consultants meeting report for crp on irrigation water · presentation on a proposed crp which will...

JOINT FAO/IAEA DIVISION OF NUCLEAR TECHNIQUES IN FOOD AND AGRICULTURE

INTERNATIONAL ATOMIC ENERGY AGENCY FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS

IAEA-Serial Number

WORKING MATERIAL

Managing irrigation water to enhance crop productivity under water-limiting conditions: a role for isotopic

techniques

Report of the FAO/IAEA Consultants Meeting held in Vienna, Austria

26 -29 June 2006

Scientific Secretary: Mr. Minh-Long Nguyen

Reproduced by the IAEA Vienna, Austria, 2007

NOTE

The material in this document has been agreed by the participants and has not been edited by the IAEA. The views expressed remain the responsibility of the participants and do not necessarily reflect those of the government(s) of the designating Member State(s). In particular, neither the IAEA nor any other organization or body sponsoring this meeting can be held responsible for any material reproduced in the document.

EDITORIAL NOTE

In preparing this publication for press, staff of the IAEA have made up the pages from the original manuscripts as submitted by the authors. The views expressed to not necessarily reflect those of the governments of the nominating Members States or of the nominating organizations. Throughout the text names of Member States are retained as they were when the text was compiled. The use of particular designations of countries or territories does not imply any judgment by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA. The authors are responsible for having obtained the necessary permission for the IAEA to reproduce, translate or use materials from sources already protected by copyrights.

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TABLE OF CONTENTS 1. INTRODUCTION .............................................................................................................. 2 2. THE MEETING.................................................................................................................. 3 3. THE PROPOSAL .............................................................................................................. 4 4. CONCLUSIONS................................................................................................................ 4 5. RECOMMENDATIONS................................................................................................... 4 ANNEXES: Annex A - Proposal for a Co-ordinated Research Project Annex B - List of Participants Annex C – Agenda Annex D - Abstracts

1. INTRODUCTION

Competition among different sectors for scarce water resources and increasing public concern on water quality for human health, livestock performance and industrial activities, including tourism have focussed more attention on water management in agriculture. In many parts of the world, the agricultural sector is the predominant user (75-80%) of freshwater resources. Improving water use efficiency in agriculture will require an increase in crop water productivity CWP (i.e. the crop productivity per unit of total water consumption) through the use of novel irrigation technologies and an improvement in water management practices and soil moisture conservation measures at both farm and catchment levels. Limited information is available on: (i) CWP and Transpiration Efficiency TE (i.e. the crop biomass per unit of transpired water) under different irrigation technologies, (ii) the extent and proportion of evapotranspiration (ET) as evaporation, Es, directly from soil surfaces and transpiration from different crops under different irrigation and soil-plant management conditions (e.g., planting density and cropping systems), (iii) sources of water from different soil depths taken by plants and (iv) off-site losses of water through subsurface flows or deep drainage below the root zone under different irrigation conditions. This information is urgently needed to ensure sustainable irrigated agricultural systems. Off-site water losses can occur from either; inappropriate land management practices to capture a substantial part of rainfall within an agricultural landscape and retain it in the rooting zone or excessive use of irrigation water. Such losses not only lead to water wastage but also potential hazards of soil salinity and water pollution resulting from the transport of nitrate, phosphate, sediments and agro-chemicals to receiving water bodies (Hart et al., 2002; Nguyen, 2005). In accordance with the IAEA Programme of Work and Budget 2006-2007, the Soil and Water Management & Crop Nutrition Section (SWMCN) plans to develop a coordinated research project (CRP) under the project E.1.08 to use isotopic, nuclear and associated non-nuclear methods to quantify and better identify the pathways and fate of water (and nutrients) within the soil-plant-atmosphere continuum, under different irrigation systems. This CRP will link closely with and complement the project proposal of the Isotope Hydrology (IH) Section, which focuses on hydrological pathways and fluxes of water and nutrient transport in deep drainage beyond the plant-rooting zone under different irrigation water management practices at the catchment scale. The outcome will be to improve agricultural water use efficiency and crop water productivity and at the same time minimize water wastage through evaporation; deep drainage and off-site runoff, thus reducing/mitigating agricultural impacts on the water quality of adjacent/downstream water bodies. Data obtained from the proposed CRP will be used for refining inputs/parameters and validating/testing of the FAO’s crop water productivity model (CWP-Model) under a wide range of situations. This model (brand name AquaCrop) is a timely response by FAO to the increasing need for a dynamic tool to predict crop water productivity in agricultural production systems. It was developed as an addition to the revised publication FAO Irrigation and Drainage. Paper Number 33 (Doorenbos and Kassam, 1979) to predict crop yield response to water not only under optimal , but also suboptimal (e.g., rain-fed and dry land systems) water supply conditions, where crops are exposed to the risk uncertainties and extreme climatic events, which may provoke a wide range of variations in harvestable product.

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To address the issue of managing water fluxes at different spatial and temporal scales within irrigated agricultural systems, a Consultants Meeting was convened with the objectives to: • Review the state of the art in the assessment of water use in irrigated agricultural

systems in water-limited environments • Identify key research areas related to the use of isotope, nuclear and associated

techniques in the assessment of transpirational and non-transpirational evaporation. • Develop a proposal for a coordinated research project (CRP) on the Management of

Irrigation Water to Enhance Crop Productivity Under Water-Limiting Conditions. 2. THE MEETING A Consultants’ Meeting (CM) on ‘Management of Irrigation Water to Enhance Crop Productivity Under Water-Limiting Conditions: A Role for Isotopic Techniques’ was held at the IAEA Headquarters in Vienna, Austria, over a 4-day period (26-29 June, 2006). The original title of the CM was: ‘Assessing the Impact of Irrigation Management Technologies on Water Use Efficiency and Crop Water Productivity Using Isotopic and Nuclear Techniques’. After the unanimous recommendation of the external consultants it was amended to the above title. Five scientists with international expertise in plant physiology and natural resource management were invited as consultants. In addition, staff from the Soil and Water Management and Crop Nutrition (SWMCN) Section of the Joint FAO/IAEA Division of Nuclear Techniques, representatives from FAO-Rome (Ms. L. Heng) and the FAO Regional Office for the Near East (Mr. M. Bazza) and representatives from the Isotope Hydrology (IH) Section (Mr. A. Garner and Mr. A. Herczeg) of the Division of Physical and Chemical Sciences (NAPC) attended the meeting. The list of participants is given in Annex B. The meeting was formally opened by Mr. M. L Nguyen, Head of the SWMCN Section, since the NAFA Director, Mr. Liang Qu, was not able to attend at the last minute due to his busy schedule. In the Opening Address, Mr. Nguyen welcomed the participants and outlined the scope and objectives of the meeting. In his capacity as scientific secretary for the CM, Mr. Nguyen also provided background information and guidelines on the conduct of the meeting. The second session involved the presentation of past, current and future activities of the SWMCN sub-programme and the use of isotopic/nuclear techniques in integrated soil-water management. The third session was dedicated to the IAEA’s Water Resource Programme and Isotope Hydrology Section. Mr. A. Garner, who represented Mr. P. Aggarwal in his absence, gave an overview of the IAEA’s Water Resource Programme, followed by Mr. Herczeg’s presentation on a proposed CRP which will be initiated by the IH Section to complement the CRP resulting from this CM. In the fourth session, the consultants presented their papers on the various aspects related to crop water use and management. Abstracts of the presentations are given in Annex D. Each presentation was followed by extensive discussion. Four working sessions (Sessions IV-VIII) were organized to discuss and develop future research activities, including project goals, objectives and outputs. A detailed project work plan was discussed and the CRP logical framework and work plan were drafted. A working session was also devoted to the finalization of outcomes and conclusions from the working group sessions and to comment on the draft of the CRP proposal document. During the final working session, the participants formulated conclusions and recommendations. Two

members of the Consultants Team remained for a final day to assist the Scientific Secretary to complete the preparation of this document and associated CRP. 3. THE PROPOSAL The CRP proposal is included in Annex A. 4. CONCLUSIONS The Consultants concluded that: • In many areas of the world, scarcity, caused by increased demands from other sectors

and by periodic droughts, is constraining irrigation water use, the primary user of diverted water worldwide. Improving the productivity of water (WP; production per unit water used) is a paramount objective in areas where supply is limited.

• The consultants believe that there are many opportunities for improving WP and that the focus should be on the many different ways and many entry points for improving WP that exist along the chain from the water source to the harvestable product.

• On this issue, multidisciplinary approach is important, and, while recognizing the critical importance of the social sciences, team work on the physics, biology and engineering of agricultural water use is crucial.

• Water is lost either by evaporation from cropped fields or by runoff and/or drainage. Appropriate irrigation system engineering and management limits the latter losses, but there are still unproductive losses of direct evaporation from the soil (Es) which are largely under the control of the grower. A quantitative approach is therefore required to assess various system components of water use and productivity to identify opportunities for improving WP. Efforts for improving WP should be based on the quantitative evaluation of TE (the amount of biomass produced per unit of water transpired (T)) for different crop species and strategies to minimise Es.

• A number of promising methodologies were identified, several based on the use of isotopes, to improve current assessments of water, carbon and nutrient balances in irrigated agriculture and of WP. Much progress has been made recently and testing a variety of approaches in different agricultural systems is now appropriate.

• It was concluded that there are very good prospects for impacting positively on farm irrigation management in many world areas from the proposed CRP activities.

• The work proposed fits very well within the current thinking and the conceptual models available for improving the productivity of water in agricultural systems, and can contribute to progress in modelling efforts, such as the FAO Aquacrop model.

5. RECOMMENDATIONS Specifically within the objectives of the CRP presented in Annex A, the consultants formulated the following recommendations: • To evaluate the potential for reducing Es, reliable methods to measure Es separate

from T should be developed and tested. • It is recommended that a new effort is launched to quantify TE for different types of

crops and in different environments and that methods are devised to normalize the TE factor for climate variations.

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• To develop novel irrigation management strategies, it is recommended that an improved understanding of the basis for yield determination under limited water is developed. In particular, the consultants recommend that particular attention is placed on the interactions between newer irrigation technologies and the physiological behaviour of crops in relation to yield and quality of marketable products.

• It is recommended that the CRP is an interregional project linking a total of 10-12 African and Asian partners. It is recommended that the CRP duration be 5 yrs, with maximum funding possible per year.

• There should be a workshop for agreeing appropriate protocols and training participants at the beginning of the project, in particular on the new isotopic techniques to separate Es from T.

In addition to the above objectives, a number of priorities were identified for future investigation within the wider theme of agricultural water management in water-limited environments • It is recommended that future efforts address the role of nutrients in both the

achievement of high WP and the efficient use of fertilizers under limited water supply.

• It is also recommended that the areas of water quality, environmental protection and sustainability (groundwater overdraft, salinity issues), receive due consideration beyond the field scale, in situations of water scarcity. Projects should link field measurements to higher scales (up to the catchment), using isotopic/nuclear and related techniques.

• Future projects should apply principles derived and experience gained in this CRP to include rain-fed systems and water conservation and water harvesting as means of improving WP in conditions of water scarcity. Projects should link with supplemental irrigation and related techniques.

• Opportunities exist to include plant improvement and the use of physiology for targeting breeding efforts for high WP under limited water conditions.

ANNEXES

ANNEX A PROPOSAL FOR A CO-ORDINATED RESEARCH PROJECT

1. TITLE OF THE CRP Managing irrigation water to enhance crop productivity under water-limiting conditions: a role for isotopic techniques

2. PROPOSED DURATION: 5 years (2007-2011) 3. JUSTIFICATION Food security and environmental sustainability depend on efficient use of scarce water in agriculture, particularly with the increasing competition for water to meet the needs of urban population, industries and tourisms. Since water is a transport agent of nutrients, agro-chemicals, farm slurries/wastes, and sediment from farm lands to receiving water bodies, improper land and water management practices at farm and catchment levels can potentially affect the quantity and quality of water resources that can be used not only for farming but also for downstream communities (Nguyen and Sukias, 2002; Hart et al., 2004; McDowell et al., 2004). Currently on the average around 75-80% of worldwide fresh water resource is consumed by irrigated agriculture. This level of consumption by agriculture is not sustainable into the future because of the increasing competition for water from other sectors and the variation in rainfall patterns and global warming as a result of climate changes. Approximately one-third of the population of developing countries live in regions where there is insufficient water supplies to meet the expected needs for agricultural, domestic, industrial and environmental purposes in the year 2025 (Seckler et al, 1998). Thus improving water management in agriculture is crucial for increased global food security and alleviating rural poverty. This will require the development and testing of novel water management practices and soil moisture conservation measures at farm and catchment levels as well an increase in crop water productivity (Kijne et al. 2002; Pereira et al. 2002; Turner, 2004). Improving water use efficiency in agriculture can be achieved by: • An increase in crop water productivity (i.e., an increase in marketable crop yield per

unit of water transpired) through the use of novel irrigation technologies. • A decrease in water outflows (e.g., evaporation and deep drainage) from the soil-plant

continuum other than crop stomata transpiration and an increase in soil water storage within the plant rooting zone through better soil and water management and conservation practices at farm and catchment levels.

Novel irrigation technologies include: • Drip irrigation, which targets water applied to the plant rooting zone and minimizes

unnecessary field losses via evaporation, deep drainage and surface runoff. • Deficit irrigation, which involves less water supplied to the crop than would be needed

for achieving maximum crop yield production. Because of the usually curvilinear

shape of the crop-water production function (i.e. the relationship between crop yield and water received by the crop), maximum crop water productivity would be achieved at a water supply that is lower than needed for maximum yield. It has been reported that in Mediterranean climates, deficit irrigation with a water application of 40-70% less than needed for maximum yield resulted in a loss of wheat grain production of only 13% (Zhang and Oweis, 1999).

• Partial root zone drying irrigation in which irrigation water is applied alternatively to furrows or drip lines on either side of row crops (Kirda et al. 1999).

The benefits of novel irrigation technologies in minimizing water wastage are greater when combined with the following soil-plant-water management practices: • Crop scheduling to take advantage of periods with low evaporation. • Synchronizing water application with crop demand to avoid over-irrigation. • Appropriate plant spacing and orientation. • Optimum nutrient management and the use of high value crops to provide high

economic returns per unit of water applied. Integrated soil fertility-water management is critical in determining plant growth, agricultural output and nutrient-water use efficiency. The interaction between water and nutrient is such that the potential benefit of applied nutrients to crop productivity depends on water availability, whereas the effect of water on crop growth and optimum yield production is also determined by the soil fertility status. This interaction is often ignored in economic (cost-benefit) analyses of irrigation and fertilizer applications (Drechsel et al., 2004). It is only through the combined evaluation of the effects of nutrients and water that the actual value of the added nutrients and irrigation water can be measured and the relative benefits and costs of various land and water management options can be assessed. Environmental aspect

Determination of water fluxes at different spatial and temporal scales within and beyond the plant rooting zone remains a formidable challenge because of interactions between water sources from rainfall, irrigation and subsurface water on plant uptake, evaporation, transpiration and transport of water inputs (rainfall or irrigation) into receiving water bodies. To date, the potential to increase the water productivity of crops by maximising the transpired fraction and minimising soil surface losses have not been adequately examined. The involvement of the Agency in the CRP is justified because: a) nuclear/isotopic techniques for tracking and quantifying water fluxes through plant

and soil surfaces are essential for successful implementation of the project. b) without the use of isotopic techniques, processes and pathways of water within the

soil-plant continuum and the efficiencies of different crops in their productive use of water remain uncertain.

c) the outputs of the CRP will contribute to the strategic objectives of the FAO’s Department of Agriculture and, in particular, the development of conceptual models of crop water productivity.

d) the research objectives and expected project outputs are highly relevant to a number of Member States with a need to develop strategic plans for the management of irrigation in water-limited environments.

4. OBJECTIVES 4.1. Overall Objective

To improve the water productivity (production per unit of water input) of crops under water-limiting conditions.

4.2. Specific Research Objectives

4.2.1. Quantify, and develop means to manage soil evaporative losses to maximise the beneficial use of water – the transpirational component of evapotranspiration.

4.2.2. Quantify, and develop means to improve the amount of biomass produced per unit

of transpiration. 4.2.3. Devise irrigation and related management techniques to enhance the yield

component of biomass production (Harvest Index). 5. EXPECTED OUTPUTS 5.1. Field validation of isotopic techniques for quantifying evaporation and transpiration in

crop ecosystems. 5.2. Comparative datasets of evaporation components from different crops and regions. 5.3. Improved estimates of TE (dry matter production per unit of transpiration) of a range of

crop species and in different environments. 5.4. Better strategies to improve the crop production per unit of water used. 5.5. New information (valuable for plant improvement programmes) on the mechanistic

basis of the regulation of crop yield in water-limited environments. 5.6. Data inputs for pilot-testing and validation of FAO water productivity model. 5.7. Enhanced capacity of NARS to conduct applied research on crop water productivity

with the aid of isotopic, nuclear and related techniques. 5.8. Research findings communicated to the wider scientific community for further transfer

to the farmers, which will be the end-users and beneficiaries.

6. WORK PLAN 6.1. Tasks

6.1.1. In relation to specific objective 4.2.1: a) Compare and evaluate underlying assumptions of isotope technique with other

approaches (e.g., microlysemetry, sap flow, soil water balance using neutron probe, etc.) for quantifying soil evaporation and transpiration.

b) Compare evaporation and transpiration fluxes over varying crop types and stages of canopy development, and soil surface wetness.

c) Use the data collected to devise irrigation and related management strategies to minimize evaporation part of evapotranspiration, using FAO’s AquaCrop or similar model for this purpose where appropriate.

6.1.2. In relation to specific objective 4.2.2: a) At selected locations (MS) measure crop biomass and transpiration across a range

of management strategies (nutrient levels, sowing rate and date and variety) for different crop species to calibrate existing transpiration efficiency (TE) predictions.

b) Develop protocols to adjust for surface evaporation, saturation deficit and crop biomass components to refine TE calculations.

c) Validate TE predictions for a range of species and management practices at MS locations.

d) Devise and test management strategies at MS locations to improve crop production per unit of water.

6.1.3. In relation to specific objective 4.2.3: a) Devise and test irrigation management strategies to a) avoid deficits at critical

points in the plant’s development that will impact adversely on yield-determining processes, and b) impose deficits when they will reduce shoot growth but not impact adversely on yield and may enhance harvest index (HI) and/or crop quality.

b) Investigate the fundamental science behind different irrigation management strategies to manipulate shoot and root growth and root hydraulic properties to the benefit of HI and/or crop quality.

c) Assess the suitability of various deficit irrigation techniques (PRD, RDI etc) to deliver strategies defined in 1 and 2 above.

d) Use isotope signals in the soil-plant system to characterize depth and extent of nutrient, and water extraction and water source use by crops.

6.2. Sites & Partners Selection 6.2.1. Contract holders National research systems (NARS) from Africa and Asia with active research programmes on water and irrigation management in crops with expertise and technical capacity to facilitate assessments of evapotranspiration and component fluxes, transpiration efficiency and harvest index.

6.2.2. Technical contracts a) Methods development for atmospheric water vapor sampling and isotopic

analysis (D.G. Williams) b) Development of experimental protocols for measurement of crop biomass and

transpiration efficiency (S. Azam-Ali) c) Data integration, modelling and testing of FAO Aquacrop model (T. Hsiao). d) Evapotranspiration and changes in water isotopic signatures as influenced by crop

residues and carbon sequestration in no-till and conventional agriculture (P. Macaigne)

6.2.3. Agreement holders Advanced research institutions with expertise in the use of isotopic and related techniques for quantifying crop water and carbon balance.

6.2.4. Locations For all crops, target environments would include: • Agroecosystems in which target crops are important for food security • Agroecosystems in which water availability is a principal production constraint

6.3. Timeframe

6.3.1 Meetings and other activities Activity 2006 2007 2008 2009 2010 2011 2012 1. Consultants Meeting (25-28 June, 2006).

Formulation of project proposal and submission for approval to NA subcommittee.

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2. Advertise the CRP. Receipt of research contracts and agreement proposals (by March 2007). Agreements 3-4; Contracts: 8-10; Technical Contracts: 3

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3. Organize 1st RCM (May-June) to discuss overall work plan and establish protocols.

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4. Organize 2nd RCM (November) to evaluate the progress based on progress reports and presentations. Discuss future activities in line with the project objectives.

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5. Organize 3rd RCM (April) to evaluate the results obtained in line with the project objectives. Provision of guidelines for preparation of final reports and manuscript for IAEA-TECDOC or external publications.

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6. Organize the final RCM (September) to present final reports. Achievements of the CRP will be evaluated and conclusions drawn. Formulate recommendations for future research. Preparation of the final report of the CRP.

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7. Preparation of IAEA-TECDOC and other publications for dissemination of information gathered during the CRP.

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7. FINANCIAL INPUTS Item 2007 2008 2009 2010 2011 2012 Research Contracts 100,000 100,000 100,000 100,000 100,000 Technical Contracts 20,000 20,000 20,000 20,000 Co-ordination Meetings 45,000 45,000 45,000 45,000 Total 165,000 165,000 120,000 165,000 145,000 10,000 8. ASSUMPTIONS a) Adequate research teams established and field and laboratory facilities available to

conduct the programmed research. b) Research not interrupted by catastrophic climatic or other events. c) Research contract obligations fulfilled. d) Agreement holders will provide strategic support to implement the main elements of the

project. e) Continuity of CRP management and funding provided by IAEA. 9. PROJECT LOG FRAME

Narrative summary Verifiable indicators Means of verification Assumptions Goal (overall objective): To improve the water productivity (WP-production per unit of water input) of crops under water-limited conditions

Member states (MS) have enhanced capacity and better access to improved techniques and strategies for assessing and increasing water productivity

Reports of contract & agreement holders. Manuscripts, technical bulletins, & web-based information available to all MS

Project participants are dedicated and have the capacity to carry out project tasks, apply the technology, and report findings

Purpose (specific objectives): 1. Quantify, and develop means to manage soil evaporative losses to maximise the beneficial use of water – the transpirational com-ponent of evapo-transpiration (ET)

2. Quantify, and develop means to improve the amount of biomass produced per unit of transpiration

3. Derive additional data and devise irrigation and related management techniques to enhance yield

1. Appropriately collected samples for isotopic analysis, evaporation/ transpiration data for target crop(s), and relationships between transpiration/evaporation and irrigation/rainfall and other biophysical variables. Appropriate plans for reducing evaporation losses based on quantified water fluxes and other available information

2. WP data sets derived from project for different species

3. Datasets and packages of irrigation protocols for different crops in different environments

Project reports, manuscripts, presentations of results at meetings, technical bulletins, web-based information and data on: - Evaporation, transpiration, & soil water balance

- water productivity - yield

1. Project participants have the capability and proper instrumentation to conduct measurements and quantify water balance and fluxes.

2. Project participants pro-vide high quality data of all components of total biomass, transpiration and relevant meteoro-logical variables.

3. IAEA provides resources for the centralised integration and sharing of databases

Narrative summary Verifiable indicators Means of verification Important assumptions Outputs: 5.1.1. Field validation of isotopic techniques for quantifying evaporation and transpiration in crop ecosystems 5.1.2. Comparative datasets of evaporation components from different crops and regions 5.1.3. Improved estimates of TE (dry matter production per unit of transpiration) of a range of crop species and in different environments 5.1.4 Better strategies to improve the crop production per unit of water used 5.1.5. New information (valuable for plant improvement programmes) on the mechanistic basis of the regulation of crop yield in water-limited environments 5.1.6. Data inputs for pilot-testing and validation of FAO water productivity model 5.1.7. Enhanced capacity of NARS to conduct applied research on crop water productivity with the aid of isotopic, nuclear and related techniques 5.1.8. Research findings communicated to the wider scientific community for further transfer to the farmers, which will be the end-users and beneficiaries

Data from two or more independent techniques including isotopic technique for partitioning evapotranspiration Data on evapotranspiration components and associated biophysical variables from different environments and crops Data combined with existing information on crop TE values Recommendations for irrigation of different crops in different environments Additional information for fine-tuning of irrigation strategies and plant breeding programmes based on new understanding Meta-data centralised and shared from web site Increased number of publications/reports on water productivity and crop water balance using isotopic, nuclear and related techniques Published papers, abstracts, web-based reports, etc. documenting outcome

Reports of contract & agreement holders. Manuscripts, technical bulletins, & web-based information available to all MS

Partner institutions have dedication and technical capability to provide expected outputs IAEA provides resources for the centralised integration of databases Continued interaction with FAO on water productivity model

10. BRIEF DESCRIPTION FOR THE IAEA BULLETIN Water limitation and drought threaten food security in many regions worldwide, and demands on limited water supplies for crop irrigation often are in sharp conflict with other needs. Water productivity (WP - biomass produced per unit of water input) and yield of crops varies substantially. However, underlying controls on WP and yield, even where other factors such as soil nutrient supply are not limiting, are poorly characterized for many water-limited situations. Crop transpiration efficiency (TE) and harvest index (HI), two important components of WP and yield, have not been adequately quantified under a range of water-limited conditions for important crop species. Therefore, the most optimal strategies for enhancing crop production with limited water through irrigation management have not been developed. This CRP will provide improved understanding and quantification of the non-productive component of crop evapotranspiration, soil evaporation, transpiration efficiency, harvest index and yield under a variety of environments for several important crop species. The information will be used to refine crop production models that are essential for optimising irrigation inputs under water limitation. 11. SELECTED REFERENCES Bonachela, S., F. Orgaz, F.J. Villalobos, and E. Fereres. 2001. Soil evaporation from drip

irrigated olive orchards. Irrig. Sci. 20(2):65-71. Doorenbos, J.,Kassam,, A. H. 1979: Yield Response to Water. FAO’s Irrigation and

Drainage. Paper Number 33. Drechsel, P., Giordano, M.and Gyiele, L. 2004. Valuing nutrients in soil and water: concepts

and techniques with examples from IWMI studies in the developing world. Research Report 82, International Water Management Institute, Colombo, Sri Lanka.

Fereres, E. , D.A. Goldhamer, and L.G. Parsons. 2003. Irrigation Management of Fruit Trees. Centennial Issue of the American Society of Horticultural Science. HortScience 39(5):1036-1042.

Hart, M. R., Quin, B. F., Nguyen, M. L. 2004. Phosphorus runoff from agricultural land and direct fertilizer effects: A review. Journal of Environmental Quality 33: 1954-1972.

Kijne, J.W., Tuong, T. P., Bennett, J., Bouman, B., Oweis, T. 2002. Ensuring food security via crop water productivity improvement. International Water Management Institute, Colombo, Sri Lanka. (http://www.iwmi.org/challengeprogram/).

Kirda, C., Moutonnet, P., Hera, C., Nielsen, D.R. (Eds) 1999. Crop yield response to deficit irrigation. Kluwer Academics Publishers, The Netherlands.

McDowell, R. W., Biggs, B. J. F.; Sharpley, A .N., and Nguyen, L 2004. Connecting phosphorus loss from agricultural landscapes to surface water quality: A review. Chemistry and Ecology 20: 1-40.

Nguyen, L; Sukias, J. 2002. Phosphorus fractions and retention in drainage ditch sediments receiving surface runoff and subsurface drainage from agricultural catchments in the North Island, New Zealand. Agriculture, Ecosystems and Environment 92: 49-69.

Pereira L.S., Oweis, T., Zairi, A. 2002. Irrigation management under water scarcity. Agric. Water Manag. 57:175-206.

Seckler, D. W., Amarasinghe, U., Molden, D., de Silva, D., R., Barker, R. 1998. World water demand and supply, 1990-2025: scenarios and issues. Research Report 19, International Water Management Institute, Colombo, Sri Lanka.

Turner, N.C. 2004. Agronomic options for improving rainfall-use efficiency of crops in dryland farming systems. J. of Exp. Bot. 55(407): 2413-2425.

Williams, D.G., W. Cable, K. Hultine, J.C.B. Hoedjes, E. Yepez, V. Simonneaux, S. Er-Raki, G. Boulet, H.A.R. de Bruin, A. Chehbouni, O.K. Hartogensis and F. Timouk. 2004. Components of evapotranspiration determined by stable isotope, sap flow and eddy covariance techniques. Agricultural and Forest Meteorology 125:241-258.

Zhang, H., Oweis, T. 1999. Water-yield relations and optimal irrigation scheduling of wheat in the Mediterranean region. Agricultural Water Management 38: 195-211.

Annex B - LIST OF PARTICIPANTS External consultants: Dr. William Davies (Co-Director) Lancaster Environment Centre, Lancaster

University, UK, [email protected]

Dr. Dave Williams (Professor) Department of Renewable Resources, University of Wyoming, USA, [email protected]

Dr. Theodore Hsiao (Professor) Professor of Water Science and Plant Physiologist, Department of Land, Air and Water Resources, University of California, Davis, USA, [email protected]

Dr. Ellias Fereres Castiel (Professor) University of Cordoba, Spain, [email protected]

Dr. Sayed Azam-Ali (Reader) Reader in Tropical Agronomy, Division of Agricultural & Environmental Sciences School of Biosciences, University of Nottingham, UK, [email protected]

FAO Representative Dr. Mohamed Bazza Senior Irrigation and Water Resources Officer, FAO

Regional Office for the Near East, Cairo, Egypt, [email protected]

Dr. Lee Heng FAO Consultant, FAO Consultant-Ex-IAEA staff member, [email protected]

Scientific Secretary Mr. Long Nguyen Section Head, Soil and Water Management & Crop

Nutrition Section (SWMCN), Joint FAO/IAEA Division, Vienna, Austria, [email protected]

Joint FAO/IAEA Division Mr. Long Nguyen (Section Head) SWMCN Section Mr. Felipe Zapata (Technical Officer) SWMCN Section Mr. Emil Fulajtar (Technical Officer) SWMCN Section Mr. Gudni Hardarson (Unit Head) Soil Science Laboratory Unit (Seibersdorf) Mr. Joseph Adu-Gyamfi (Technical Officer) Soil Science Laboratory Unit (Seibersdorf) Mr. Lionel Mabit (Technical Officer) Soil Science Laboratory Unit (Seibersdorf)

ANNEX C – AGENDA

Consultants Meeting on

“Assessing the Impact of Irrigation Management Technologies on Water Use Efficiency and Crop Water Productivity Using Isotopic and Nuclear

Techniques” 26 – 29 June 2006

Vienna International Centre Meeting Room B0513

Scientific Secretary: Mr. Long Nguyen

Administrative Assistant: Ms. Eveline Kopejtka

PROGRAMME

Monday, 26 June 2006

Session I Opening Session

09.00-09:10 Brief Introduction: Mr. Long Nguyen, Head, Soil and Water Management & Crop Nutrition Section Head, FAO/IAEA Soil and Water Management & Crop Nutrition subprogramme

09:10-09:25 Official Opening: Mr. Liang Qu, Dir-NAFA (Nuclear Applications in Food and Agriculture)

09:25-10:30 Mr. Long Nguyen

Food and Agriculture Organisation of the United Nations

Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture Wagramer Strasse 5, P.O. Box 100, A-1400 Vienna, Austria Phone: (+43 1) 2600 • Fax: (+43 1) 26007 E-mail: [email protected] • Internet: http://www.iaea.org In reply please refer to: 311.D1.05CT05720 Dial directly to extension: (+431) 2600-21647

Scope and objectives of the Consultant Meeting 10:30-11:00 Coffee break Session II IAEA-FAO projects on water management in Agriculture

Chairperson: Mr. Gudni Hardarson, Head, Soil Science Unit-Seibersdorf

11:00-11:30 Mr. Long Nguyen Water Management in Agriculture-The use of isotopic/nuclear techniques in current and future research activities.

11:30-12:30 Ms. Lee Heng, FAO Consultant-Ex-IAEA staff member Water Management in Agriculture: Past Activities in the Soils FAO/IAEA Subprogramme and its contribution to FAO-Crop Water Productivity Model.

12:30-14.00 Lunch and Completion of Administrative Matters-Ms. Eveline Kopejtka

14:00-15:00 Mr. Mohamed Bazza FAO-Senior Irrigation and Water Resources Officer, FAO Regional Office for the Near East in Cairo, Egypt. Pathways for Improving Crop Water Productivity and Water Use Efficiency

15:00-15:30 Coffee break

15:30-16:00 Mr. Felipe Zapata - Mr. Joseph Adu-Gyamfi IAEA-Soil and Water Management & Crop Nutrition Subprogramme Crop selection for greater water productivity and adaptation to abiotic stresses using isotopic techniques.

Session III IAEA’s Water Resource Programme-Isotope Hydrology Section Chairperson: Mr. Long Nguyen

16:00-16:30 Mr. Pradeep Aggarwal IAEA Water Resources Programme and Head of the Isotope Hydrology Section

General Aspects of IAEA’s Water Resources Programme 16:30-17:30 Mr. Andrew Herczeg, IAEA, Isotope Hydrology Section

A new CRP based on a CM: Develop geochemical and isotope techniques to evaluate the water flux below the root zone in irrigation systems.

17:30-19:00 IAEA Reception- Ms. Eveline Kopejtka Tuesday, 27 June 2006 Session IV International perspective on irrigation technologies, crop water

productivity and water use efficiency Chairperson: Mr. Mohamed Bazza

09:00-10:00 Mr. William Davies, Prof., Co-Director of Lancaster Environment Centre, Lancaster University, U.K. Understanding the impacts of deficit irrigation to sustain yield while enhancing water and nutrient use efficiencies

10:00-11:00 Mr. Sayed Azam-Ali, Reader, Division of Agricultural & Environmental Sciences School of Biosciences, University of Nottingham, U. K. Precision, accuracy and sense in measuring soil moisture content in vegetation

11.00-11:30 Coffee break 11:30-12:30 Mr. Ted Hsiao, Prof., Department of Land, Air and Water

Resources, University of California, Davis, U. S. A. Some unresolved issues in evaporation relative to transpiration and in crop water use efficiency

12.30-13:45 Lunch break Session IV (continued) 13:45-14:45 Mr. Elias Fereres, Prof., University of Cordoba, Spain

Research needs for increasing water productivity in irrigation of

fruit trees and vines 14.45-15:45 Mr. David Williams, Prof., Department of Renewable Resources,

University of Wyoming, U.S.A. Partitioning evapotranspiration from stable isotopes of atmospheric water vapor

15:45-16:00 Coffee break

16:00-17:00 Mr. William Davies, Prof., Co-Director of Lancaster Environment Centre, Lancaster University, U.K.

Critical Research Issues in Crop Water Productivity and Sustainable Water Use for Agriculture

17:00-18:00 Long Nguyen 1. Brief Summary of all the consultants’ presentations. 2. Important framework for Day 3-What are expected activities

and outcomes for Day 3 3. Brief presentation of CRP framework (research contract

holders, agreement holders and technical contract holders) Wednesday, 28 June 2006 Session V Working Session I: Deliberation on Future Research Activities

Chairperson: Ted Hsiao Rapporteurs: David Williams and Sayed Azam-Ali

09:00-10:30 Working Groups: Round-table discussions 10:30-11:00 Coffee break

11:00-12.30 Working Groups: Round-table discussions 12:30-13:30 Lunch break

Session VI Working Session II: Formulation of the CRP proposal-Part 1-CRP objectives Chairperson: Lee Heng Rapporteurs: Williams Davies and Elias Fereres

13:30-15:30 CRP: Title, Objectives, Outputs and Nuclear/Isotopic Components 15:30-16:00 Coffee break

16:00-17:00 CRP: Research tasks and methodologies 17:00-18:00 CRP: Research tasks and methodologies (continued) A.1.1. 18: 30 Dinner at a restaurant: Ms. Eveline Kopejtka

Thursday, 29 June 2006 Session VII Working Session III: Formulation of the CRP-Part 2- CRP

work plan Chairperson: Mohamed Bazza Rapporteurs: Lee Heng and Gudni Hardarson

08:30-09:30 CRP: Log frame of the CRP and Establishment of Guidelines 09:30-10:30 CRP: Log frame of the CRP and Establishment of Guidelines

(continued) 10:30-11:00 Coffee break

Session VIII Finalization of project document and recommendations Chairperson: Long Nguyen Rapporteurs: David Williams and Sayed Azam-Ali

11.00-12.30 Draft conclusions and recommendations from the Consultants regarding the CRP

12:30-13:30 Lunch break

13:30-14:30 Preparing a draft of project document (Report of the FAO/IAEA consultants)

14:30-15:30 Preparing a draft of project document (continued) 15:30-16:00 Coffee break

16:00-17:00 Discussion and adoption of the draft project document and recommendations

17:00 Closing of the Meeting

ANNEX D – ABSTRACTS Partitioning evapotranspiration from stable isotope measurements of atmospheric water vapor David Williams Department of Renewable Resources University of Wyoming, USA E mail: [email protected] Management of scarce water supplies in arid and semi-arid regions for agriculture and other important societal needs requires a better understanding and accounting of evapotranspiration (ET). It is difficult to distinguish plant transpiration from soil evaporation, and so the bulk flux ET is normally considered. However, evaporation and transpiration are influenced by different biological and physical processes, and thus independent estimates of these component fluxes are needed to account for variation in ET and constrain model predictions. Isotope measurements of atmospheric water vapor in the mixed boundary layer in crop canopies and in natural vegetation are being used to partition ET into component fluxes providing novel insight into processes driving system water and carbon exchange. Three approaches can be employed for this purpose: 1) the flux gradient method (Yakir and Wang 1996), the ‘Keeling plot’ method (Yakir and Sternberg 2000, Williams et al. 2004), and the relaxed eddy accumulation (REA) method (Bowling et al. 1999). The flux gradient method provides direct estimates of the flux rates of transpiration and evaporation, whereas the Keeling plot technique provides only estimates of the fractional contribution of these flux components to the total ET flux, and thus requires independent measurements of ET by other means. Approaches for partitioning ET based on the stable isotope ratios of atmospheric water vapor are useful for monitoring short-term (hours, days) changes in ET and component fluxes, and have the potential to distinguish multiple transpiration sources in mixed vegetation communities. Studies with olive in Morocco (Williams et al. 2004) demonstrate the use of the Keeling plot technique for documenting daily changes in soil evaporation following surface irrigation. Keeling plot measurements in a savanna ecosystem in the semiarid Southwestern US were used to partition transpiration from woody overstory plants from that of understory forage grasses (Yepez et al. 2003). Chamber based methods using Keeling plots of water vapor (Yepez et al. 2005) can be useful where requirements for the proper application of micrometerological approaches are not met, such as in plot-level experiments or field trials of different crop varieties. A number of uncertainties exist in the estimation of isotopic values for component ET fluxes. Most notably, the assumption of isotopic steady-state transpiration is not valid in all situations. Large deviations in the isotopic composition of transpired water relative to plant source water may produce error in partitioning the ET flux based on isotopic mass balance of atmospheric water vapor (Yepez et al. 2005). Estimating the isotopic composition of soil evaporation requires sampling soil water or modeling the evolution of isotopic changes in the soil through time (Braud et al. 2005). Both have limitations and advantages.

Approaches for partitioning ET based measurements of the isotopic composition of atmospheric water vapor are developing rapidly and offer a flexible alternative to other techniques. Such approaches can provide important information necessary to optimize scarce water supplies in arid and semi-arid regions and constrain crop water models. References cited Bowling, D.R., A.C. Delany, A.A. Turnipseed, D.D. Baldocchi, and R.K. Monson. 1999.

Modification of the relaxed eddy accumulation technique to maximize measured scalar mixing ratio differences in updrafts and downdrafts. Journal of Geophysical Research 104:9121-9133.

Braud, I. T. Bariac, J.P. Gaudet, and M. Vauclin. 2005. SiSPAT-Isotope, a coupled heat, water and stable isotope (HDO and (H218O) transport model for bare soil. Part I. Model description and first verifications. Journal of Hydrology 309:277-300.

Williams, D.G., W. Cable, K. Hultine, J.C.B. Hoedjes, E. Yepez, V. Simonneaux, S. Er-Raki, G. Boulet, H.A.R. de Bruin, A. Chehbouni, O.K. Hartogensis and F. Timouk. 2004. Components of evapotranspiration determined by stable isotope, sap flow and eddy covariance techniques. Agricultural and Forest Meteorology 125:241-258.

Yakir, D., Sternberg L.S.L. 2000. The use of stable isotopes to study ecosystem gas exchange. Oecologia 121:297–311.

Yakir D. & Wang X.F. 1996. Fluxes of CO2 and water between terrestrial vegetation and the atmosphere estimated from isotope measurements. Nature 380:515-517.

Yepez E.A, Williams D.G., Scott R.L., Lin G. 2003. Partitioning overstory and understory evapotranspiration in a semiarid savanna woodland from the isotopic composition of water vapor. Agricultural and Forest Meteorology 119:51-68.

Yepez, E.A., T.E. Huxman, D.D. Ignace, N.B. English, J.F. Weltzin, A.E. Castellanos and D.G. Williams. 2005. Dynamics of transpiration and evaporation following a moisture pulse in semiarid grassland: a chamber-based isotope method for partitioning flux components. Agricultural and Forest Meteorology 132:359-376.

Water Management in Agriculture: Past Activities in the Soils FAO/IAEA Sub-programme and the FAO-Crop Water Productivity Model Lee Heng FAO Consultant Rome, Italy E mail: [email protected] Increasing food demand and competition from various sectors for water has made it necessary to improve crop water productivity. This is achievable but it requires concerted effort from all aspects including: Improved methods of irrigation, Deficit or supplemental irrigation, improved soil water management practices, improved soil fertility, improved crop varieties, training and providing guidelines. This presentation illustrates all the above-mentioned aspects using case studies carried out in the Soils FAO/IAEA Sub-programme. An example of improved irrigation method was given from IAEA’s TC regional project on West Asia where a four-year study carried out in Syria comparing the traditional method of irrigation (surface irrigation) and fertilization (soil applied) with fertigation which is the application of water and nutrients through irrigation system. The results showed that cotton seed yield increased more than 30% and WUE increased by 100% comparing surface irrigation to fertigated treatment and increase farmers income by $1000/ha/year. Increasing crop productivity in rainfed arid and semi-arid areas is difficult because of the low and unpredictable rainfall and soils deficient in plant nutrients. Using the cases of Jordan and Morocco in the rainfed CRP, it demonstrated that through tactical management (early sowing), supplemental water management, yield and WUE of wheat can actually be improved. The study also showed that the relationship between grain yields of wheat in the rainfed CRP and ∆ was positively correlated. Similarly the WUE of wheat was also found to be positively correlated with ∆. Under irrigated conditions, yield and N use efficiency are much higher compared to under rainfed agriculture especially when N was also applied. This was illustrated using data from irrigated wheat CRP. Soil water measurement is key to successful water and nutrient management. Accurate, fast and ease of use as well as the ability to do profile measurement are the desirable characteristics needed for routine large scale soil water monitoring. A comparison of the traditionally use soil moisture neutron probe (SMNP) with non-nuclear techniques was needed to formulate recommendations and establish guidelines for IAEA’s current and future soil water research and training programmes. Results of the comparison and factors affecting selection of choices were presented. Training and capacity building also plays an important role in indirectly improving water productivity in agriculture. The types of training provided by IAEA were highlighted. The isotopic signatures as surrogates and selection criteria for WUE was also utilized to investigate if there is genotypic differences in stomatal and TE responses during drought stress between different wheat genotypes. A dry-down experiment was carried out to investigate the relationships between transpiration, transpiration efficiency, fraction of transpirable soil water (FTSW) and carbon isotope discrimination of nine wheat genotypes, by plotting the fraction of transpirable soil water (FTSW) for each drought-stressed treatment against the normalized transpiration ratio (NTR). The results indicate that there was

significant genotypic variation in the WUE and ∆ signatures when genotypes were well-watered and drought-stressed. The drought-stressed treatment caused a decrease in ∆. There was a negative correlation between ∆ and WUE and between TE and ∆ for both treatments. On the other hand, the relationship between Ci, the threshold value of FTSW at which transpiration began to decline was found to be positively correlated with ∆. These results showed that ∆ can be used to select for TE and WUE among young vegetative wheat plants. For more than twenty years, the FAO Irrigation & Drainage Paper n. 33 (Doorenbos and Kassam, 1979) represented an important reference for the estimate of yield response to water of field, vegetables and tree crops. However, significant scientific and experimental progresses have been made in the crop-water relations since its publication. Together with a demand for a higher accuracy in the estimates, means that an update to the approach in Paper n. 33 is necessary. The revision process includes the development of a water-driven dynamic model for field crops and guidelines for tree crops. The model separates the final yield into biomass and harvest index, and also separates crop evapotranspiration (ET) into soil evaporation and crop transpiration. Biomass accumulation over time is the result of the product of water productivity or WUE coefficient (Wp) and cumulated canopy transpiration (Ta) over the same time interval (de Wit, 1958). Steduto and Albrizio (2005) showed that when transpiration is normalized for reference crop evapotranspiration (ETo) for climatic differences, the slope (Wp) of the relationship between above-ground biomass and normalized ET clearly separate C3 and C4 crop groups, with Wp values of 13.4 and between 25 and 32.9 g/m2, respectively. Nitrogen status plays an important role in the slope of Wp for C4 crops (sorghum). Data from IAEA and ICASA for various C3 and C4 were used to verify the above observations, with very good agreement obtained between the Steduto and Albrizio (2005) slopes and the simulated results. Verification of the above approach was presented for maize, chickpea, peanut, soybean and wheat, by comparing measured against simulated biomass and grain yield from DSSAT. References de Wit, C.T., 1958. Transpiration and crop yields. Agricultural Research Reports 64.6,

Wageningen, Pudoc, 88 pp. Doorenbos, J., Kassam, A.H., 1979. Yield response to water. Irrigation and Drainage Paper

no. 33, FAO, Rome, Italy, 193 pp. Steduto, P., Albrizio, R., 2005. Resource use efficiency of field-grown sunflower, sorghum,

wheat and chickpea II. Water use efficiency and comparison with radiation use efficiency. Agric. For. Meteorol. 130, 269-281

Pathways for Improving Crop Water Productivity and Water Use Efficiency Mohamed Bazza Senior Irrigation and Water Resources Officer FAO Regional Office for the Near East Cairo, Egypt E mail: [email protected] The presentation gives an overview of the main water-related issues facing agricultural production and food security, with a focus on the Near East as the driest region of the world. These issues concern water supply, water quality degradation, low governance, declining investment, and weak water management capacity. Highlighting FAO’s forecast regarding future food needs increase and the expected role of irrigation in filling them while the traditional policy to respond to increased water demand through supply expansion presents only a limited potential, the presentation evidences the need for countries to adopt agriculture water demand management and gives an overview of its inferences, particularly: 1) Improving productive efficiency of agriculture water use; 2) Removing policy constraints; 3) Filling water shortage gap through the use of non conventional water resources and virtual water; and 4) Reversing the trend of investment decrease in water resources and agriculture. The presentation then focuses on the potential and the means for achieving agriculture water productive efficiency improvement under both irrigation and rainfed conditions, in addition to the requirements for doing so and the farm and plant levels. Illustrations of the demonstrated potential are also given, focusing on the scenarios of profit maximization and crop yield optimization. The ingredients of an optimal irrigation strategy for achieving optimal water use for profit or yield, notably an appropriate crop yield model, on one hand, and adapted irrigation technology and management, on the other, are also described. Similarly research challenges in general and specific research needs under the project are presented. The presentation finally gives recommendations for the Coordinated Research Project (RCP) under preparation and indicates potential collaborative mechanisms between FAO and the Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture for its implementation.

Deficit Irrigation of Fruit trees and Vines: Research Needs for the Optimal Management of Water Deficits Elias Fereres IAS-CSIC and University of Cordoba 14080-Cordoba, Spain E mail: [email protected] Beneficial use of water in irrigated agriculture includes the full consumptive use (ET) of crops and the leaching fraction for control of salinity. Until recently, the paradigm of irrigation management was to supply sufficient water to meet the full ET needs and the leaching fraction. In many world areas, scarcity caused by increased demands from other sectors of society and by periodic droughts, is shifting the irrigation management paradigm from full to partial supply of the crop water requirements through deficit irrigation (DI). Deficit irrigation is the application of irrigation water below the crop ET requirements, and its use is based on knowledge of the crop response to water deficits. Therefore, DI has to make use of all the relevant information developed on the ecophysiological and agronomic responses to water stress. One trend already observed in irrigation in many water scarce areas is the emphasis on horticulture, for two major reasons. One, is that the water productivity (WP, $/m3) of horticultural crops is much higher than that of field crops and can justify better the use of limited irrigation water. The other is that the yield and profit responses of many fruit trees and vines to variable water supply are less dependent on achieving maximum yields than the major cereal crops. In other words, the maximum profits of many horticultural crops are not tied to achieving maximum water use. Specifically, research has uncovered the potential of Regulated Deficit Irrigation (RDI) as a technique to reduce irrigation water use in tree crops and vines without reducing farm profits. Knowledge on how to apply RDI to the different crops is currently under development, but its potential has already been demonstrated at the commercial orchard scale under very specific conditions and crops, such as peach, almonds, plums and wine grapes. The major research needs to make progress on the application of DI to fruit trees and vines include: a) Development of Best Management Practices in RDI, based on uncovering the physiological and yield responses of the major fruit tree and vines to water deficits; b) Determination of the ET of orchards under water deficits and of the associated gross and net water savings (reduced applied irrigation water and reduced ET) through RDI; c) Design of irrigation scheduling programmes for RDI and associated monitoring and automation needs, using plant and soil based indicators; d) Assessment of the sustainability of RDI by evaluating the salinity and other risks under deficit irrigation; and, e) Determining the pathways for scaling RDI up to Irrigation Scheme management. Selected references Boland, A.M, P.H. Jerie, P.D. Mitchell, and I. Goodwin. 2000. Long-term effects of restricted

root volume and regulated deficit irrigation on peach: II. Productivity and water use. J. Amer. Soc. Hort. Sci. 125(1):143-148.

Bonachela, S., F. Orgaz, F.J. Villalobos, and E. Fereres. 2001. Soil evaporation from drip irrigated olive orchards. Irrig. Sci. 20(2):65-71.

Ebel, R.C., E.L. Proebsting, and R.G. Evans. 1995. Deficit irrigation to control vegetative

growth in apple and monitoring fruit growth to schedule irrigation. HortScience 30(6):1229-1232.

Fereres, E., D.A. Goldhamer, and L.G. Parsons. 2003. Irrigation Management of Fruit Trees. Centennial Issue of the American Society of Horticultural Science. HortScience 39(5):1036-1042.

Goldhamer, D.A. and M. Salinas. 2000. Evaluation of regulated deficit irrigation on mature orange trees grown under high evaporative demand. Proc. Intl. Soc. Citrucult. IX Congress p. 227-231.

Naor, A., H. Hupert, Y. Greenblat, M. Peres, A. Kaufman, and I. Klein. 2001. The response of nectarine fruit size and midday stem water potential to irrigation level in stage III and crop load. J. Amer. Soc. Hort. Sci. 126(1):140-143.

Testi L, F.J. Villalobos, F. Orgaz. 2004a. Evapotranspiration of a young irrigated olive orchard in southern Spain. Agric For Meteorol 121(1-2): 1-18.

Beginning to understand the impact of deficit irrigation to sustain yield while enhancing water and nutrient use efficiencies Bill Davies Lancaster Environment Centre, Lancaster University Lancaster,UK E mail: [email protected] Introduction Of all the biotic and abiotic stresses impacting on crops, drought stress provides easily the greatest limitation to biomass production (e.g. Kramer and Boyer 1995). Biomass accumulation by plants is linearly related to the amount of radiation intercepted by the crop (Monteith 1977). The development of the leaf canopy is critical to intercept radiation, particularly in young developing crops which have not yet covered the soil. Leaf expansion is highly sensitive to soil drying even when there is still substantial water available in the soil profile. Under many circumstances, leaf cell turgor can be significantly reduced as the soil dries and it is undeniable that such changes will greatly restrict plant growth rate (Hydraulic growth limitation). Although genetic manipulations of several components of the plant’s turgor regulating capacity have kept plants alive for longer at low soil water potentials, this response is not commonly accompanied by sustained growth and production at levels that will be of commercial significance (e.g. Kishor et al. 1995). This should not be surprising, however, as a number of research groups have demonstrated that leaf expansion of plants grown in drying soil can be decreased even when shoot water status is maintained (reviewed in Davies and Zhang 1991). In such situations, chemical signals generated as a result of the interaction between root systems and drying soil can directly inhibit leaf growth and reduce plant water loss (Chemical growth limitation). Manipulation of plants to enhance growth in drought stressed environments will have to overcome both chemical limitation and hydraulic limitation of growth. We have shown that as soil dries, shoot water status can be sustained by signalling-induced restrictions in stomatal aperture (Mingo et al. 2003; Sobeih et al. 2004). If in addition to this, we can develop genotypes which do not produce chemical leaf growth inhibitors as soil dries or have leaf growth processes that are insensitive to these signals, then we can perhaps optimise biomass accumulation and yield of vegetative plant parts in dryland agriculture. This strategy is dependent on identifying the chemical signals that limit both stomatal conductance and leaf expansion during drought. While decreased plant water use (caused by the limitation to both stomatal conductance and leaf expansion) can allow the plant to maintain turgor, another strategy might be for the roots to explore deeper parts of the soil profile (Reid and Renquist 1997). Manipulation of this variable may provide extra water supply to growing shoots and allow maintenance of shoot growth processes at low bulk soil water status. In nearly all of the long distance signalling work conducted to date the focus has been almost exclusively on intra-plant signalling. It is clear that soils can contain high concentrations of the same signalling agents that have proved to be effective within the plant in the regulation of growth and function. It is important therefore to quantify potential soil to plant signals and assess the impact of modification of this signalling pathway on the growth and functioning of the plant.

ABA as a regulator of stomatal behaviour and shoot growth Drought increases the ABA concentration of roots and xylem sap (Zhang and Davies 1989). A central role for ABA in the control of stomatal conductance under drought is now generally accepted (Wilkinson and Davies 2002; Dodd 2003) but the role of ABA in the regulation of leaf growth under drought is much less clear. Perhaps the most convincing evidence that ABA restricts leaf growth of droughted plants is the excellent correlation between leaf elongation rate and xylem ABA concentration in plants subjected to soil drying or ABA feeding (Ben Haj Salah and Tardieu 1997). Soil-drying induced increases in xylem pH allow extremely low concentrations of ABA (typical of well-watered plants) to inhibit leaf growth (Bacon et al. 1998). In contrast, at low tissue water potential, ABA accumulation is apparently required to sustain leaf growth (Sharp 2001) and this is also the case in plants subjected to other environmental stresses such as soil compaction (e.g. Hussain et al. 2000). Ethylene as a regulator of leaf and root growth under drought Drought also increases root and xylem concentrations of the ethylene precursor ACC (1-aminocyclopropane-carboxylic acid) (Gomez-Cadenas et al. 1996). Although the delivery of ACC from the root system can account for shoot ethylene evolution (Else and Jackson 1998) and may thus limit leaf growth under drought, the relationship between xylem ACC concentration and leaf growth of plants exposed to drying soil has not been defined. We have recently shown that both xylem ACC and ABA concentrations increase prior to any decrease in shoot water status. It is therefore appropriate to assay the interaction between these two hormones on leaf expansion using well-hydrated plants. Feeding ABA and ACC simultaneously via the xylem to detached shoots inhibits leaf growth additively (Dodd and Davies, unpublished results), suggesting an important role for ethylene in the inhibition of leaf growth in drying soil, when shoot water status is maintained. In contrast, in plants at low water potential, ABA accumulation is necessary to minimise runaway ethylene synthesis and ethylene-mediated root growth inhibition (Sharp 2001). The plant hormone ethylene can be involved in both the suppression of root growth during soil drying and the suppression of leaf growth via long-distance chemical signalling, again emphasising a key role for this hormone in the regulation of plant production in dryland environments. Partial drying of the soil around the roots (PRD) of tomato plants can maintain leaf water potential at values equivalent to well-watered plants for up to 2 weeks (Sobeih et al. 2004). This is largely a function of partial stomatal closure following ABA/pH long distance signalling from roots in drying soil. Ethylene evolution of wild-type (WT) plants increased as soil dried but could be suppressed using transgenic (ACO1AS) plants containing an antisense gene for one isoenzyme of ACC oxidase. Most importantly, ACO1AS plants also showed no inhibition of leaf growth when exposed to partial rootzone drying (PRD) even though both ACO1AS and WT plants showed similar changes in other putative chemical inhibitors of leaf expansion (xylem sap pH and ABA concentration). It seems likely that the enhanced ethylene evolution under PRD is responsible for leaf growth inhibition of WT plants. ACO1AS plants showed no leaf growth inhibition over a range of soil water contents which significantly restricted growth of WT plants.

Rhizosphere bacteria can overcome the ethylene-mediated limitation of pea root and shoot growth during drought Certain bacteria occurring on the root surface and containing the enzyme ACC deaminase degrade the ethylene precursor ACC. Since a dynamic equilibrium of ACC concentration exists between root, rhizosphere and bacterium, bacterial uptake of rhizospheric ACC (for use as a carbon and nitrogen source) decreases root ACC concentration and root ethylene evolution and can increase root growth (Glick et al. 1998, Penrose et al. 2001). To study the effects of modifying root ethylene status on root and shoot growth, pea plants were grown for 10 days at two different soil moisture regimes. Plants were irrigated with either tap water, a naturally occurring rhizosphere bacterium containing the enzyme ACC deaminase and a mutant of this organism lacking ACC deaminase. Only plants grown with the wild-type bacterium showed a promotion of root biomass, leaf area and total biomass, suggesting that these effects were mediated by modifying plant ethylene status, rather than by any other bacterial mechanism. However, it is possible that such effects may not be maintained for a sufficient duration to influence yield, since the long-term influence of soil drought on bacterial colonisation of the root surface has yet to be quantified. Our recent data suggest these fears are unfounded and that bacterial inoculation can stimulate both early vegetative development in drying soil and final seed yield. Signalling between the soil and the plant There is little information on a role for ACC in the soil solution but quite high concentrations of this potential signal have been found, even in well drained soil. The rhizobacteria results suggest that signalling between soil and plant may be an important component of the signalling network that regulates plant performance under stress. Interestingly, both free and conjugated ABA can be taken up by roots and have been detected in the soil solution under a range of crop plants in concentrations up to 10 nM or 30 nM respectively (Hartung et al., 1996; Sauter and Hartung, 2000). The same authors have suggested that soil-sourced ABA participates in maintaining an ABA equilibrium between roots and the external medium and this can be crucial in ensuring that root to shoot ABA signalling operates optimally. Sustaining leaf growth in dryland agriculture has proved to be a particularly intractable problem for plant breeders. We now propose a combination of genetic and agronomical manipulations to exploit soil to root to shoot signalling pathways to sustain leaf growth and biomass production in drying soil.

Applying the water There is considerable pressure on us to develop novel ways to apply more effectively appropriate quantities of water and nutrients to the crop to a) conserve diminishing water supplies and (b) manipulate plant growth in order to increase the profitability and sustainability. We should also address problems of poor uniformity of application of irrigation and try to exploit the opportunites offered by novel understanding of drought stress biology to control growth and water use. We are interesting in evaluating thermal imaging as a means of sensing plant water status and compare this with other means of monitoring and controlling irrigation and in a new project will assess the scope for high precision delivery of water individual plants. Immediate benefits will include improved operation of existing irrigation/fertigation systems while long term benefits include high precision systems capable

of maximum savings of water and nutrients combined with reduced crop wastage and variability. Legislative pressures, and the increasing cost of mains water, make it vital for the industry to increase the efficiency of water use. Furthermore, poor irrigation directly affects profitability by inducing variability within batches of plants which adds to labour costs, particularly for order picking, and crop wastage due to small/poor quality plants. Labour costs may increase by up to 5 times as a result of this variability and manual labour may also be considered as a diminishing resource within the industry. More R and D is needed to achieve substantial and reliable water saving while minimising the risk of potentially catastrophic plant water deficits and crop losses. A variety of novel sensing technologies can be used to assess water requirement, including infra-red thermometers or thermal imaging systems (thermography) which monitor stomatal closure from the resultant rise in leaf temperature (e.g. Jones et al. 1997; Jones 1999). More recently, novel fertiliser treatments, designed to mimic the effect of drought on the plants’ internal signalling systems, have been shown to reduce growth and water use of well watered plants (Davies et al. 2002; Wilkinson and Davies, 2002). Treatments can be delivered via a range of modern water delivery systems that have the potential to deliver precise quantities of water where and when required.

References Bacon MA, Wilkinson S, Davies WJ 1998 Plant Physiology 118, 1507-1515. Ben Haj Salah H, Tardieu F 1997 Plant Physiology 114, 893-900. Davies, W.J., Wilkinson, S. and Loveys, B.R. (2002) New Phytologist 153: 449-460. Davies

WJ, Zhang J 1991 Annual Review of Plant Physiology and Plant Molecular Biology 42, 55-76.

Dodd IC 2003 Journal of Plant Growth Regulation 22, 32-46. Dodd IC, Ngo C, Turnbull CGN, Beveridge CA 2004 Functional Plant Biology 31, 903-911. Else MA, Jackson MB 1998 Australian Journal of Plant Physiology 25, 453-458. Glick BR, Penrose DM, Li JP 1998 Journal of Theoretical Biology 190, 63-68. Gomez-Cadenas A, Tadeo FR, Talon M, Primo-Millo E 1996 Plant Physiology 112, 401-408. Grichko VP, Filby B, Glick BR 2000 Journal of Biotechnology 81, 45-53. Hartung W, Sauter A, Turner NC, Fillery I, Heilmeier H 1996. Plant and Soil 184, 105-110. Hussain A, Black CR, Taylor IB, Roberts JR 2000 Plant, Cell and Environment 23, 1217-

1226. Jones, H.G., Aikman, D. and McBurney, T.A. (1997). Acta Horticulturae 449: 259-266. Jones,

H.G. (1999a) Agricultural and Forest Meteorology 95, 139-149. Jones, H.G. (1999b) Plant, Cell and Environment 22: 1043-1055. Kishor PBK, Hong ZL, Miao GH, Hu CAA, Verma DPS 1995 Plant Physiology 108, 1387-

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Precision, Accuracy and Sense in Measuring Soil Moisture Sayed Azam-Ali Division of Agricultural & Environmental Sciences School of Biosciences University of Nottingham, UK E mail: [email protected] Terrestrial plants depend on solar radiation, carbon dioxide, water and nutrients for their existence. Of these, it is water, or more specifically the availability of soil water, that is the most problematic in terms of its access to plant roots, its measurement by the experimenter or its management by the practitioner. Unlike solar radiation and carbon dioxide, the arrival, distribution, availability and use of water within the root zone of plant communities are not easily linked, conceptually, physically or mathematically. The opacity, variability and structural properties of the soil complicate any attempts at description or prediction of soil moisture distribution and availability in time and space. The behaviour of plant roots both as a result of variations in the soil and the genetic characteristics of the plant species or species growing on it determine the speed and extent of water uptake at the scale of the individual root and the whole system. Nevertheless, knowledge of soil moisture in relation to plant behaviour is important because the dry matter produced by any plant species is linearly and positively correlated with transpired water with a characteristic `transpiration equivalent’ (g kPa kg-1) that is particular to each species (Azam-Ali and Squire, 2002). Any restriction in the supply of water to roots delays the production of dry matter because stomatal closure to restrict transpiration limits the entry of CO2 into leaves. This decrease in growth rate can be calculated in terms of `Lost Time’ i.e. the number of days required for water limited vegetation to `catch up’ with the productivity that would have been achieved without that limitation. Because soil volumetric moisture content (θv) is expressed as a percentage of the total soil volume that is occupied by water, it defines the quantity of water stored in a `bucket’ of soil of known depth. However, in terms of vegetation, the depth of the bucket is not set by the maximum depth of the soil itself but by the maximum depth of roots able to access water. To calculate how much of the volume of water in a soil that plants can reach, we need to measure or estimate the depth and density of the root system. Root systems are genetically complex and grow in an opaque medium that modifies their distribution and activity. Measuring or estimating the size of roots systems is physically and mathematically daunting. In practice, most estimates of root systems in relation to water use and irrigation assume a uniform speed of descent i.e. a root front velocity (cm d-1) to a depth or `zero flux plane’ above which all water is assumed to be lost through evaporation and below which all water is assumed to be lost through drainage. This paper briefly reviews the importance of soil water in relation to the productivity of vegetation in terms of rate of biomass (total dry matter per unit area of ground) and speed (rate of progress to maturity). The concept of a soil water balance is used to partition various components of the hydrological cycle into inputs, outputs and soil storage. The soil storage term S is further refined to define measurements of θv in terms of the total soil volume. Characteristics and assumptions made about the behaviour of roots are considered in relation to size of S and the amount of water that is accessible to plant roots.

Techniques used to estimate θv, include direct (gravimetric) methods, or indirect methods, primarily through neutron scattering (e.g. the neutron probe) or electromagnetic methods that measure the dielectric characteristics of soil (e.g. capacitance probes). Recent concerns about the use of radioactive sources have encouraged the development of dielectric techniques to replace the neutron probe. This paper reviews practical and theoretical issues in relation to the measurement of θv and compares gravimetric, neutron probe and capacitance probe-based estimates of θv. In particular, the limitations of using access tubes for both neutron and dielectric techniques are highlighted in terms of resolution, accuracy and agronomic factors that include variations in plant spacing and arrangement and combinations of species. In particular, problems associated with the insertion of access tubes, the influence of air gaps, stones and soil discontinuities are highlighted. The paper then reconsiders soil moisture release characteristics (i.e. the relation between soil water content and soil water potential, Ψs) as a basis for estimating soil moisture availability. The inadequacies of using θv as a useful indicator of water requirement are discussed and future priorities for assessing water need in terms of when and how much water to provide are briefly introduced. References Azam-Ali SN & Squire GR 2002. Principles of Tropical Agronomy. Wallingford, UK: CAB

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Some Unresolved Issues in Evaporation Relative to Transpiration and in Crop Water Use Efficiency Theodore C. Hsiao Department of Land, Air and Water Resources University of California Davis, USA E mail: [email protected] Most of the water required to grow a crop goes to evapotranspiration (ET), being converted to water vapor through the input of energy, most of which comes directly from solar radiation. ET or consumptive water use is largely beneficial, in that plants produce biomass by assimilating carbon dioxide in exchange for the water transpired. Carbon dioxide assimilation and transpiration (T) are closely linked, and faster assimilation and high production are almost always associated with high crop water use, as long as that use is the result of transpiration. This fact makes it difficult to save water by reducing transpiration. In contrast, soil evaporation is not in exchange for carbon assimilation, and hence, may be considered as non-beneficial use. This is the basis for advocating that soil E be minimized to save water while still maintaining crop productivity. The ratio of E to T is determined mostly by four factors. A key factor is the proportion of soil surface covered by the crop canopy. The fractional canopy cover determines the fraction of solar radiation captured by the canopy, as well as the fraction of radiation reaching the soil surface. Absorbed energy being the dominant source of energy required for evapotranspiration, the ratio of E to T is closely tied to the fractional canopy cover, as long as the crop is well supplied with water and the soil surface is fully wet. E would be reduced as the soil surface dries and its water vapor pressure decreases. T would be reduced if the crop develops water deficit and its stomata close. T and E interact due largely the advective transfer of energy (sensible heat) between the canopy and adjacent soil surface. For efforts to enhance crop water productivity (WP), an important uncertainty is the extent of that advective transfer, which would increase T if E is suppressed. This was assessed in a field experiment in a novel way and the results indicate that T may be increase at the most by a few percent if E is eliminated. Some issues here are: (a) More data on canopy warming due to dry soil surface are needed, to verify the limited data collected so far, and to expand the data to cover more crops and different climatic conditions. (b) We still need more and better methods to measure soil E and plant T separately. To the first approximation, soil E of a crop field of partial canopy cover can be simulated quite well with a simply model based on the fractional canopy cover, reference ET, and with soil E divided into two stages. Stage 1 is when the soil surface is fully wet and E proceeds at the potential rate per unit of exposed soil surface area; and stage 2 starts when the soil surface begins to dry and its water vapor pressure drops below that of free water at the same temperature. Stage 2 evaporation declines with time, with cumulative E being approximately proportion to the square root of time. This model was shown to predict quite well the difference in ET caused by different planting density and canopy cover. Unsettled issues are: (a) How does soil type, particularly texture, affect the parameters for stage 2 evaporation? (B) Is there a more accurate but still simple way to simulate stage 2 drying? (c) How to determine when stage 2 starts, with reasonable accuracy?

One proposal to save water is to minimize the use of sprinklers to apply irrigation water, based on the reasoning that evaporation from the water drops sprayed into the air adds much to the total ET. This overlooks the fact, however, that by humidifying and cooling the air, ET of the crop would be suppressed while under sprinkler irrigation. A way to obtain ET under sprinkler irrigation was worked out using both lysimeters and many well placed catch cans. Although the data are variable from experiment to experiment due to method limitations, the mean result indicate that ET under impulse sprinkling may be only about a half of the ET without sprinkling. The issue here is that data on the rate of evaporation of the water drops while falling through the air are sorely needed calculate the extent water would be saved by not using sprinklers. Regarding transpiration, there are many studies on variations in transpiration of single leaves as affected by changes in stomatal conductance in response to differences in the leaf-to-air water vapor deficit (VPD). The significant of this behavior in determining crop ET has not been adequately assessed in field studies. In an experiment where canopy conductances were measured by micrometeorological means, it was found that for a crop (sweet corn) that does not exhibit stomatal response to VPD, ET of its full canopy was positively correlated with changes in VPD as they occurred with weather changes from day to day, and canopy conductance basically stay the same over much of the season. In contrast, ET of a crop (sunflower) that does exhibit stomatal response to VPD basically did not change with changes in VPD under the same field conditions. This is apparently the result of canopy conductance of sunflower changing in the opposite direction to that of changes in VPD. The results raise the following issues: (a) Kc (crop coefficient) of crops should be adjusted for the stomatal VPD response, but how? (b) How much and for what crop are the slopes of biomass vs. cumulative ET plots (WP) in the literature modulated by stomatal response to VPD? (c) There is a need for much more data on stomatal VPD response of field grown crops and the related data on their ET under different VPD. Also related to stomatal response to humidity is how photosynthetic water use efficiency (abbreviated as WUE, also known as transpiration ratio) is affected by this response. Analyzing with the gas exchange equations for single leaves, it has been shown that the ratio of intercellular CO2 (Ci) to atmospheric CO2 (Ca) is a critical parameter in determining WUE. Whether this conclusion can be applied to canopies without up-scaling is a critical question. In a field study, it was demonstrated that changes in the ratio of Ci/Ca caused by the stomatal response to humidity must be accounted for in order to use the equations to predict WUE of the canopy. This raises the issue of the need for other data for other crops to support this conclusion. In addition, there are some other important issues regarding WP: (a) Ci being so important, carbon isotope discrimination is a very valuable technique to assess WUE, but there are a number of uncertainties regarding that technique. (b) Do deficit irrigation and PRD lower Ci, increase HI, and do they bring about more exhaustive extraction of the soil water? The need is for more quantitative measurements of ET in such studies, not just a measurement of applied water, so that changes in soil water balance are taken into account. (c) Is the normalization for atmospheric CO2 proposed by the FAO WP project adequate? Are there better procedures to normalize?

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