior to application of

gypsum would further ensure leaching of soluble carbonates, which are found in many

sodic soils. This leaching eliminates the need of additional quantities of gypsum for

neutralising the free sodium carbonate.

4.4.2. Physical and biological methods for soil amendments

a) Deep ploughing: Since the sodic profiles (in Shemshemia farm) have dense subsoil

layers, this soil should be chiselled to a depth of 1 m in order to breakdown the hard layer.

This will facilitate the movement of water ease to the lower layers and also plant roots can

readily proliferate in the zone of water and nutrients availability, which eventually

improves crop yields. Deep ploughing up to 100 cm has been reported to be a useful

practice for improving sodic soils with hardpans or dense clay subsoil layers (Rasmussen et

al., 1972).

However, deep tillage using chiselling and/or subsoiling implements should only be

performed when soils are dry enough to shatter and crack. If done wet, compaction,

aeration and permeability problems can be expected (FAO, 1985).

b) Organic residues: Animal manure, crop residues in conjunction with inorganic

amendments (like gypsum) could be applied to reclaim the sodic soils in Shemshemia

farm. Organic manure (like farmyard manure, animal manure) has long been known to

facilitate the reclamation of sodic soils by lowering of pH, replacing the exchangeable Na

by Ca and/or Mg and thereby lowering the ESP (Yadav and Agarwal, 1961; Kanwar et. al.,

1965).

c) Crop selection: Growing crops such as cotton, tomatoes or grass sp. (which are


48

tolerant to semi-tolerant to ESP) or selection of tolerant rootstocks (which exclude Na+

ions from absorption) offer a practical solution to control soil sodicity problems in

Shemshemia farm. On the other hand, citrus crops are not recommended to grow on sodic

lands because of their extreme sensitiveness even at low ESP values (i.e. ESP = 2-10).

4.4.3. Socio-economic considerations

Reclamation of sodic soils requires application of amendments. For a technology to be

sustainable, it should, however, be socially acceptable, economical feasible and

environmentally sound.

The social and economic considerations should be taken into account when recommending

the chemical, physical and/or biological amendments to reclaim the sodic lands in

Shemshemia farm. These considerations include the availability of the amendments (to the

farmers) at a reasonable cost, the institutional finances available, marketing facilities if new

crops are to be introduced. In addition, on-the-job training about the principles of soil

amendments and the application methods in the field should be given to the farmers in

Shemshemia area.

Table 4. 12. The cost of gypsum application per ha and total cost (for 5 ha sodic land) at Shemshemia farm.

Activities Cost ha-1

nakfa †

Total cost

nakfa

Ploughing 228.00 1,140.00

Harrowing

Diesel for motor pump

45.00

100.00

180.00

500.00

Labour for watering‡ 20.00 100.00

Labour for ploughing‡ 100.00 500.00

Gypsum application§ 27,000.00 135,000.00

Total 27,493.00 137,420.00

† nakfa is a local currency of Eritrea. The exchange rate is 1 US = 13.50 nakfa in 2002.

‡ 1 labour cost = 20 nakfa per day

§ gypsum application for 20 tons ha-1 (estimated cost 10 US per ton of gypsum)

Table 4.12 shows estimated cost of gypsum application (exclusively of transport cost) to

reclaim the 5 ha sodic land in Shemshemia farm. Assuming the indicative annual yield of

orange fruits under smallholder production as 20 tons ha-1 (Landon, 1991) and the price of

1 ton orange fruit as 10,000 nakfa (about US $750), the total income will be 200,000 nakfa

(about US $15,000) per ha. This indicates that the total income from the citrus farm is

above the cost of gypsum application and other farm activities (Table 4.13). Therefore, it

seems economically feasible if citrus plants (such as orange) are planted after the

reclamation of the sodic land unit in the Shemshemia farm.


49

4.5. CHECKLIST FOR PREVENTION OF NON-SODIC AREAS

Table 4.13. gives the prevention methods for unaffected sodic lands in Shemshemia farm.

Table 4.12. Checklist for prevention of non- sodic areas in Shemshemia farm.

Prevention methods Remarks

Frequent light irrigation • Solution favours the adsorption of calcium and

magnesium over sodium ions.

• Losses of calcium due to precipitation will be minimum.

Timing of irrigation • Irrigation should often proceeds or follows planting.

Slowing evaporation rate • Retard the translocation of upward movement of soluble

salts.

Changing irrigation methods (from

furrow to drip irrigation system) • Saves water and labour

• Increasing infiltration

Cultivation and deep tillage • Improves penetration of roots and infiltration of water

• Breaks up the compacted subsoil layer

Using organic residues • Incorporating crop resides into the soil improves water

infiltration and soil physical fertility (like soil structure).

Growing tolerant crops • Crops such as sorghum, tomatoes, cotton, etc. (which are

adaptable to Shemshemia area) are tolerant to high ESP.

5. CONCLUSIONS

One of the main problems in the Shemshemia farm is the sodic soils in the non-irrigated

fields. This sodicity problem could be ameliorated using the chemical amendments (like

gypsum) with a combination of application of physical amendments (such as deep

ploughing and cultivation).

However, field trials should be conducted to test the soil amendments to control the

sodicity problems so that crop yield is improved to an extent that justifies the cost incurred

in the application of the amendments. In other words, the soil amendments to correct the

sodicity problems must be tested on a pilot project scale (at a plot level) before being

applied on a large scale in the Shemshemia farm.


50

The water quality of the river Gash, well water and canal water in the Shemshemia fields

have good water quality. The waters contain low concentration of salts and toxic elements,

which is safe to use for irrigation and drinking purpose. There is ample quantity of water to

irrigate the existing fields and further to expand irrigation schemes in the Shemshemia

area.

The causes of sodicity problems in the farm are not from the irrigation water source but

from the in situ weathering of the parent rock in the field. The parent rock consists of Na-

feldspar minerals (i.e.albite) which have weathered and increased the concentration of Na+

ions in the soil exchange complex.

On the other hand, the irrigated soils have good physical and chemical properties. They did

not show sodicity and/or salinity problems in their profile. The citrus crops in the irrigated

soils have good stand. Salinity and/or sodicity symptoms were not observed in the leaves of

the citrus plants.

Poor farm management and riverbank erosion also pose serious problems in the

Shemshemia irrigation scheme. These problems should be given due attention and the

possible solutions that are suggested in this report (Table 4.6) could be taken to address the

problems.


51

6. REFERENCES Brady, N. C (1990). The Nature and Properties of Soils. 10th ed. Collier Macmillan

publishers, London, UK.

FAO (1979). Soil survey, investigations for irrigation, FAO soils bulletin 42, FAO, Rome,

Italy.

FAO (1985). Water quality for agriculture. FAO irrigation and drainage paper 29 rev.1,

Rome, Italy, 174 pp.

FAO (1988). Salt-affected soils and their management. FAO soils bulletin 39, Rome, Italy,

131 pp.

FAO-UNSECO (1988). Soil map of the World, Revised legend with corrections. World soil

resources report 60. FAO, Rome, Itlay, 140pp.

FAO (1990). Guidelines for soil profile descriptions, 3rd edition. FAO, Rome, Italy, 70pp.

FAO (1994). Eritrea agricultural sector review and project identification, /annex 5, Rome,

Italy, pp3-4.

FAO (1997). Support to forestry and wildlife sub-sector, pre investment study report

TCP/ERI/6712 (F). Annex 5: Afforestation in Eritrea, FAO, Eritrea.

FAO-ISRIC (1998). FAO-ISRIC soil database (SDB), In: FAO, 1990. Guidelines for soil

profile descriptions, third edition. FAO, Rome, Italy.

HACH (1986). Water analysis handbook, HACH company, Colorado, USA.

ILACO, B.V. (1989): Agricultural compendium for rural development in the tropics and

subtropics, Elsevier, Amsterdam. Pp.51-195.

John, Ryan, Sonia Garabet, Karl H.armsen and Abdul Rashid (1996). A soil and plant

analysis: Manual adapted for the West Asia and North Africa region, ICARDA,

Aleppo, Syria.

Kanwar, J.L., Bhumbla, D.R. and Singh, N.T. (1965). Studies on the reclamation of saline

and sodic soils in the Punjab. Indian J. Agric. Sci. 35: 43-51. In: FAO (1988). Salt-

affected soils and their management. FAO soils bulletin 39, Rome, Italy.

Klute, A.(Ed) (1986). Methods of soil analysis: Physical and mineralogical properties of

soils, Agronomy no.9 (Part I) AM. Soc. of Agronomy, Madison, Wisconsin.

Landon, J.R. (1991). Booker tropical soil manual: A handbook for soil survey and

agricultural land evaluation in the tropics and subtropics, Longman, London, UK.

Maskey, R.B. (1984). Soils, their fertility and management in Eritrea. Univeristy of

Asmara, Asmara, Eritrea.

MoA (2000). Ministry of Agriculture annual report, Asmara, Eritrea.

MoME (1999). Gash Barka mapping and mineral exploration project, geology of

Dukumbia-Maikokah area, Asmara, Eritrea.


52

NCEW (1997). National Confederation of Eritreans Workers: Survey topographic map of

Shemshemia farm, Asmara, Eritrea.

Rasmussen, W.W., Moore, D.P. and Albasn, L.A. (1972). Improvement of a Solonetzic

(slick spot) soil by deep ploughing, subsoiling and amendments. Soil Sci. Soc. Amer.

Proc. 37: 137-142. In: FAO (1988). Salt-affected soils and their management. FAO soils

bulletin 39, Rome, Italy.

Seelig, B. D. (2000) Salinity and Sodicity in North Dakota Soils. North Dakota State

University Extension Service, EB 57.

World Bank Report (1994). Eritrea, options and strategies for growth: Vol II, report

no.12930 ER. Eritrea, Washington D.C., USA, Pp.59-89.

WRD (2000). Water Resources Department annual report, Asmara, Eritrea.

Yadav, J.S.P. and Agarwal, R.R., 1965. A comparative study of the effectiveness of

gypsum and dhaincha (Sesbania aculeata), J. Indian Soc. Sci. 9: 150-155. In: FAO

(1988). Salt-affected soils and their management. FAO soils bulletin 39, Rome, Italy.


53

ANNEXES ANNEX A: SOIL PROFILE DESCRIPTIONS

Profile - P1 Soil name (local): ‘terir hamed’ Mapping unit: Currently not irrigated soil Location: About 700 m west of Tekombia road Co-ordinates (UTM) 331899 E, 1638490 N Date: 010915 Authors: Mehreteab & Kiflemariam Topography: almost flat Land element: valley Irrigation: River Gash Slope: 2% Land use: Uncultivated land Parent material: In situ weathered Drainage class (FAO) Somewhat excessively drained Surface characteristic: None Moisture conditions: dry to 50 cm, moist below.

Depth (cm)

Horizon/Layer

Profile descriptions

0-26 Ap sandy loam, strong brown (7.5YR5/6,dry); grainy structure; the soil consistence is loose (d), friable (m), slight sticky (w); strong calcareous; abundant roots; clear lower boundary.

26-50 A1 Dry moisture statues; loamy texture; strong brown (7.5YR4/6); sub-angular blocky, weak developed structure; hard (d), slight friable (m), very slight sticky (w), extreme strong calcareous; fine, very few roots; defuse lower boundary.

50-150+

B Dry moisture statues; sandy loamy; strong brown (5YR5/8,d), strong brown (5YR4/6,m); dry (d), friable (m), nonstick (w) consistence; extreme strong calcareous; mineral nodules carbonate concrete;

Profile-P2 Soil name (local): ‘chew hamed’ Mapping unit: Currently not irrigated soil Location: About 200 m east of River Gash Co-ordinates (UTM) 331031 E, 1638266 N Date: 010915 Authors: Mehreteab & Kiflemariam Topography: almost flat Land element: valley Slope: 2% Land use: Uncultivated land Parent material: In situ weathered Drainage class (FAO) poorly drained

Depth (cm)

Horizon/Layer



54

0-24 A Dry loam soil; brown (7.5YR4/2d), dark brown (7.5YR3/2 m); sub angular blocky; hard (d), firm(m), sticky (w); very slight calcium carbonates; abundant roots; clear lower boundary.

24-57 AB Dry clay loam soil; dark brown (7.53/2 d), very dark brown (7.53/1 m); angular blocky; hard (d), firm (m), sticky (w); strong calcareous; carbonates mineral nodules; very few fine roots; defuse lower boundary.

57-82 B1 Moist silt loam; strong brown (7.54/6 d), brown (7.54/2 m); angular blocky weak developed; friable (m), sticky (w); slightly calcareous; very few, very fine, and faint mottles; clear to defuse lower boundary.

82-125 B2 Almost moist clay loam; strong brown (7.5YR4/6 d), brown (7.5YR4/3 m); sub angular weak developed; friable (m), slight sticky (w); very slight calcareous; abundant -few, fine size and prominent mottles; clear lower boundary

125-150+

B3 Moist loam; brown (7.54/4m, 7.5YR4/4w); sub angular weak developed; friable (m), slight sticky (w).

Profile – P3 Soil name (local): ‘tin hamed’ Mapping unit: Currently not irrigated soil Location: About 50 m east of citrus farm Co-ordinates (UTM) 331000 E, 1637940 N Date: 010916 Authors: Mehreteab & Kiflemariam Topography: almost flat Land element: valley Slope: 2% Land use: Uncultivated land Parent material: In situ weathered Drainage class (FAO) poorly drained

Depth (cm)

Horizon/Layer


0-35 Ap Dry clay loam; brown (7.5YR4/2, d) dark brown (7.53/2,w); sub angular blocky, poor developed; hard (d), friable (m), sticky (w); abundant roots; clear lower boundary.

35-100 B1 Moist clay loam; dark brown to very dark brown (7.5YR3/2 – 7.5YR2.5/2, m); hard (m), firm (w); very slight calcium carbonates; abundant, fine size, distinct mottles; defuse lower boundary.

100-150+

B2 Moist clay loam; dark brown to very dark brown (7.5YR3/2 - 7.5YR2.5/2 m); sub angular to prismatic; slight hard (m), sticky (w); medium calcareous; abundant –few, fine distinct mottles; few carbonates mineral nodules; few roots.

Profile -P4 Soil name (local): ‘duka hamed’ Mapping unit: Irrigated soil Location: About 100 m north of River Gash Co-ordinates (UTM) 331348 E, 1637592 N Date: 010916


55

Authors: Mehreteab & Kiflemariam Topography: Gently undulating Land element: valley Slope: 3% Land use: Irrigated citrus farm Parent material: In situ weathered Drainage class (FAO) well drained

Depth (cm)

Horizon/Layer


0-20 Ap Moist sandy loam; dark brown (7.5YR3/3,m); friable (m), abundant roots; defused lower boundary.

20-96 B1 Moist sandy loam; brown (7.5YR4/4 m); blocky, weak developed; friable (m); many, fine root; clear lower boundary; many termites are occurred in the layer.

96-128 B2 Moist clay loam; dark brown (7.5YR3/2,m); sub angular blocky, weak developed; friable (m), sticky (w); abundant, fine roots; clear lower boundary.

128-164+

BC Dry silt loam; brown (7.5YR4/4,d), dark brown (7.5YR3/3,m); sub angular blocky, developed; slight hard (d), friable (m), sticky (w); slight calcareous; few and fine roots


56

ANNEX B: SOIL PHYSICAL AND CHEMICAL DATA Table 1. Physical and Chemical Analysis of Shemshemia Soil Samples Table 2. Summary Statistics: All Samples. Table 3. Chemical Analysis of Shemshemia Soil Samples Topsoil Table 4. Summary Statistics for Topsoil Samples. Table 5. Chemical Analysis of Shemshemia Soil Samples: Subsoil Table 6. Summary Statistics for Subsoil Samples. Table 7. Correlation between soil chemical properties


57


58


59

Table 3


60


61

Table 5


62

Table 6 Table 7 ANNEX C. CHECKLIST QUESTIONNAIRE

1. Farmer’s name:

2. Gender: Male Female:

3. Education:

4. Place of origin:

5. How many people live in your household:

Boys:

Girls:

Wives:

6. Major source of income for the household:

a. b.

c. d.

7. When did the Shemshemia farm started?

8. What is the total area of land in tsimidi

9. Current land use appropriation in tsimidi for

Irrigated land:

Rainfed land:

Non- agricultural land:

10. What kind of crops do you grow?

11. What is the average crops yields?

Crops Yield (kg ha-1)

Sorghum

Orange

Lemon

Maize

Other (specify)

12. What is the type of the soil in the agricultural field?


63

a) Walka hamed:

b) Hutsa hamed

c) Duka hamed

d) Other, specify

13. Have you observed any salinity and/or sodicity problem in the field?

a) Yes

b) Not at all

c) Rarely

14. If yes, at what period of the year?

a) During the dry season

b) During the rainy season

c) All year round

15. Do you have the following water sources?

a) Well

b) River

c) Other, specify

16. How far is the nearest water source to you? kms.

17. Do you have water shortage to grow crops?

a) Yes

b) No

18. If yes, what do you suggest to alleviate water problems in the area?

a.

b.

c.

d.

e.

19. What are the main agricultural problems in your area? (in order of significance) apart from water

shortage?

a.

b.

c.

d.

e.

20. What are the possible solutions to these problems?

a.


64

b.

c.

d.

e.

21. What are the development potentials of the Shemshemia area?

a.

b.

c.

d.

e.

22. List five most severe development problems facing your area? (in order of significance) and suggest

possible solutions

Problems Solutions

1.

1.

2.

2

3.

3.

4.

4.

5.

5.

Thank you!


65

List of Publications: 1 A. Synnevåg, G. et Halassy, S. 1998: “Etude des indicateurs de la sécurité alimentaire dans deux sites de la zone d’intervention de l’AEN-Mali: Bambara Maodé et Ndaki (Gourma Malien)”, Groupe de Coordination des Zones Arides et Noragric, Agricultural University of Norway. 1 B. Synnevåg, G. and Halassy, S. 1998: “Food Security Indicators in Two Sites of Norwegian Church Aid’s Intervention Zone in Mali: Bambara Maoudé and N’Daki (Malian Gourma)”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 2 A. Aune, J.B. and Doumbia, M.D. 1998: “Integrated Plant Nutrient Management (IPNM), Case studies of two projects in Mali: CARE Macina programme and PIDEB”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 2 B. Aune, J.B. et Doumbia, M.D. 1998: “Gestion Intégrée de Nutriments Végétaux (GINV), Etude de Cas de deux projets au Mali: Programme de CARE Macina et PIDEB”, Groupe de Coordination des Zones Arides et Noragric, Agricultural University of Norway. 3 A. Berge, G., Larsen, K., Rye, S., Dembele, S.M. and Hassan, M. 1999: “Synthesis report and Four Case Studies on Gender Issues and Development of an Improved Focus on Women in Natural Resource Management and Agricultural Projects”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 3 B. Berge, G., Larsen, K., Rye, S., Dembele, S.M. et Hassan, M. 1999:“Rapport de synthèse et quatre études de cas sur Les Questions de Genre et Développement d’une Approche Améliorée concernant les Femmes et les Projets d’Agriculture et de Gestion des Ressources Naturelles”, Groupe de Coordination des Zones Arides et Noragric, Agricultural University of Norway. 4 A. Sydness, M. et Ba, B. 1999: “Processus de decentralisation, développement institutionnel et reorganisation des ONG financées par la Norvège au Mali”, Groupe de Coordination des Zones Arides et Noragric, Agricultural University of Norway. 4 B. Sydness, M. and Ba, B. 1999: “Decentralisation Process, Institution Development and Phasing out of the Norwegian Involvement in Mali”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 5. Waktola, A. and Michael, D.G. 1999: “Institutional Development and Phasing Out of the Norwegian Involvement, the Case of Awash Conservation and Development Project, Ethiopia”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 6. Waktola, A. 1999: “Exploratory Study of Two Regions in Ethiopia: Identification of Target Areas and partners for Intervention”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 7. Mossige, A. 2000: “Workshop on Gender and Rural Development – Training Manual”, Drylands Coordination Group and Noragric, Agricultural University of Norway.


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8. Synnevåg, G. et Halassy, S. 2000: ”Sécurité Sémenciére: Etude de la gestion et de l’approvisionnement en semences dans deux villages du cercle de Ké-Macina au Mali: Kélle et Tangana”, Groupe de Coordination des Zones Arides et Noragric, Agricultural University of Norway. 9. Abesha, D., Waktola, A, Aune, J.B. 2000: ”Agricutural Extension in the Drylands of Ethiopia”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 10. Sydness, M., Doumbia, S. et Diakité K. 2000: ”Atelier sur la désentralisation au Mali”, Groupe de Coordination des Zones Arides et Noragric, Agricultural University of Norway. 11. N’Dior, P. A. et Traore, N. 2000: ”Etude sur les programmes d’espargne et de credit au Mali”, Groupe de Coordination des Zones Arides et Noragric, Agricultural University of Norway. 12. Lode, K. and G. Kassa. 2001: ”Proceedings from a Workshop on Conflict Resolution Organised by the Drylands Coordination Group (DCG), November 8-10, 2000 Nazareth, Ethiopia”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 13. Shiferaw, B. and A. Wolday, 2001: “Revisiting the Regulatory and Supervision Framework of the Micro-Finance Industry in Ethiopia”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 14 A. Doumbia, M. D., A. Berthé and J. B. Aune, 2001: “Intergrated Plant Nutrition Management (IPNM): Practical Testing of Technologies with Farmers Groups”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 14 B. Doumbia, M. D., A. Berthé and J. B. Aune, 2001: “Gestion Intégrée de Nutriments Bégetaux (GINV): Tests Pratiques de Technologies avec des Groupes de Paysans”, Groupe de Coordination des Zones Arides et Noragric, Agricultural University of Norway. 15. Larsen, K. and M. Hassan, 2001: “Perceptions of Knowledge and Coping Strategies in Nomadic Communities – The case of the Hawawir in Northern Sudan”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 16 A. Mossige, A., Berkele, Y. & Maiga, S., 2001: “Participation of Civil Society in the national Action Programs of the United Nation’s Convention to Combat Desertification: Synthesis of an Assessment in Ethiopia and Mali”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 16 B. Mossige, A., Berkele, Y. & Maiga, S., 2001: “La Participation de la Societe Civile aux Programme d’Actions Nationaux de la Convention des Nations Unies sur la lutte contre la Desertification”, Groupe de Coordination des Zones Arides et Noragric, Agricultural University of Norway. 17. Kebebew, F., D. Tsegaye and G. Synnevåg: “Traditional Coping Strategies of the Afar and Borana Pastoralists in Response to Drought”, Drylands Coordination Group and Noragric, Agricultural University of Norway. 18. Shanmugaratnam, N., D. Mamer and M. R. Kenyi, 2002: “From Emergency Relief to Local Development and Civil Society Building: Experiences from the Norwegian Peoples’ Aid’s Interventions in Southern Sudan”, Drylands Coordination Group and Noragric, Agricultural University of Norway.


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19. Mitiku, H. and S. N. Merga, 2002: Workshop on the Experience of Water Harvesting in the Drylands of Ethiopia: Principles and practices”, Drylands Coordination Group and Noragric, Agricultural University of Norway.


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Drylands Coordination Group Addresses in Norway: ADRA Norge, P.O. Box 6897 St. Olavs Plass, 0165 Oslo, Norway Tel: +47 22 11 20 80, Fax: +47 22 20 53 27 e-mail: [email protected] CARE Norge, Universitetsgt. 12, 0164 Oslo, Norway Tel: +47 22 20 39 30, Fax: +47 22 20 39 36 e-mail: [email protected] The Development Fund, Nedregt. 8, 0551 Oslo, Norway Tel: +47 22 35 10 10, Fax: .+47 22 35 20 60 e-mail: [email protected] Norwegian Church Aid, P.O. Box 4544 Torshov, 0404 Oslo, Norway Tel: +47 22 09 27 99, Fax: + 47 22 09 27 20 e-mail: [email protected] Norwegian People’s Aid, P.O. Box 8844 Youngstorget, 0028 Oslo, Norway Tel: + 47 22 03 77 00, Fax: + 47 22 20 08 70 e-mail: [email protected] Strømme Foundation, P.O. Box 414, 4601 Kristiansand, Norway Tel: +47 38 12 75 00, Fax: + 47 38 02 57 10 e-mail: [email protected] Noragric, Centre for International Environment and Development Studies Agricultural University of Norway, P.O. Box 5001, 1432 Ås, Norway Tel: +47 64 94 99 50, Fax: +47 64 94 07 60 e-mail: [email protected]

management of salt-affected soils in the ncew shemshemia

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