Guide to efficient plant nutrition management

AF O

FI A T PA N

I S

Food andAgr i cu l tureOrganizat ionoftheUni ted Nat ions

challenges

sources of plant nutrients

management ofplant nutrients

environmentalissues

policies

Guide to efficient

plant nutrition management

LAND AND WATER DEVELOPMENT DIVISIONFOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS

Rome, 1998

The designations employed and the presentation of material in thispublication do not imply the expression of any opinion whatsoever on

the part of the Food and Agriculture Organization of the United Nations

All rights reserved. No part of this publication may be reproduced, storedin a retrieval system, or transmitted in any form or by any means,

electronic, mechanical, photocopying or otherwise, without the priorpermission of the copyright holder. Applications for such permission, with

a statement of the purpose and extent of the reproduction, should beaddressed to the Director, Information Division, Food and Agriculture

Organization of the United Nations, Viale delle Terme di Caracalla, 00100 Rome, Italy.

© FAO 1998

Plant nutrients are essential for producing suffi-cient and healthy food for the world’s expand-ing population. Plant nutrients are therefore a

vital component of any system of sustainable agricul-ture. Moreover, agricultural intensification requiresincreased flows of plant nutrients to crops and higheruptake of those nutrients by crops. The depletion ofnutrient stocks in the soil, which is occurring in manydeveloping countries, is a major but often hidden formof land degradation. On the other hand, excessiveapplications of nutrients, or inefficient management,can cause environmental problems, especially if largequantities of nutrients are lost from the soil/crop sys-tem into water or the air.

The Guide to efficient plant nutrition managementaddresses some major issues related to the agronomicmanagement of plant nutrients in an attempt to ensureboth enhanced and sustainable agricultural productionand to safeguard the environment.

This guide is intended to promote the assessment ofplant nutrient requirements on a farming system basisand monitoring of soil fertility. It will help in the for-mulation of advice to governments and eventually leg-islation in the field of fertilizer use and plant nutrition.As the guide emphasizes, plant nutrient managementshould be a major concern at both the farmer and thenational level.

The guide is intended to assist everyone concernedwith the manufacture, marketing and use of fertilizersin working towards efficient and sustainable plantnutrition management. The advice it contains shouldbe promoted by governments in regional groupings, byinternational and national non-governmental organiza-tions, by the fertilizer industry and by United Nationsagencies.

All parties addressed by this guide are invited toobserve and promote its general principles. The co-operation of the fertilizer industry in observing theseprinciples will be particularly valuable.

As a follow-up, soil fertility status and the evolutionof soil fertility should be evaluated and monitored byagro-ecological zone. Particular emphasis should beput on long-term trends in soil fertility so that plantnutrient depletion, wherever observed, can be coun-tered.

Environmental impact assessments should be car-ried out regularly, especially in zones with intensive useof fertilizers.

Robert BrinkmanDirector, Land and Water Development Division

Foreword

This document benefited from

contributions from FAO’s Legal Office.

FAO is grateful to the following

persons and organizations for their

contributions and comments:

R. Dudal (Belgium)

A. Finck (Germany)

C. Hera (FAO/IAEA Joint Division,

Austria)

J. Neeteson (The Netherlands)

C. Pieri (World Bank, United States)

D. Powlson (United Kingdom)

N. E. Nielsen (Denmark)

P. Sequi (Italy)

J. P. Pichot (France)

The International Fertilizer Industry

Association (France)

ACKNOWLEDGEMENTS

iii

iv

Increasing agricultural production by improvingplant nutrition management, together with a betteruse of other production factors, is a complex chal-

lenge. Agricultural intensification requires increasedflows of plant nutrients to crops, a higher nutrientuptake and higher stocks of plant nutrients in soils.This also results in a higher production of cropresidues, manure and organic wastes. Excessive use ofnutrients, inefficient management of cropping systems,and the inefficient use of residues and wastes result inlosses of plant nutrients, which means an economic lossfor the farmer. On the other hand, an inadequate orinsufficient use of plant nutrients creates an insidiousdepletion of the stock of plant nutrients on the farm,which will also mean an economic loss for the farmer.Environmental hazards can be created by applying toomuch nutrient compared with the uptake capacity ofcropping systems, while the depletion of nutrient stocksis a major, but often hidden, form of environmentaldegradation. Plant nutrition management dependslargely on prevailing economic and social conditions.Farmers’ decisions depend on their economic situationand their socio-economic environment, on their per-ception of economic signals and on their acceptance ofrisks.

The fundamental assumption of this guide is thatplant nutrition management can contribute to foodsecurity and to the sustainable production of agricul-tural goods without harm to the environment.

The guide addresses all parties engaged in or influ-encing the production, distribution and use of plantnutrients: local organic products, mineral fertilizersand biological inoculants. It proposes responsibilities,guidelines and a basis for agreement among the partiesconcerned to share the promotion and development ofintensified plant nutrition management guided byaccurate policies through coherent plans for action.

The Guide proposes the adoption of Integrated

Plant Nutrition Systems (IPNS) which enhance soil pro-ductivity through a balanced use of local and externalsources of plant nutrients in a way that maintains orimproves soil fertility and is environmentally-friendly.In the medium term, IPNS help accumulate plantnutrient stocks (in soils and crop residues) as well ascapital for sustainable continuation of the intensifica-tion process.

The guide emphasizes the urgent need to identifyand develop local technologies and decision-makingmechanisms to improve plant nutrition practices.Disseminating information and training small-scalefarmers are important ways of promoting the intensi-fied, sustainable and environmentally- friendly farmingpractices that will increase farmers’ incomes.

The essential components of efficient plant nutri-tion management, which the guide aims at communi-cating, are described below.

● The sources of plant nutrients are described andinformation is provided on their efficient use foragricultural intensification and their potentialimpact on the environment.

● Optimizing the management of plant nutrients, asa part of sound agricultural intensification, resultsfrom a balanced supply of plant nutrient sources,maintaining or increasing the capital of plant nutri-ents on the farm and the efficiency of the nutrientsinvolved in crop production, and maximizingincome for farmers within the local economic con-text.

● Advice on plant nutrition management shouldinclude assistance in decision making at plot and atfarm level, in order to optimize the use of localresources and the ability of farmers to intensify pro-duction within the existing economic environment.

Executive summary

Advice should also be provided at village level or insmall watersheds on the management of and invest-ment in local sources of nutrients available fromvegetation and livestock. Such advice is most cost-effective if the private and public sectors cooperatein helping the farmers. Information about thepotential environmental impact of plant nutrientmanagement should be provided to everyone con-cerned. Correct research backup is essential.

● The possible environmental impact of the overuse,underuse and misuse of plant nutrient sources isdiscussed.

● National policies should facilitate the developmentof sound plant nutrition management and theinvestments needed to intensify production whileconserving the natural resource base.

The major aspects put forward for considerationare:

● assessment of plant nutrient requirements formeeting crop production targets;

● choice of sources and methods of supply;● determination of the level of domestic fertilizer

production required;● price levels and the issue of subsidies for plant

nutrients;● legislative aspects; and● support for extension and research.

Policy-making in these areas determines the extentto which farmers have access to plant nutrients and areable to increase their production while maintaining soilfertility. A farmer needs purchasing power to obtainexternal inputs, as well as advice on how to use them ina balanced way. The guide outlines appropriate policiesin the areas of assessment, marketing, transport andstorage, training, pricing, legislation, packaging, adviceand planning, and financing. It emphasizes that theright balance of government and private participationin the production, importation and distribution of fer-tilizers needs to be found. In addition, it advocates set-ting up national plant nutrition focal points to adviseon policy and to regulate the availability, quality, pro-

duction and trade of plant nutrients (in particular fer-tilizers) in a way that complements the overall plantnutrition strategy of the government, and then toimplement that policy.

vi

Contents

Foreword iii

Executive summary iv

Challenges for plant nutrition management 1

Sources of plant nutrients 3Nature and supply of plant nutrientsGathering sources of plant nutrients

Management of plant nutrients 6Integrated Plant Nutrition SystemsPlant nutrient balanceEconomic aspects of fertilizer useAdvice on efficient plant nutrition Research backup

Environmental issues 14Negative effects with high inputsNegative effects with low inputsOvercoming the negative effects

Policies for effective plant nutrition 17

Bibliography 19

1

The challenges for plant nutrition managementare to maintain (and where possible increase)sustainable crop productivity to meet demands

for food and raw materials, and to enhance the quality ofland and water resources. There is no contradictionbetween these challenges. Indeed, environmental haz-ards can be minimized by matching plant nutrients withcrop requirements, and judicious soil and water conser-vation methods.

Agriculture inevitably removes plant nutrients fromthe soil and from the farm. Consequently, if a farmingsystem is to be sustainable, these nutrients have to bereplaced by whatever sources are available. For thefarmer, nutrient losses are money wasted.

In many developing countries, the loss of soil fertili-ty from continual nutrient mining by crop removalwithout adequate replenishment, combined with imbal-anced plant nutrition practices, poses a serious threat

to agricultural production. It is already causing yielddecreases as large as those caused by other forms ofenvironmental degradation.

While recycling and transfer of nutrients from non-crop areas, crop residues and animal manure can par-tially make up for exports of nutrients by harvestedproducts, the use of external sources such as mineralfertilizers is essential to meet crop requirements and toincrease crop production in many farming systems.Intensification of agriculture by increasing the use ofplant nutrients is limited by environmental hazards andeconomic constraints. In industrialized countries, envi-ronmental issues and international trade agreementsrestricting surplus food production are now the limit-ing factors on further intensification; in developingcountries, the high cost of external sources of nutrientsand their inadequate availability limit intensification.

Considering the importance of plant nutrients to

Challenges for plant nutrition management

The objectives are to set forth

responsibilities and propose guidelines

for all parties engaged in or influencing

the production, distribution and use of

plant nutrients, with special reference

to fertilizers.

Reference is made to the shared

responsibility of many segments of

society, including governments,

individually or in regional groupings,

industry, trade, international

institutions and farmers, to work

together with a common aim: an

efficient use of plant nutrients that will

lead to intensified and sustainable

agriculture and protection of the

natural resource base.

The guide specifically aims to:

● promote a better understanding of

the role of plant nutrients in

securing the sustainability of

agriculture and in building up and

maintaining soil productivity;

● ensure that all sources of plant

nutrients, especially fertilizers, are

used efficiently for increased

agricultural production;

● identify how the application of plant

nutrients can affect the environment

and point to ways of avoiding

negative impacts;

● formulate recommendations for

plant nutrition management in a

framework of IPNS, taking into

account farmers’ production goals

and strategies within specific agro-

ecological, social and economic

conditions;

● promote the development of sound

advisory services and efficient input

supply systems to farmers;

● facilitate the emergence of farmers’

associations leading to the adoption

of sound plant nutrition practices;

and

● provide elements for the design of

national strategies and policies for

effective plant nutrition in support

of agricultural intensification and

rural development.

THE OBJECTIVES OF THIS GUIDE

2

challenges for plant nutrition management

agricultural production, it is imperative to establish therelationships between yield, use of plant nutrients, eco-nomic feasibility and environmental quality. What farm-ers need to know is how much and which plant nutri-ents they should supply to provide the optimum eco-nomic increase in yield without damaging the environ-ment. The answer depends on the ecological, socialand economic characteristics of each farming system.

Increased attention is now being paid to developingIntegrated Plant Nutrition Systems (IPNS) that main-tain or enhance soil productivity through a balanceduse of mineral fertilizers combined with organicsources of plant nutrients, including biological nitro-gen fixation. IPNS is ecologically, socially and econom-ically viable, and it can increase both soil productivityand crop yields. It focuses first on the seasonal or annu-al cropping system, rather than on an individual crop;secondly, on the management of plant nutrients in thewhole farming system; and, thirdly, on the concept ofvillage or community areas rather than individualfields.

The FAO study World agriculture: towards 2010 esti-mates that about two-thirds of the needed increase incrop production in developing countries will have tocome from yield increases on land already under culti-

vation. Plant nutrients are the most important inputsfor increasing yields. Over the past three decades, addi-tional nutrients applied as fertilizer have been respon-sible for 55 percent of the yield increases in developingcountries. The development of plant nutrition man-agement to increase the quantity of plant nutrients infarming systems and thus crop productivity is a majorchallenge for food security and rural development.

This guide promotes the effective management ofplant nutrients. It is relevant to farmers, advisory ser-vices, research and extension bodies, developmentagencies, financial institutions, the fertilizer industryand government decision-makers in both developedand developing countries — in fact to all those con-cerned with sustainable agricultural production andenvironmental protection.

3

Nature and supply of plant nutrients

Plants build up their biomass using water, carbon diox-ide from the air, energy from sunlight and nutrientstaken up from the soil and water. For optimum plantgrowth, nutrients must be available:

● as solutes in the soil water;● in adequate and balanced amounts, corresponding

to the instant demand of the crop;● in a form which is accessible to the root system

(except when provided through foliage).

Plants are supplied with nutrients mainly from:

● soil reserves;● mineral fertilizers;● organic sources;● atmospheric nitrogen through biological fixation;● aerial deposition caused by wind and rain;● irrigation, flood or groundwater, and sedimenta-

tion from runoff.

These sources are used by farmers according totheir availability and affordability. The total amount ofplant nutrients available to the crop is a key factordetermining yield.

Plant nutrients These are elements that are essential for plant growthand that are taken up from the soil or from water —irrigation, flood or groundwater — or are supplied viaa hydroponic medium. The primary nutrients are nitro-gen, phosphorus and potassium which are consumedin relatively large amounts. Three secondary nutrientsare taken up in smaller quantities but are essential forplant growth: calcium, magnesium and sulphur.Micronutrients or trace elements are required in very

small quantities but are often important for plant oranimal metabolism. They include iron, zinc, man-ganese, boron, copper, molybdenum and chlorine. Inaddition, some plants benefit from the presence ofsodium, cobalt and silicon but these do not rank asessential nutrients.

Soil reservesSoils contain natural reserves of plant nutrients inquantities that depend on soil composition and stage ofweathering. These reserves are often in forms unavail-able to plants, and only a minor portion is releasedeach year through biological activity or chemicalprocesses. This release is too slow to compensate for theremoval of nutrients from agricultural production,especially in the humid tropics where soils are stronglyweathered. The quantities (or stock) of plant nutrientsavailable for a crop are determined by the supply ofnutrients to the crop from internal and externalsources, the uptake of nutrients by the crop, and lossesof plant nutrient to the environment. Thus plant nutri-ent stock is constantly changing. The capacity of a soilto store easily-available plant nutrients is an importantfactor in plant nutrition management. Chemical analy-sis can provide an approximation of the nutrient stock,the accuracy of which is related to soil type, croppingconditions and crop species.

Fertilizers These are mineral or organic substances, natural or man-ufactured, that are applied to soil, irrigation water or ahydroponic medium, to supply plants with nutrients.Fertilizers contain at least 5 percent of one or more of thethree primary nutrients (N, P2O5, K2O). The term isoften used as an abbreviation for mineral fertilizers (seebelow). Products with less than 5 percent of combinedplant nutrients are called plant nutrient sources. Thelegal definition of a fertilizer varies in different countries.

Sources of plant nutrients

4

sources of plant nutrients

Mineral fertilizers Mineral fertilizers are manufactured in liquid or solidform, usually in an industrial process. They can supplymain nutrients, secondary nutrients, micronutrients ormixtures of nutrients. Straight fertilizers supply onlyone nutrient while complex fertilizers supply several.Compound fertilizers are produced by the blending orchemical linkage of straight fertilizers or nutrients. Theterms chemical or artificial fertilizers are often used forthese products but are misleading because the nutri-ents supplied by mineral fertilizers are the same asthose supplied by the mineralization of organic materi-al through soil micro-organisms; indeed, some fertiliz-ers are directly derived from natural products such asguano, potassium salts or natural sodium nitrates.Mineral fertilizers have a higher plant nutrient contentand a lower bulk than organic sources of plant nutri-ents. High-grade fertilizers contain more plant nutri-ents (up to 82 percent) than low-grade fertilizers, pro-ducing savings on transport and handling costs.

Organic sourcesThese nutrients are materials of organic origin, eithernatural or processed. The term organic fertilizers isoften used incorrectly to describe nutrient sources con-taining less than 5 percent of at least one of the threeprimary nutrients. In this sense, some organic materialsof animal origin — such as guano, bone meal, fish-meal, and blood — are true fertilizers but commonlyused organic sources of nutrients, such as manure, slur-ry, compost and sewage sludge, are not. Organic mate-rials can be used to increase the amount of organic mat-ter in the soil, thus enhancing its water retention andexchange capacity, and its physical condition.

Farmyard or animal manure is a mixture of animalexcreta and the litter used for bedding. Green manureis fresh, locally produced plant material that is workedinto the soil without composting or digestion by ani-mals. When leguminous crops are used as greenmanure, the atmospheric nitrogen they have fixed isalso added to the soil. Slurry is a mixture of liquid andsolid animal excreta, sometimes diluted with water.Sludge is residual organic material derived from sewage.Compost consists of organic materials of animal andplant origin partially decomposed through fermenta-tion; mineral fertilizers are sometimes added to it.

Biological nitrogen fixationSome micro-organisms are able to convert nitrogen inthe air to ammonia for use as their nitrogen source.The conversion is made by bacteria living either ontheir own in the soil or, on a considerably larger scale,in symbiosis with leguminous plants or trees (rhizobi-um), or other specific trees (actinomycetes), or with azol-la in aquatic conditions (blue-green algae). Biologicalnitrogen fixation can be enhanced by inoculation withefficient strains of nitrogen-fixing micro-organisms,part of the fixed nitrogen being directly assimilated byplants. The term biofertilizers is sometimes inappropri-ately used for these micro-organisms; microbial inocu-lants is the preferred term.

Aerial depositionSome nutrients are supplied in small quantities to thesoil surface through aerial deposition. These includenitrates in rainwater, ammonia as a gas or dissolved inrainwater, sulphur in acid rain, salts and chlorine inmarine spray and calcium in the form of dust.

Irrigation water, floodwater and groundwaterThese sources also supply plant nutrients, either natu-rally or because fertilizers have been added to the irri-gation water. While water often contains small amountsof nutrients, irrigation can also result in a loss of nutri-ents from leaching. Some of the nutrients provided bysurface and groundwater originate from plant nutrientlosses within the watershed.

Soil amendmentsAmendments are substances that are applied to the soilto correct a major constraint other than low nutrientcontent. Lime, for example, is used to remedy acidity;phosphates are used to reduce phosphorus fixation;gypsum is used to improve sodic (alkali) soils; and peatcan be added to the surface layers to increase organicmatter content.

Gathering sources of plant nutrients

The natural plant nutrients found in the soil aredeposited there either from the air or from water, orresult from nitrogen fixation and the weathering of

5

mineral particles in the soil. Vegetation takes up someof these nutrients, some are geographically redistributedby runoff, and some are lost by volatilization, fixationand leaching. Farmers harvest the natural supply ofthese nutrients for their crops and reorganize their dis-tribution in space and time through their productionsystems.

On land under natural vegetation, the organic mat-ter that accumulates at the soil surface releases plantnutrients as it decomposes (or when it is burnt in afire). Nutrients taken up from deeper layers thus even-tually become available to plants in the topsoil. Slash-and-burn systems exploit this nutrient managementtechnique. As crops are harvested, the local supply ofnutrients is progressively depleted; eventually the landmust be left in a prolonged fallow or replenished withexternal nutrients.

The practice of allowing short fallow periods onarable land is another means of accumulating the nat-ural supply of nutrients for a later cropping period.However, much less nutrients are gathered in a shortfallow period than in a long fallow, of ten years or more,in perennial vegetation.

Farming systems redistribute and concentrate nat-ural nutrients in a number of ways. For example:

● some traditional farming systems allow livestock tograze a large non-cropped area and the manure is

then collected and spread over a selected croppedarea;

● forest litter is collected and used to mulch acropped area;

● manure from animals kept in corrals and shelters isspread on cropped areas;

● feedstuffs are imported to the farm and fed to live-stock whose manure is then spread over croppedareas;

● crop residues are collected and processed (by com-posting or in biogas plants) and then spread oncropped areas; and

● leguminous crops are grown to supply the plantnutrients that are produced by nitrogen fixation.

6

Restoring, maintaining and increasing soil fertil-ity are major agricultural priorities, particular-ly in the many parts of the developing world

where soils are inherently poor in plant nutrients, andthe demand for food and raw materials is increasingrapidly. In these areas, there is a need to intensify cropproduction to meet demand for food without using for-mer land fallow practices. A fertile soil provides a soundbasis for flexible food production systems that, withinthe constraints of soil and climate, can grow a widerange of crops to meet changing needs.

Integrated Plant Nutrition Systems

IPNS associate available, accessible and affordableplant nutrients to increase farm productivity and eco-nomic returns.

IPNS operate at plot, farm and village or territorylevels. At the plot level, they are designed to optimizethe uptake of plant nutrients by the crop and increasethe productivity of that uptake (the ratio between har-

vested products and nutrient uptake) while reducingnutrient losses. The optimal nutrient supply is deter-mined by the production methods used, the prevailingprices of fertilizers, the cost of mobilizing local nutrientsources and the commercial value of the crop. IPNSincreases plant nutrient stocks in soils and improvesother aspects of soil fertility such as water infiltrationand water-holding capacity; it also reduces limitationson crop growth caused by factors such as soil acidityand compaction. IPNS make use of crop rotations tooptimize nitrogen fixation, the efficient managementof crop residues, exploration of the soil by developingrooting systems, and management methods that limitnutrient losses (by exploiting nutrients that arereleased slowly from organic and mineral sources).

At farm level, IPNS aim to optimize the productivityof the flows of nutrients passing through the farmingsystem during a crop rotation (see figure on page 11).IPNS improve the production capacity of farmersthrough application of external plant nutrient sourcesand amendments, efficient processing, and recycling ofcrop residues and on-farm organic wastes that limitplant nutrient losses. IPNS empower farmers by increas-ing their technical know-how and decision-makingcapacity, and promote changes in land use, crop rota-tions, and interactions among forestry, livestock andcropping systems in support of agricultural intensifica-tion. IPNS require financial and labour investments,generate additional income and promote an increasedrate of return from all inputs. IPNS involve risk man-agement and enhance the synergy among crop, waterand plant nutrition management.

At the level of the village or farming community,IPNS take into account plant nutrient sources outsidethe cropped areas. These include plant nutrients in irri-gation water and flood sediments, manure produced bylivestock grazing, forests and permanent pastures, andforest litter and organic material that is physically trans-ferred from forest and pastures to the cropped area. In

Management of plant nutrients

IPNS is used to maintain or adjust soil fertility and plant

nutrient supply to achieve a given level of crop

production. This is done by optimizing the benefits from

all possible sources of plant nutrients.

The main objectives are to:

● maintain or enhance soil productivity through a

balanced use of mineral fertilizers combined with

organic and biological sources of plant nutrients;

● improve the stock of plant nutrients in the soil;

● improve the efficiency of plant nutrients, thus limiting

losses to the environment.

FAO’S IPNS APPROACH

peri-urban agriculture, farmers purchase manure fromindustrial livestock systems and organic wastes fromcities. IPNS promote the rationalization of the transferof organic matter and plant nutrients from non-cropped areas to cropped areas, and the mobilizationof unused nutrient resources or the saving of valuablenutrient sources diverted as domestic fuel, raw materi-

als for building or for industrial purposes. At villagelevel, IPNS also involve the development of the finan-cial capacity of farmers for the adoption of changethrough farmers’ associations.

Plant nutrient balance

An agricultural ecosystem differs from a natural one inthat plant nutrients are constantly being removed andexported, and in that sources of plant nutrients outsidethe cropped area may be used to increase production.In a natural ecosystem, the supply of nutrients at leastcompensates losses from runoff, leaching and volatiliza-tion and, in favourable conditions, nutrients accumu-

7

PLANT NUTRIENT BALANCE SHEET

CROPPING SYSTEM CONSUMPTION

SYSTEM

ENVIRONMENT

LOSSES OF

NUTRIENTS

leaching, runoff

and volatilization

available plant nutrients

EXTERNAL INPUTS OF NUTRIENTS

fertilizers and amendments

EXPORTS OF NUTRIENTS

SUPPLY

IMMOBILIZEDCAPITAL:

soil reserve

WORKINGCAPITAL:

rain, irrigationwater, greenmanure, N-fixation,manure, cropresidues

CROPS PRODUCTS RESIDUES

HUMANS

LIVESTOCK

C

B

A

C

WASTES

UPTAKE

▼ The following plant nutrient balance sheet highlightsthree ways in which farmers can improve nutrient use:A: reduction of plant nutrient losses by limiting runoffthrough investment in soil drainage;B: increase of nitrogen uptake by introducing cover crops;C: reduction of nitrogen losses from wastes by improvingmanure management.

late in the perennial vegetation and in the topsoil. Inagricultural systems, farmers intervene at several stagesof the plant nutrient cycle in order to optimize cropproduction and the corresponding export of nutrients(see diagram opposite).

Farmers try to satisfy plant nutrient demand byusing the ‘immobilized capital’ of plant nutrients in thesoil and the ‘working capital’ of plant nutrients fromnatural and organic sources. They complement thesewith external nutrients. However, the nutrients storedin the soil should not be depleted beyond a criticallevel. These nutrients cannot be transferred rapidlyfrom one plot to another. Plant nutrients in cropresidues, manure, litter from forests, green manure anddomestic wastes compose a ‘working capital’ becausefarmers can transfer them and allocate them to a par-ticular crop in a crop rotation and to a particular plot.

A balance sheet can be established for every nutri-ent. The efficiency of a production system depends onthe importance of crop uptake versus the total supply ofnutrients. High losses of nutrients limit the efficiency.Plant nutrient stocks can be ‘mined’ providing thisdoes not affect the annual supply of nutrients or thegeneral status of soil fertility.

Normally, insufficiency of one plant nutrient limitsthe efficiency with which other plant nutrients aretaken up, reducing crop yield (see diagram below).Unbalanced availability of nutrients can lead to miningof soil reserves for nutrients in short supply and to loss-

es of plant nutrients supplied in excess. Lack of balancealso encourages excessive uptake of the nutrients sup-plied in excess, decreasing the productivity of thosenutrients. Unbalanced fertilization is an uneconomicwaste of scarce resources.

In practice, the quantity of nutrients available forrecycling via plant and animal residues is rarely suffi-cient to compensate for the amounts removed in agri-cultural products, even in low-productivity situations. Inaddition, losses inevitably occur, even in the best-man-aged systems. Consequently, mineral fertilizers have toplay a key role in areas where increased agriculturalproduction is required.

Economic aspects of fertilizer use

Farmers apply plant nutrients only if their effects oncrop yields are profitable. The decision to apply exter-nal plant nutrients is generally based on economics(price and affordability) but is also conditioned byavailability and the production risks involved. The pur-suit of higher production has to be balanced against

8

management of plant nutrients

▼ Yield response to balanced plant nutrition: insufficiencyof one plant nutrient limits the efficiency with which otherplant nutrients are taken up, reducing crop yield.

yie

ld

nitrogen level

effect of P

effect of K

price relationshipbetween crop

and plantnutrients

farmer incomecredit

availability

crop market outlooks

availability of localnutrient sources

local conditions, land tenure, climatic conditions, risks and opportunities

AFFORDABILITYOF INITIALPURCHASE

PROFITABILITYOF FERTILIZER

USE

DECISION TOUSE EXTERNAL

PLANTNUTRIENTS

▲ Decision-making process used by farmers for cropfertilization.

the need to maintain soil fertility and avoid soil degra-dation. The profitability of adopting IPNS should, how-ever, be viewed over the long term, since improved effi-ciency in crop nutrient use tends to become apparentonly after several seasons.

A number of economic and institutional factorsmust also be taken into account:

● the price relationship between plant nutrients andthe crops to which they are applied, together withthe market outlook for these crops, determineshow profitable it will be to use fertilizer;

● income and the availability of credit decidewhether farmers can afford to buy plant nutrients;

● lack of security of land tenure can reduce theincentive for farmers to use fertilizers.

Small-scale farmers with few resources are com-pelled to look for short-term results when applyingplant nutrients. The removal of access constraints tomarkets and production technology, and protectionfrom risks, would allow farmers to use plant nutrientseconomically and in ways that support sustainable cropproduction.

Advice on efficient plant nutrition

Providing good advice to farmers and enhancing theirdecision-making capacity is the best way to promote thesustainable intensification of agriculture. Such advice:

● requires a good knowledge of farmers’ croppingsystems, socio-economic conditions and decision-making processes;

● should use farmers' participation to identify andtest suitable innovations;

● should be organized in steps from plot level tofarm, village territory and small watershed level;

● should include short-term suggestions for the fer-tilization of crop rotations and longer-term sugges-tions for accumulating plant nutrients on the farmand improving soil fertility;

● must promote sustainability.

The organization of correct advice is costly and thesharing of this cost among the government, the farmers'

IPNS IMPLEMENTATION METHODOLOGY

9

select target areas

Rapid Rural Appraisal of communities

categorize main production systems and identify limiting factors

select representative locations

hold participatory dialogue with farmersfor site-specific trials (plot level)

experimen-tation

agro-economic evaluation

validation trials

IPNS programme (farm level)

extension of the technologies throughfarmers’ groups (village level)

plant nutrientbalancesheet

chooseexperimental

sites�

choosetreatments

chooseexperimental

design�

evaluation of farmer responsefarm-levelanalysis

10

management of plant nutrients

communities and the private sector is desirable. Thesteps involved are summarized in the diagram IPNSImplementation Methodology.

The extent of the study can be defined only after ini-tial discussions with farmers, extension agents andresearch workers in the area, and a rapid survey of thearea. The latter should be conducted by a multi-disciplinary team including plant and livestock scien-tists, social scientists and economists. The study shoulddetermine the physical, biological and socio-economicenvironments, sociocultural characteristics, and pro-duction system and land use. Discussions should also beheld with farmers to determine their production objec-tives and constraints, and to get a general idea of theirperceptions and living conditions.

Plot level

Advice at plot level should be based on local on-farmexperiments. These experiments will provide informa-tion on the impact of combined nutrient doses, timingof nutrient supply, and sources of nutrients on cropyields. The experiments should be simple and are oftwo types: site-specific trials and validation trials.

The data collected from the trials are used to derivenutrient response curves for the predominant crop-ping systems and conditions. These trials are usuallymanaged by public sector researchers because theyrequire a fair degree of control of variability as well as ahigh level of supervision. Farmer participation in infor-mation gathering and decision making is minimal.

However, researchers can interact with the farmers andlearn about their methods of production. Importantconsiderations in planning site-specific trials are popu-lation definition, choice of sites, choice of treatments,experimental designs, and management of the experi-ment.

Sites for the trials should be representative of thefarming conditions of the area being studied.

Site-specific, researcher-managed trialsFarmers must be involved in all stages of planning andexecution of the trials so that they understand the aimsand objectives of the experiment and are willing to par-ticipate. Researchers and extension workers must firstlisten to the farmers’ concerns and establish a relation-ship with the farmer. Farmers must feel that they areequal partners in the experimentation process. Thebenefits of the research, the importance of farmer par-ticipation and the expectations of the relationship mustbe explained to farmers. Each participant —researcher, extension worker and farmer — must beapprised of his or her responsibilities (who does what,who takes what risks and who gets what products) sothat all operations are conducted on time and there isno misunderstanding of roles.

All data collected from the trials should bescreened, validated, analysed and interpreted by theresearchers after completion of the trial. The resultsobtained will be used to adjust treatments for subse-quent trials and to identify promising treatments whichcan be applied in validation trials.

▲ Discussions between a multidisciplinary team and farmers.

▲ On-farm experimental site.

Validation trialsWhen promising plant nutrition treatments have beenidentified, they are tested on farmers’ fields in validationtrials. Validation trials are conducted by farmers them-selves under the overall supervision of extension workersand researchers. These trials generate valuable informa-tion on farmers’ understanding, acceptance, rejection,adaptation or adoption of the proposed innovations.

The farms should be selected for characteristics (suchas slope, integration of livestock and level of manage-ment) that are similar to those used for the site-specifictrials. The farms should also be representative of all farm-ers in the area of study — both good and bad, so that therange of possible responses to the technology is obtained.

Data generated from these validation trials arescreened, validated, analysed and interpreted by exten-sion workers. The data are then compared with the ref-erences obtained from the researcher-managed trials toevaluate the farmers’ progress and determine possibleimprovements.

Farm level

Farmers’ decisions on how to use plant nutrientsdepend on the situation of the entire farm and its croprotation system. Factors taken into consideration

include: production objectives, available resources(both fixed and variable, such as land, labour, capitaland credit), needs for home consumption, marketopportunities and climatic conditions.

These factors must be well understood before alter-native plant nutrition schemes can be suggested. Inaddition, advisers must identify the centres of decisionmaking, the organization of land use and crop rota-tions, and the competing demands for scarce resourcessuch as organic material, labour and capital.

As a first step, an apparent plant nutrient balance(inputs versus outputs) as well as the practices whichmay be contributing to nutrient losses or inefficientplant nutrient management should be analysed. Thisanalysis may suggest alternative technologies. The boxbelow gives some potential solutions.

Once all potential plant nutrient sources have beenidentified and possible technologies selected, farmerscan determine the correct mix of these technologies tooptimize their resource use and meet their productionobjectives. The new alternatives may involve an increasein labour requirements or financial investments, modi-fication of the farm structure or adaptation of land useand crop rotations. Arrangements will, therefore, needto be made for a complementary supply of externalinputs. In particular, attention should be given to farm-

11

source of nutrient loss technology option

Leaching, volatilization or Cover crops to trap most of remaining nutrients

immobilization after harvest Production of very short-term crops with limited instant demand for nutrients

after the main crop has matured

Fires, leaching and runoff of Modification of methods of land preparation, livestock feeding, crop rotation or

crop residues and composts land use

Livestock waste products Urine and dung collected, processed and re-applied to cropped area

Better management of manure and slurries by modifying livestock housing and

organizing cheap, labour-saving collection systems for wastes (these systems

should be socially and culturally acceptable to the farmer)

Domestic and human Recycle wastes by organizing cheap, effective, labour-saving collection and

waste products processing systems. These systems should be safe, and socially and culturally

acceptable

Ferment wastes in tanks at high temperatures and mix wastes with crop residues

MANAGEMENT SOLUTIONS TO PLANT NUTRIENT LOSSES

ers’ purchasing capacity for these external inputs. Theproposed technological package which entails the useof plant nutrients from different sources must be testedto verify its appropriateness to the farmers’ situationand to evaluate farmers’ acceptance of the technology.This is done through a network of local pilot farmswhich is used to evaluate the impact of change on farm-ing conditions. The farms also serve as ‘demonstrationplots’ for neighbouring farmers who may adopt thetechnology if they see it is to their benefit.

In implementing the technology on the pilot farms,farmers must agree on:

● their need to change from their current produc-tion system;

● the way in which they and the extension workerswill implement the change; and

● mechanisms of risk management during thechange.

For these reasons, the choice of farmers and the rela-tionship between farmer and adviser are critical to suc-cess. Farmers should be representative of the regionand willing to cooperate. Close interaction betweenextension workers and farmers is needed at all times sothat farmers’ questions can be answered. This alsoallows the extension worker to evaluate the farmers’response to the technology and find out why theyaccept or reject it. Sometimes, farmers modify the pro-posed technology. Extension workers can then deter-mine the reasons for the change and alter treatments insubsequent seasons.

The network of pilot farms should run for at leastone entire crop rotation, with the results for each sea-son being used to adjust treatments for subsequentcrops. Estimates should be made of crop productionand productivity, as well as plant nutrient status, andeconomic variables such as cash flows, savings andlabour inputs. The decision to change the mix of nutri-ent sources should be guided by whether the benefits ofthe innovation (both economic and social) outweighthe cost of the investment.

The process of planning, implementing and evalu-ating change at the farm level is costly and requires acadre of trained researchers and extension workers,and costly equipment. It can therefore be done onlythrough a limited series of case studies. These can thenbe used to generate guidelines, methods and referencematerial which can be adapted by other researchersand extension workers for their specific situations.

Village level

In many traditional low input/low output farming sys-tems, plant nutrition management relies on local nutri-ent resources collected in areas other than thosefarmed. Development of an efficient plant nutritionmanagement system should, therefore, extend beyondthe farm to the village territory. The main considera-tions at the village level are:

● management of the transfer of plant nutrients fromnon-cropped to cropped areas;

● investments for soil and water conservation andtheir impact on plant nutrient efficiency;

● the effect of poor plant nutrition managementpractices on the village community; and

● farmers’ groups and organizations.

Plant nutrients from non-cropped areas include lit-ter from forests and fodder from pastures. Improvingthe transfer of these materials to the cropped area canenhance the plant nutrient content in the croppedarea.

Some examples of improved management practicesinclude the cultivation of leguminous forest species,alley cropping of forests with pasture crops, mineral fer-tilization of pastures, regulation of bush fires and devel-

12

management of plant nutrients

▲ Green manuring of leguminous plants on a pilot farm.

opment of systems for allocating manure produced bycollective herds.

Soil and water conservation can greatly reduce loss-es of plant nutrients through runoff and leaching. Inaddition, water harvesting techniques and the develop-ment of irrigation will lead to increased efficiency ofnutrient use. These investments require the coopera-tion of the entire village and must therefore be consid-ered while developing efficient plant nutrition man-agement systems.

Poor plant nutrient management by individualfarmers results in a decrease in soil fertility because ofheavy mining, erosion, silting and deforestation.Similarly, an oversupply of nutrients may pollute drink-ing water and poor management of organic wastes is apotential heath hazard. Thus the involvement of soundplant nutrient management by the entire farming com-munity is essential in developing a system at the villagelevel.

At the village level, farmers’ groups can createfavourable conditions for the procurement of inputsand access to credit. Farmers’ associations, trade con-nections between these associations and the input sec-tor as well as traders in agricultural products and banksshould therefore be encouraged to support improvedplant nutrition management by farmers.

Research backup

Advice on quantities of nutrients to be applied may bebased on empirical results from field experiments, onsoil or plant analysis, on a nutrient balance-sheetapproach, on mathematical models of nutrient dynam-ics, or on a combination of methods. In the absence ofmore detailed information, knowledge of the quantitiesof nutrients removed by crops at the desired yield levelprovides a starting point for estimating nutrientrequirements.

Field experiments are valuable in providing quanti-tative information on the supply of nutrients from soiland organic residues, and the short-term effects oncrop yield from mineral fertilizers supplied in differentforms and quantities. This provides a vital basis foradvising farmers and for testing and improving advicesystems.

Wherever possible, long-term field experiments

should be set up so that residual effects of fertilizersand organic sources on crop growth and soil propertiescan be studied and taken into account when formulat-ing nutrient recommendations. Such experiments canalso provide information on interactions between nutri-ent applications and other agricultural activities, andon the likelihood of unforeseen problems such as envi-ronmental contamination or deficiency of a secondaryor micronutrient. In this context, the need for bal-anced plant nutrition should be emphasized.

Research organizations are responsible for inform-ing the public about the innovations and their potentialimpact.

13

14

Many people are concerned about the possi-ble side effects of plant nutrients on theenvironment. This concern refers both to

the use of mineral fertilizers and organic sources ofnutrients, the latter in connection with intensive live-stock farming that leads to the production of so muchorganic waste that it cannot be used effectively, con-verted or disposed of. Four important issues have to behighlighted:

● Fertilizers are often referred to as agrochemicals, aterm which groups plant nutrients with insecti-cides, herbicides and fungicides. A clear distinctionmust be made between fertilizers, which providenutrients that are essential for plant growth, andbiocides, compounds that kill, which are used forplant protection.

● The environmental effects of applying plant nutri-ents can be positive or negative, and statements onthe issue should be objectively balanced.

● The amounts of plant nutrients, both mineral andorganic, that are applied in developing countriesare relatively low. Local excesses in some industrial

countries should not prejudice increased agricul-tural production in the developing world.

● Environmental problems related to the applicationof plant nutrients depend less on the nature of thenutrients than on the amounts and the way they areapplied. Detrimental effects are mostly due to over-doses or to improper or unbalanced use that can becorrected by improved management practices.

The positive effects are summarized in the boxbelow and the negative effects in the text that follows.

Negative effects with high inputs

Not all nutrients applied to the soil are taken up by thegrowing crop and the remainder may become an envi-ronmental hazard. Unused nutrients can remain in thesoil, be removed in water leaching through the soil orin runoff, or be lost to the atmosphere by volatilization.The relative importance of these phenomena dependson the physico-chemical and biological reactions inwhich the nutrients take part.

Environmental issues

● efficient use of plant nutrients

ensures that yields are higher than

those obtained on the basis of

inherent soil fertility by correcting

either an overall deficiency or an

imbalance of nutrients;

● nutrients removed from the soil

through harvesting and export of

produce can be replenished in order

to maintain and enhance production

potential;

● by increasing yields per unit area on

good arable land, plant nutrients

allow land of low quality, for

example land susceptible to

erosion, to be withdrawn from

cultivation and reduce overall

pressure on the land, including

deforestation and overgrazing of

non-cropped areas;

● plant nutrients ease the problem of

erosion control on cropped areas

because of the protection provided

by a dense and vigorous crop cover;

● IPNS promote the correct

management of plant nutrients on

the farm and the watershed,

optimizing the economic value of

the nutrients and limiting nutrient

losses to the environment.

POSITIVE ENVIRONMENTAL EFFECTS OF PLANT NUTRIENTS

15

Nitrogen: under normal farming conditions, on well-drained soils and with favourable temperature condi-tions, all soluble nitrogen compounds are fairly rapidlyoxidized to nitrate. Nitrate is not absorbed to anyappreciable extent by soil particles. Nitrogen is there-fore the most likely fertilizer element to be leached outinto surface water or groundwater, or to be lost to theatmosphere by denitrification, partly as nitrogen gasand partly as nitrous oxide, which is a greenhouse gas.

Nitrate derived from the breakdown of organic mat-ter in soil, slurry or manure applied to land is also sub-ject to leaching. In many temperate regions, this isoften a more significant source of nitrate than mineralfertilizer. Improved farming practices can help reducethe leaching by maximizing utilization of the nitrateprovided by the soil, and applying just the right amountof nitrogen at the right time for each crop. Researcherstrying to understand changes in nitrate concentrationsin drainage waters should take due account of changesin land use and agricultural practice, as well as fertiliz-er use.

In industrialized farming systems, intensive animal

husbandry is a major cause of the leaching of nitrogen.This is partly due to untimely mineralization of nitro-gen from urine, faeces, and manure or slurry. Nitrateproduced when crop growth is not vigorous can be theorigin of leaching or denitrification. The other mainproblem is ammonia volatilization, both from manureheaps and from soil soon after manure application.Ammonia can also be volatilized if urea fertilizer isapplied to soil of high pH under warm and dry condi-tions.

Phosphorus: plants are supplied with phosphorus inthe form of phosphate ions. They are immobilized inthe soil, being strongly adsorbed by the surfaces of iron,aluminium and manganese oxides and hydroxides, andby clay particles. Applied phosphate that is not taken upby the crop remains in the soil unless it is washed offthe land by runoff or by soil erosion. Phosphate canalso occur in high concentrations in irrigation waterand drainage water from inundated soils. Excess inputsof phosphates to surface waters can lead to eutrophica-tion and algal blooms.

Plant nutrients are supplied from sources such as mineral

fertilizer, the soil, rainfall and dust, irrigation water and

biofixation. As the graph shows. the contributions of these

sources are cumulative.

The crop takes up a portion of the available nitrogen,

regardless of its origin. Available nitrogen not taken up by

the plant is lost to the environment. This loss is the

difference between the total available and the total uptake —

the difference between the top line of the biofixation block

and the relevant uptake curve.

At low levels of supplied N, there is little uptake and so the

loss of N to the environment is high. As the nitrogen supply

increases, the plant takes up more of the nitrogen until it

cannot increase its uptake any further. Supplying additional

nitrogen results in increased losses to the environment.

Plant nutrient loss is minimized at the point where the

distance between the uppermost line and the uptake curve

is smallest. For a crop with a low level of uptake, the

minimum loss of nitrogen is the difference (a-c). For a

higher level of uptake, the minimum loss is (a-b). These

minima occur at the ecological optimum level of N supply.

To increase nutrient efficiency (uptake), farmers should

practise IPNS and optimize all other production factors.

IPNS INCREASES NUTRIENT EFFICIENCY AND REDUCES LOSS TO THE ENVIRONMENT

avai

labl

e ni

troge

n

soil and organic matter

rainfall and dust

irrigation

biofixation

c

b

a

optimum nitrogen efficiency

high N uptake and high yield

low N uptake and low yield

mineral fertilizer

nitrogen supplied

16

environmental issues

Phosphate fertilizers may contain cadmium whensedimentary rock phosphate is used as raw material.Cadmium is also added to the soil by aerial deposition.Current fertilizer usage presents no immediate hazard.However, cadmium should be removed when raw mate-rials are processed, wherever possible.

Potassium: potassium ions, in addition to being takenup by plants, are adsorbed by the soil and can even befixed within clay particles. Added potassium that is nottaken up by the crop is therefore not very mobile insoils that contain clay. In sandy soils, some appliedpotassium may be leached out. Major losses of potassi-um are caused when the element is washed away in liq-uid manure from farmyards and dairies. Potassium inwater has no detrimental effects but may indicate thepresence of sewage or animal effluent. Potassium is nota major factor in the eutrophication of surface waters.

Negative effects with low inputs

Soil fertility: the constant removal of produce withoutor with insufficient replenishment of plant nutrientscauses a steady decline of soil fertility. This mining ofplant nutrients, leading to severe depletion of soil fer-tility, is a major environmental hazard in a number ofdeveloping countries.

Land expansion: if land and labour are available, lowyields resulting from nutrient depletion force farmersto expand cultivated land, often at the expense offorested areas or marginal soils subject to erosion ordesertification.

Amendments: large areas in the tropics are inherentlypoor in soil nutrients and suffer from acidity and alu-minium toxicity. Organic recycling does not offer asolution since the biomass produced in such soils isitself extremely poor in essential plant nutrients. Thesesoils cannot be made productive without amendmentsand a basic input of plant nutrients. Low or zero use ofplant nutrients on such soils prevents the developmentof agricultural production on a sustained basis.

Overcoming the negative effects

The negative effects of applications of plant nutrients,both at low and high levels of input, can be avoided orremedied by good management. Balanced fertilizationshould overcome the hazards of nutrient depletion andof mining soil fertility. Judicious management of plantnutrients can prevent pollution, mainly through prac-tices that reduce losses of nutrients to aquifers or theatmosphere. These practices include balanced, timely,targeted fertilization combined with other practices(such as improved varieties, water management andplant protection) that stimulate maximum uptake ofplant nutrients by the crop. Due attention should alsobe given to controlling losses from soil erosion andrunoff, and through appropriate land management.IPNS provide excellent means of doing this at all pro-ductivity levels if farmers are properly advised.

17

Long-term planning and monitoring of the useof plant nutrients must reconcile four objec-tives:

● agronomic and economic efficiency to maximizeagricultural output from available nutrients;

● increasing the production capacity of the naturalresource base;

● consistency with a country’s overall economic andenvironmental goals;

● safeguarding social security and equity for ruralpopulations.

Assessment: efficient assessment of plant nutrientrequirements is the basis for planning and for decidingon levels of domestic production and imports of fertil-izer products and raw materials, including the use offoreign exchange to finance imports. Fertilizer demandprojection is simply an assessment of the plant nutrient

volumes that will be ordered by farmers and which areneeded to correct any imbalances. Marketing: marketing systems should promote efficientfertilizer use and satisfy farmers' requirements whilehelping meet national food self-reliance goals. Thesesystems require careful design and policies that strikethe right balance between government and private par-ticipation in the production, import and distribution offertilizers. This is a critical issue that is highly depen-dent on national economic and political conditions.

Transport and storage: transport and storage are partof the essential infrastructure needed for the efficientuse of fertilizers. Costs will partly determine the needfor alternative means of transport, and the location andsize of storage facilities.

Training: demonstrations, training and extension onefficient crop-production and fertilizer-use techniquesare essential components of farm-support policies.Extension requirements must be assessed and servicesestablished to address the technological level and expe-rience of the farming community. Adequate technolog-ical packages, including the balanced use of mineralfertilizers as part of an IPNS, and basic knowledge ofthe economics of fertilizer use have to be introduced.

Pricing: price is an important factor in improving theincome of farmers. Whether or not to subsidize theproduct or the inputs in order to stimulate productionhas long been a controversial issue. Most developingcountries in Asia have used input subsidies in agricul-ture; developed countries support farm activities withother mechanisms, often with indirect or invisibleeffects, and not always to stimulate production.Subsidies given directly or indirectly to farmers for fer-tilizers have been the most important pricing factor indeveloping countries. They have been clearly shown to

Policies for effective plant nutrition

Policies for effective plant nutrition should address the

following topics:

● determining the balance between domestic food

production and food imports for countries aiming at

food self-reliance;

● assessing plant nutrient requirements;

● choosing the sources and combinations of plant

nutrient supplies;

● determining domestic production and imports of

fertilizer products and raw materials;

● setting price levels for nutrients vis-à-vis the price of

produce;

● providing distribution, marketing and credit facilities,

including adequate foreign exchange allocation;

● legislation; and

● supporting extension and research (access to

technology).

THE AGENDA FOR EFFECTIVE POLICY

18

policies for effective plant nutrition

increase demand for plant nutrients. Some subsidieshave been misused or carried too far, to the extent ofburdening countries' budgets. Other incentives to fer-tilizer use include guaranteed support prices for agri-cultural produce, duty-free imports of fertilizer, and taxexemptions for credit and investment in fertilizers andcrop production. These measures affect the profitabili-ty of fertilizer use and provide an economic motivationfor increasing crop production.

Legislation: fertilizer legislation deals mostly with spec-ifications on composition, in terms of nutrients andinert material, concentration of plant nutrients, physi-cal properties, package characteristics, labelling andweight, storage and quality control.

Packaging: fertilizer packaging should reduce lossesbut not add substantially to the price of fertilizer. Itshould also convey the right information to users.Fertilizer distribution systems and requirements for

storage and transport condition the quality of fertilizerpackaging. The chemical and physical properties of theproducts and conditions of storage, especially at theend of the distribution chain, must also be considered.

Advice and planning should involve both governmentand the private sector. A focal point for fertilizer adviceand planning is needed to establish a well-integratedfertilizer policy, coordinated with the country's agricul-tural and food-security policies, and in harmony withnational priorities. This focal point can also advise onprices and marketing policy, and be responsible fordemand forecasting and identifying research andextension priorities.

Financing: fertilizer is a product for which demand isoften highly seasonal. Fertilizer traders’ cash flow istherefore highly variable and traders will need com-mercial credit in foreign and domestic currency.

19

Couston, J. W. and Pratap Narayan. 1987. Role offertilizer pricing policies and subsidies in agriculturaldevelopment. Rome, FAO, 31 pp.

FAO. 1972. Effects of intensive fertilizer use on the humanenvironment. FAO Soils Bulletin No. 16, Rome, FAO,360 pp.

FAO. 1985. Economic, financial and budget aspects offertilizer use development. FAO/FIAC FertilizerProgramme No. 3, Rome, FAO, 17 pp.

FAO. 1986. International code of conduct on thedistribution and use of pesticides. Rome, FAO, 28 pp.

FAO. 1987. Fertilizer strategies. FAO Land and WaterDevelopment Series No. 10, Rome, FAO, 148 pp.

FAO. 1993. Technical handbook on symbiotic nitrogenfixation, legume/rhizobium. Rome, FAO,

FAO. 1995. World agriculture: towards 2010. N.Alexandratos (ed.). Chichester, United Kingdom,John Wiley, 488 pp.

FAO. 1995. Integrated plant nutrition systems. R. Dudaland R. N. Roy (eds.) FAO Fertilizer and PlantNutrition Bulletin No. 12, Rome, FAO. 426 pp.

Fertilizer Association of Ireland. 1991. Code of goodpractice for the environment. Dublin, FAI.

IACR. 1988. Keeping the balance, a Rothamsted guide: soiland fertilizer nitrogen. Harpenden, United Kingdom,Institute of Arable Crops Research, RothamstedExperimental Station, 4 pp.

IFA-EFMA. 1990. Code of best agricultural practices tooptimize fertilizer use. International Fertilizer IndustryAssociation/European Fertilizer ManufacturersAssociation, Paris, 4 pp.

MAF. 1991. Code of good agriculture practice for theprotection of water. London, Ministry of Agriculture,Fisheries and Food Publications, 80 pp.

Roy, R. N. 1990. Integrated plant nutrition systems: state ofthe art. Commission on Fertilizers, 11th session, Rome,FAO, 15 pp.

Van Reuler, H., and Prins, W. H., eds.. 1993. The role ofplant nutrients for sustainable food production in sub-Saharan Africa. Leidschendam, The Netherlands, VKP,232 pp.

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