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Van Opstal, J., Droogers, P., Kaune, A., Steduto, P. and Perry. , C. 2021. Guidance on realizing real water savings with crop water productivity interventions. Wageningen, FAO and FutureWater. https://doi.org/10.4060/cb3844en

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Contents

Acknowledgements

Executive summary

Introduction

1.1 Objective

1.2 Audience

1.3 Relevance

2 Background and concepts on real water savings

3 Crop and water management options in irrigated agriculture

3.1 Introduction

3.2 Intervention framework

4 Inventory

4.1 Inventory database structure

4.2 Summary of inventory findings

4.3 Most and least successful interventions

5 Interventions

Conclusions

References

Annex 1. Inventory reference list

Annex 2. Summary results inventory

TABLES

Table 1. Water scarcity response options by major policy domain (FAO, 2012)

Table 2. Overview of the WCT’s (water conservation technologies) discussed in Pérez-Blanco et al. (2020)

Table 3. Categorization of the interventions as used in this guidance document

Table 4. Inventory summary of the number of publications reporting increases or decreases in irrigation, evapotranspiration (ET), crop yield and water productivity (WP) resulting from various field interventions

Table 5. Overview of top five and bottom five interventions for reducing irrigation or water applied, reducing evapotranspiration (ET), increasing crop yield or water productivity (WP-ET) per theme: water management (blue), soil or land management (yellow) and agronomy (green).

Table 6. Inventory summary with average reported changes (%) in irrigation (I), evapotranspiration (ET), crop yield (Y), water productivity (WP), and irrigation water productivity (I-WP) for various field interventions

FIGURES

Figure 1. Last century perspectives on water losses. Irrigation water losses in canals (left) and irrigation water losses in the field (right) to groundwater or surface runoff. Source: FAO (1989a, 1989b)

Figure 2. Variations in the water productivity of wheat (kg/ha/ET) in different regions.

Figure 3. Water accounting framework for irrigated agriculture.

Figure 4. Simplified water accounting system known as follow the water, with dS representing delta (i.e. change) of water stored

BOXES

Box 1. ‘Follow the Water’ Terminology

Box 2. Does increased water productivity save water?

Box 3. From reported water savings to practical implementation

Acknowledgements

This report was prepared by Jonna van Opstal, Peter Droogers, and Alexander Kaune, from FutureWater, in collaboration with Pasquale Steduto and Chris Perry, independent consultants subcontracted by FutureWater.

The authors wish to acknowledge the contribution from Louise Whiting, FAO Land and Water Officer, and Hugh Turral, FAO Consultant, whose valuable inputs were integral to the production of this report. English editing and proof reading was done by Ruth Raymond. Publishing arrangements and graphic design were carried out by Jim Morgan.

Funding for the development of this publication was received from the FAO Regional office for Asia and the Pacific as part of the Regional Water Scarcity Program.

Executive summary

This technical document contains clear and practical guidelines on how to implement ‘real’ water savings in agriculture through interventions for enhancing crop water productivity. A distinction is made between real water savings and ‘apparent’ water savings. Apparent water savings record reductions in water withdrawals but do not account for changes in water consumption. Real water savings record reductions in water consumption and non-recoverable return flows (runoff or percolation). This guidance document emphasizes the paradox of water savings at field and basin scales, which usually do not translate into increased water availability for other users as is commonly believed.

An intervention framework groups water savings interventions into three categories: water management; soil and land management; and agronomy. An inventory of publications lists information on each intervention in terms of changes of the application of irrigation water, water consumption (i.e. evapotranspiration), crop yield, and water productivity. The best interventions for achieving higher water productivity mostly relate to agronomic practices. Reductions in water consumption (evapotranspiration) are achieved through selected agronomic and water management practices.

Realizing real water savings is context-specific. This guidance document provides information on the expected changes at field scale resulting from various interventions. The impact in a larger context requires analysis at district level or basin scale. The ‘follow the water’ concept introduces water accounting terms to communicate the categories of water flows in a system. ‘Water saved,’ for example, is the amount of water resulting from reducing consumption and/or the non-recoverable fraction of the return flows that can be made available for alternative uses. Following the concepts and guidelines in this document, decision-makers can improve the management of their water systems by introducing sustainable interventions to achieve real water savings.

1. Introduction

1.1 OBJECTIVE

This report aims to provide clear and practical guidelines on how to implement ‘real’ water savings in agriculture by selecting suitable interventions that enhance crop water productivity. A distinction is made between real water savings and ‘apparent’ water savings. Apparent water savings record reduced water withdrawals but do not account for changes in water consumption; this is commonly used as the definition for water saved through interventions. Real water savings record reductions in water consumption and non-recoverable return flows (runoff or percolation).

This report emphasizes the paradox of water savings at field and basin scales, which usually do not translate into increased water availability for other users. It offers water savings options that can help agriculture become more productive without increasing water consumption. The background and concepts are explained in Chapter 2. Crop and water management interventions are described in Chapter 3, including an intervention framework. Chapter 4 provides a summary of the inventory reference database, including the impact of water savings interventions on water consumption and crop production. Chapter 5 provides detailed descriptions of the various water savings interventions.

1.2 AUDIENCE

This guidance document targets audiences ranging from extension services officers to water managers and irrigation specialists, who design and manage irrigation systems, and policymakers or river basin planners, who make decisions on the allocation of water resources.

1.3 RELEVANCE

Increased water use has led to water scarcity in many Asian countries. This trend will continue: the gap between water demand and supply is projected to increase due to population growth and economic development (Dinar et al., 2019) as well as environmental factors, such as land degradation (IPCC, 2019) and climate change (Turral et al., 2011). Efforts to reverse these trends should focus on irrigated agriculture, since irrigation is the largest consumer of freshwater withdrawals in almost all water-scarce regions. The Food and Agriculture Organization of the United Nations (FAO) has played a leading role in finding agricultural solutions to managing water shortages.

Unfortunately, overcoming the water crisis through agricultural interventions is not simple and has often led to unrealistic expectations. Recent decades attention has been brought to the misconceptions and overly simplistic (and often erroneous) views in agricultural water management. However, the uptake of these warnings by decision-makers and the irrigation sector has been limited for various reasons. For example, decision-makers rarely have sufficient information on which to base their determinations. The availability of measured observations on real water savings requires extensive data collection. Frequently, the interest of key players is bound to certain scales i.e. the field scale for farmers and basin scale for river authorities. This could make it difficult to find a common goal and language. A significant issue is that the modernization of irrigation systems has, in many cases, increased water consumption, rather than create the water savings that are often assumed to be delivered by irrigation modernization programmes (Adamson and Loch, 2014; Pérez-Blanco et al., 2020; Perry and Steduto, 2017; Ward and Pulido-Velazquez, 2008) Concepts such as irrigation in the basin context and water accounting have shown that water savings at the basin scale are in reality often limited and that water consumption may even increase (Giordano et al., 2017)(Giordano et al., 2017).

FAO’s Regional office Asia and Pacific (RAP) Water Scarcity Programme aims to develop a suite of tools, guidance documents and policy dialogue processes to assist countries to improve water productivity in the face of scarcity and to prepare the agriculture sector for a productive future with less water. The proposed approach is appropriate in that it deliberately and systematically combines technical and data analysis with policy and governance reform and capacity development, the latter being a difficult task that generally receives less attention and investment.

2. Background and concepts on real water savings

It is commonly perceived that large quantities of water are wasted during the irrigation process and that real water savings could reduce the need for facilities to extract more water (Molden et al., 2001). This perception is derived from common knowledge that on-farm irrigation efficiencies are often in the order of 20 to 50 percent, implying that the remaining 80 to 50 percent of the water withdrawn is somehow lost. Typical examples of this thinking have been reflected in various FAO publications over the past 30 years (see Figure 1).

The chief misconception stems from the classical notion of ‘irrigation efficiency’ as developed in irrigation engineering. Irrigation efficiency is commonly measured as the ratio of water consumed to water applied or withdrawn from a source. But applying this concept to water basins could lead to incorrect decisions and therefore to faulty public policy (Keller and Keller, 1995). The authors observe:

“This classical efficiency concepts do not account for return flows and their subsequent reuse. Thus, applying irrigation efficiency concepts alone could lead to the conclusion that significant opportunities existed for efficiency gains. In reality, however, despite local irrigation inefficiencies, the scope for improved efficiency at the sub-basin or basin scale (and thus for real water savings) is limited due to the reuse of the return flows elsewhere. Moreover, because of the opportunity to recharge groundwater aquifers through return flows, a strategy involving overwatering on the fields and allowing seepage losses from conveyance canals may be preferable to promoting local (application or conveyance) efficiency gains.”

The scientific interest in real water savings is growing rapidly and, along with it, the quantity of journal articles, expert reports and conferences. The term ‘real water savings’ emphasizes the need to broaden our perspective from the field to the entire basin. In other words, we need to understand real water savings as an intervention that releases an identified quantity of water to an alternative use. A recent review (Pérez-Blanco et al., 2020) observed that the number of case studies on the performance of water conservation technologies beyond the field scale has increased significantly in recent years: out of 224 applied case studies on this topic over a period of 42 years (1976-2017), some 91 (40.6 percent) were published in the last nine years (2010-2018). -

Box 1 defines the key concepts used in this publication.

The siloed worlds of the water and agriculture/agronomy sectors have contributed to the misconceptions around irrigation and water wastage. Further integrating the two sectors could potentially lead to real water savings and/or increased water productivity. Typical examples of the interface between water management and agronomical practice, where potential water productivity improvements can be made, are mulching, deficit irrigation at specific times, planting density, weed control, fertilizer, cultivar selection, growth enhancers (polyamines: putrescine, spermidine), tillage practices and terracing, among others.

A second important aspect of water savings is the relationship between crop evapotranspiration and yield. It is reported that yield is linear in relation to crop transpiration under the conditional constraint of “everything else being equal (Perry and Steduto, 2017).” Many options for real water savings exist, particularly in Asia with its wide diversity of irrigation practices, crops and crop management approaches.

According to Perry and Steduto (2017):

“When field data are collected from a large number of farmers, some farmers achieve substantially higher yields for the same level of crop transpiration than other farmers. A common interpretation of this observation is that better management of water and other agronomic inputs/practices could capture this increment and overall production could be raised for the same level of water consumption (or water could be ‘saved’ while production is maintained).”

The authors note that the near linear relationship between yield and crop transpiration is “derived for a specified and consistent package of crop husbandry (planting date, cultivar, planting density, fertilization status, soil, etc.) with only water input being varied.” In other words, if water is limited, simply increasing the supply will increase production (kg) but will not increase productivity (kg/m^3). Productivity increases (which provide the basis for real water savings) will usually depend on changes to other aspects of the farmer’s practices that focus on the water-agronomy aspects where real water savings are possible or where higher production can be achieved with the same amount of evapotranspiration.

Non-linearity between crop evapotranspiration and yield can be substantial, however, given the wide-range of climate, agro-economic zone and farm management practices.

Figure 2 shows that ranges in yields can differ by a factor of five with the same amount of evapotranspiration. Box 2 elaborates further on the connection between water savings interventions and water productivity.

In addition to the paradigm shift in agricultural water management from a local irrigation efficiency perspective to basin scale assessments, water saving is another important consideration. It may seem obvious that water saving is generally considered positive, but what happens to the saved water and at which scales (temporal and spatial) should the saving be assessed?

Perry (2020, personal communication) proposes the following definition for water saving:

“Water saving is an intervention that results in incremental water being made available for an alternative beneficial use, including but not limited to environmental services or stabilizing an aquifer.”

In other words, if there is no alternative beneficial use, actions to save water are probably not needed. One could add to Perry’s definition that the alternative beneficial use should have a higher priority and/or higher water productivity than the original use. Priority is often determined by decision-making processes allocating water for different sectors (e.g. agriculture versus environment), while water productivity is generally used to compare use within one sector (e.g. irrigated vegetables versus irrigated rice). Extensive research and literature are available on water productivity (expressed as kg per cubic meter water consumption, or USD per cubic metre water consumption).

Moving from an on-farm to a basin perspective, it is often found that because ‘lost’ water is often reused, far less water is lost than commonly perceived. From a hydrology perspective, this is common knowledge and is referred to as the water cycle: water is never lost because evaporated water will precipitate elsewhere as rain or snow. In irrigation science, this concept started around 2000. It is often referred to as water accounting, which focuses on withdrawal and return flows within a basin context. A typical example of this approach is shown in Figure 3.

Many efforts have been made to improve and enhance water accounting frameworks. These efforts have introduced refinements that add an additional level of complexity but often lack the data needed to make them useful. Moreover, the complexity of the frameworks has made it difficult for decision-makers and non-specialists to grasp the main message: water is never lost. Following internal discussions, the International Commission on Irrigation and Drainage adopted a simplified approach focusing on four main components of water flows. This simplified approach was summarized by Perry (2007) to ensure that focus would be on the main components of those water flows. Our report uses this approach – known as ‘follow the water’ – which is outlined in Figure 4. The main concept is that water diverted to irrigation schemes can be divided into the following components:

•The consumed fraction (essentially evapotranspiration), comprising:

–beneficial consumption (for the purpose intended or another beneficial use);

–non-beneficial consumption (such as by weeds, evaporation from wetted surfaces, or capillary rise during a fallow period);

•The non-consumed fraction, comprising:

–recoverable flows (water flowing to drains and back into the river system for possible diversion downstream, and percolation to freshwater aquifers);

–non-recoverable flows (percolation to saline aquifers, outflow to drains that have no downstream diversions or direct outflow to the ocean).

The inventory of water savings techniques described in Chapter 4 and the guidelines for practical intervention in Chapter 3 are based on the follow the water approach.

3. Crop and water management options in irrigated agriculture

3.1 INTRODUCTION

The necessity to improve crop and water management has been highlighted in many studies and reports. However, most of these limit themselves to emphasizing the importance of optimizing crop and water management without actually providing guidelines on how to do so. Indeed, the scientific literature includes many detailed studies on rather small and location-specific components of optimizing crop and water management. Another challenge is to develop a structured framework that allows broader options to be broken down into smaller ones. No universal categorization of interventions exists as this depends on the overall objective. A number of options relevant to crop and water management are summarized below.

FAO 36

An FAO study on adaptation to climate change (Turral et al., 2011) includes an interesting framework for improving crop and water management.

The framework consists of the following elements:

• On-farm management

– crop selection and crop calendar

– farm and crop management – fertilizer management

– water management on farm

– irrigation technologies on farm

– depletion accounting

– flood protection and erosion

– commercial agriculture.

• Adaptation at irrigation system level

– water allocation

– system performance

– cropping patterns and calendars

– conjunctive use of surface water and groundwater

– irrigation policy measures.

• Adaptation at river basin and national levels

– irrigation sector policy

– coping with droughts

– coping with flooding – structural and non-structural interventions

– managing aquifer recharge

– assessment of adaptation options to ensure irrigation supply security.

• Adaptive capacity in agricultural water management – policies, institutions and the structure of the subsector

– mechanisms for allocation

– national food policy issues.

• Institutions

• Long-term investment implications for agricultural water management

The report concludes that, for irrigated agriculture specifically, the options at farm level can be considered in the following terms:

1. manipulation of crop selection and the cropping calendar;

2. better management of factor inputs – nitrogen and agricultural chemicals;

3. improved water management technologies and techniques for cropping.

Aerts and Droogers, 2004

Similarly, Aerts and Droogers (2004)until now clear guidance on how to respond to this challenge, particularly at the river basin level, has been lacking.This book has been developed from the ADAPT project, focusing on the development of regional adaptation strategies for water, food and the environment in river basins across the world. A generic methodology is presented and applied to seven case studies in contrasting geographical areas of the world: Mekong (SE Asia report that two main groups of options at the farm level should focus on:

1. improved farm management;

2. crop production technology.

FAO 38

An FAO report, Coping with water scarcity: an action framework for agriculture and food security (FAO, 2012) made it very clear that changes are needed in water policy concerning:

• Managing supply

– increased storage

– groundwater development

– recycling and re-use

– pollution control

– inter-basin transfer

– desalination.

• Managing demand

– re-allocation

– increased efficiency of use.

In terms of agricultural policy, the report described the following options:

• supply enhancement

• water recycling and re-use in irrigation

• reducing water losses[1]

• improving crop water productivity

• re-allocating water from lower to higher-value use in irrigation.

Perry et al., 2009

The landmark[2] paper by Perry, Steduto, Allen and Burt is concerned with increasing productivity in irrigated agriculture. Although the study focuses mainly on putting the terminology and thinking about water savings into a proper perspective, it also discusses the crop and water management options that are available to farmers. The paper argues that there is no simple answer to the question of which irrigation method is best. Moreover, the authors emphasize that “irrigation technology is often a farm-level choice, and it is appropriate to consider the farmer’s perspective carefully in understanding options and impacts (Perry et al., 2009).” The choices made by farmers depend on:

• Increased income. Farmers will have an incentive to improve if yield quantity, quality, or alternative high-value crops will more than adequately reward the investment.

• Risk aversion/food security. Farmers may shift from rainfed agriculture to irrigation to reduce the uncertainties associated with variable rainfall patterns. Similarly, they may shift from public surface water delivery systems to well water because surface water is delivered in an inflexible and unreliable manner.

• Convenience. This is primarily seen in commercial farming. For example, a farmer may not want to have to wake up in the middle of the night to receive water deliveries or he may be able to deliver fertilizers more precisely and cheaply through ‘fertigation’[3] systems.

• Reduced costs. A farmer may save on pumping costs if delivery losses are reduced; he may save on labour by installing equipment that does not require a constant field presence.

• Non-water related motivations. These include saving on labour, growing higher-value crops, reducing uncertainty, cost, credit availability, extension advice, technical support and land levelling, among others.

The Asia Pacific Adaptation Network (APAN)[4]

APAN has developed an Adaptation Technology Database that defines ten categories, each of which has a subset of technologies. Relevant categories are:

• capacity building and stakeholder organization

• crop improvement

• cropping techniques

• erosion control

• processing techniques

• soil management

• storage options

• sustainable crop management

• urban agriculture.

The total number of technologies is limited and it is unlikely that the database is still current (the last update was in 2015). The approach is quite interesting, however, as each of the technologies has the following descriptors:

• technological maturity

• applicable immediately

• technology owners

• cost

• ease of maintenance

• technology performance

• co-benefits,

• suitability for developing countries.

The Asian Development Bank (ADB), 2020

A so-called ‘good practice guide’ for supporting adaptation decision-making for climate-resilient investments in the water sector (Droogers and Carpenter, 2020) includes some interesting criteria for evaluating various adaptations. Although the criteria are specifically focused on climate change adaptations, some are relevant to our purposes:

• Time – implementation period and longevity of intervention

– short, medium, long

• Effectiveness – extent to which vulnerability is reduced

– contributes, partial, total

• Relative cost – compared to other options or business-as-usual

– low, medium, high

• Co-benefits – beyond resilience e.g. carbon sequestration, job creation

– limited, medium, high

• Barriers to implementation – degree of complexity, e.g. multi-country agreements

– easy, medium, difficult

• Capacity required to implement – extent of specific e.g. technical, legal, data requirements

– simple, medium, advanced

• Scale of implementation – areal extent of benefit from adaptation measure

– local, regional, national, international

• Applicable locations and conditions – extent of geographical limitations

– specific, many, universal

Pérez-Blanco et al., 2020

This study examined 230 empirical and theoretical papers on water conservation technologies (WCTs). The review concluded that WCTs should not be regarded as simply a way to achieve water conservation, but also as a means to stabilize and enhance agricultural water productivity and farmers’ income where water is scarce.

The study makes a strong distinction between WCTs and WCPs (water conservation policies) and argues that if the goal is water conservation (real water savings) to effectively increase the quantity of water available for other uses, appropriate policies are an essential complement to new technologies.

In preparing this guidance document, the 230 interventions reported by Pérez-Blanco et al. were further examined, filtered and categorized (Table 2). Many of the technologies had an objective to achieve ‘increased efficiency’ as a means of saving water, but in most cases, this related only to field-scale level reductions in water applications.

Interestingly, this study hardly addresses agronomic aspects of WCTs and is limited to two categories of interventions: ‘alternate wetting and drying’ and ‘deficit irrigation.’ Perry and Steduto (2017) explain the importance of including agronomy technologies in such reviews:

• When field data are collected from a large number of farmers, some farmers achieve substantially higher yields for the same level of crop transpiration than other farmers.

• A common interpretation of this observation is that better management of water and other agronomic inputs/practices could capture this increment and overall production could be raised for the same level of water consumption (or water could be ‘saved’ while production is maintained).

• The near linear relationship between yield and crop transpiration is derived for a specified and consistent package of crop husbandry (planting date, cultivar, planting density, fertilization status, soil, etc.) with only the water input being varied.

IWMI Research Report 169

The International Water Management Institute (IWMI) initiated a rethinking of irrigation water efficiencies: “The new era of water resources management: From ‘dry’ to ‘wet’ water savings.’” IWMI Research Report 169 (Giordano et al., 2017) outlines several key ideas that fundamentally changed the research paradigm from a focus on irrigation efficiency and the performance of irrigation systems to one centred on water productivity and river basin management.

The report describes a framework for achieving real water savings. It defines four main intervention groups, providing examples for each:

• Increase yield per unit of water consumed by, for example:

– improving water management by better timing water supplies to reduce stress at critical crop growth stages or by increasing the reliability of supplies to enable farmers to invest more in other agricultural inputs;

– improving non-water inputs that increase production per unit of water consumed, and agronomic practices, such as laser land levelling and fertilization; and

– changing to new or different crop varieties with higher yield per unit of water consumed.

• Reduce non-beneficial depletion by, for example:

– increasing the proportion of water applied that is used beneficially by crops, by: i) reducing evaporation from water applied to irrigated fields through more capital intensive technologies (such as drip irrigation) or better agronomic practices (such as mulching or changing crop planting dates to match periods of less evaporative demand); and ii) restricting evaporation from bare soil through conservation agriculture (such as land levelling or zero tillage);

– lessening evapotranspiration from fallow land by reducing the area of free water surfaces, decreasing non-beneficial or less beneficial vegetation, and controlling weeds;

– reducing water flows to sinks by decreasing irrecoverable deep percolation and surface runoff by such measures as canal lining and precision irrigation;

– minimizing salinization (or pollution) of recoverable return flows by minimizing flows through saline (or polluted) soils and groundwater; and

– shunting polluted water to sinks to avoid the need for dilution with water of usable quality.

• Tap uncommitted flows by, for example:

– adding water storage facilities, including reservoirs, groundwater aquifers, tanks and ponds, on farmers’ fields;

– improving management of existing facilities to obtain more beneficial use of existing water supplies; and

– reusing uncommitted return flows through gravity or pump diversions to increase irrigated area.

• Reallocate water among uses by, for example:

– reallocating water from lower to higher-value uses within or between sectors while addressing possible effects on downstream uses.

3.2 INTERVENTION FRAMEWORK

The frameworks described in the previous section have been used to derive a practical hierarchal setup for the interventions described in this guidance note. The setup is simple and consists of three levels: theme, category and intervention. Each intervention has the potential to enhance crop and water management. The term ‘enhance’ is used here because the overall aim is to increase water productivity at the basin scale and/or to reduce water consumption to support downstream water users.

The interventions described in this guidance note go beyond the traditional water/ irrigation perspective, as it is clear that real water savings can more often be found in agronomy interventions rather than in water/irrigation interventions only.

Interventions for integrated or diversified farming systems are excluded from this framework. Examples of such systems are farms that integrate crop production with livestock and thus improve their economic productivity per unit land.

1 The report emphasizes that it is now widely accepted that, while irrigation losses appear high, a large part of these ‘losses’ are return flows or aquifer recharge, which can be tapped by other users further downstream.

2 152 citations according to Science Direct (December 2019)

3 Fertigation is the practice of injecting fertilizers in the irrigation water.

4 http://www.asiapacificadapt.net/adaptation-technologies/database

4. Inventory

The intervention framework presented in Section 3.2 of this document (Table 3) provides a structure for three themes – water, soil/land and agronomy – and the categories and interventions underlying each theme. Based on this framework, we conducted an inventory to quantify the impact of each intervention on water management and productivity. A literature review gathered results from peer-reviewed articles, technical documents and other publications. This chapter provides a summary of the inventory and our main findings.

4.1 INVENTORY DATABASE STRUCTURE

The list of references included in the inventory is provided in Annex 1. The inventory is based on the following structure.

Publication type

The literature used for compiling the inventory database consisted of peer-reviewed articles, technical documents and reports, working papers and conference papers.

Countries and climate zones

The literature review focused on countries in the Asia and Pacific region. Other countries were included whose climatic conditions are similar to those in the region, for example the Mediterranean and the western United States of America. Distinction was made between arid, temperate, tropical and continental climates, according to the Köppen climate classification.

Methodology

The methods and spatial scale applied in each study were noted (if reported). These varied from field experiments, farmers surveys, measurements of a block of fields and irrigation district (scheme) level, and simulation models at field, district and hydrological levels.

Reported changes

Publications were included that could indicate a change in water volume or crop production due to a particular intervention. These changes were quantified as percentages of change from the original condition (baseline). Changes were noted for the following aspects:

• irrigation or water applied;

• evapotranspiration or water consumption;

• return flow as runoff or drainage;

• crop yield;

• water productivity: yield per unit of evapotranspiration (water consumed);

• irrigation water productivity: yield per unit of irrigation (water applied).

4.2 SUMMARY OF INVENTORY FINDINGS

A summary of the inventory and reported changes is presented in Annex 2, indicating the average changes in percentages for the various interventions presented in 240 publications. These are also listed in Table 4, which indicates the number of publications reporting increases or decreases for irrigation, evapotranspiration (ET), crop yield and water productivity.

The publications reporting changes in irrigation fall mostly under the water theme. The studies examining the impact of drip irrigation report that the amount of irrigation water applied decreased in all cases. For evapotranspiration, more studies reported an increase in irrigation water than reported a decrease. Ultimately, crop yield increased in almost all studies of drip irrigation that included such information. As shown in Table 4, all of the studies show that regulated deficit irrigation caused ET to decrease. However, yield also decreased in almost all of the studies reporting on these aspects. Zero tillage and mulching are comparable interventions that use plant residue or other material to cover the bare soil. Both interventions promote a decrease in evapotranspiration and an increase in yield. These interventions also successfully increased water productivity. Water productivity also increased with the use of fertilizers. Other interventions are listed in Table 4 and are also summarized in Annex 2.

4.3 MOST AND LEAST SUCCESSFUL INTERVENTIONS

Table 5 lists the five most successful and the five least successful interventions for each irrigation, evapotranspiration, yield and water productivity. The anticipated success rate is independent of other factors, e.g. number of studies, crop type, irrigation method, climate zone and country, but is based on the average of all studies, as listed in Annex 2, excluding interventions with two or fewer publications in the inventory.

The top five interventions for reducing irrigation are all related to water management (in blue). Notably, regulated deficit irrigation results in a reduction in irrigation as well as evapotranspiration. However, deficit irrigation falls into the bottom five for crop yield and water productivity. The best interventions for achieving higher water productivity are mostly related to agronomic practices. Increases in yield can be achieved through both agronomic practices and water management interventions, namely subsurface irrigation and conversion to pipe irrigation distribution systems, rather than open canals. It should be noted that the pipe distribution system is an intervention implemented at a district (or subunit) level. This requires more investment and cooperation from farmers but can result in higher returns in crop yield. Crop rotation is one of the top five interventions for reducing evapotranspiration. However, it falls into the bottom five for both yield and water productivity. By changing the crop rotation, fewer crops are grown, which has a larger impact on yield than on reducing evapotranspiration, as indicated by water productivity.

The conclusion is that there are a range of management options that farmers can choose to improve their water productivity while protecting their incomes. Chapter 5 provides further detail on each intervention, including its to a particular spatial scale. The chapter also supplies practical guidance on implementing the interventions. Box 3 highlights the perspectives of decision-makers and possible incentives for farmers to implement specific interventions.

5. Interventions

This chapter provides guidelines on various crop water productivity interventions, including background, details on implementation, suitability and potential impact at the field scale, and basin-scale water issues. Since interventions must always be location-specific with regard to climate, socio-economic context, political preferences, governance mechanisms, etc., they should be considered as options for consideration rather than rigid guidelines.

The interventions are based on the framework defined in Chapter 3. Chapter 4 described the actual range of interventions. This chapter adds a mix of scientific literature, reports, websites and experiences to further characterize the interventions. Expert knowledge has been used to combine these sources and exact referencing has not been possible.

The interventions are grouped under the following themes: water management, soil and land management, and agronomy. An indication is provided for each intervention if the beneficial water consumption, non-beneficial water consumption, and return flow (concepts explained in Box 1) are expected to be higher or lower compared to a scenario without the intervention.

Conclusions

Achieving real water savings is complex and context-specific. This study provides information on the field-scale changes that might result from various interventions. The impact in a larger context will require analysis at district level or basin scale. The ‘follow the water’ concept introduces water accounting terms to communicate the categories of water flows in a system. Using the concepts and guidelines provided in this document, decision-makers can improve the management of water systems with sustainable interventions that accomplish real water savings.

The inventory provided in this report lists interventions that can lead to increases in water productivity and reductions in water consumption. Several interventions, mainly related to water management and irrigation, are commonly promoted as water savings technologies but the ‘follow the water’ approach indicates that reductions in water consumption are limited. Saving water is solely achieved by reducing water consumption and non-recoverable return flows.

Tools will be needed to translate the approach into practice and assist decision-makers to adopt the approach proposed in this guidance note. This guidance offers relevant information to assist decision-makers and translate field-scale interventions to a basin scale context. It requires a wider audience to continue this work and promote sustainable implementation of water productivity interventions.

References

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Aerts, J.C.J.H. & Droogers, P. 2004. Climate change in contrasting river basins: adaptation strategies for water for food and water for the environment. 288 pp. Wallingford UK, CABI.

Dinar, A., Tieu, A. & Huynh, H. 2019. Water scarcity impacts on global food production. Global Food Security, 23, 212–226. https://doi.org/10.1016/j.gfs.2019.07.007.

Droogers, P. & Carpenter, C. 2020. Supporting adaptation decision-making for climate-resilient investments: good practice guide. Mandaluyong, Philippines, Asian Development Bank.

Food and Agriculture Organization of the United Nations (FAO). 1989a. Irrigation water management: irrigation scheduling. Rome.

FAO.1989b. Irrigation water management: irrigation methods. Rome.

FAO. 2011. The State of the World’s Land and Water Resources for Food and Agriculture. Rome, FAO; London, Earthscan.

FAO. 2012. Coping with water scarcity: an action framework for agriculture and food security. FAO Water Reports 38. Rome.

Giordano, M., Turral, H., Scheierling, S., Treguer, D. & McCornick, P. 2017. Beyond ‘more crop per drop’: evolving thinking on agricultural water productivity. IWMI Research Report 169. Colombo, Sri Lanka, International Water Management Institute (IWMI); Washington, DC, World Bank. https://doi.org/10.5337/2017.202

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Pérez-Blanco, C., Hrast-Essenfelder, A. & Perry, C. 2020. Irrigation technology and water conservation : from panaceas to actual solutions. (submitted)

Perry, C. 2007. Efficient irrigation; inefficient communication; flawed recommendations. Irrigation and Drainage, 56, 367–378. https://doi.org/10.1002/ird.323.

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Perry, C., Steduto, P., Allen, R.G. & Burt, C.M. 2009. Increasing productivity in irrigated agriculture: agronomic constraints and hydrological realities. Agricultural Water Management, 96, 1517–1524. https://doi.org/10.1016/j.agwat.2009.05.005

Turral, H., Burke, J. & Faures, J-M. 2011. Climate change, water and food security. FAO Water Reports 36, FAO Water Reports 36. Rome.

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Annex 1. Inventory reference list

Annex 2.
Summary results inventory

The following table presents the average change in irrigation, evapotranspiration, crop yield, water productivity and irrigation water productivity resulting from each intervention. The number of studies used to compute the average is indicated in the ‘count’ column. Interventions cited by two or fewer publications are excluded from the table. A total of 240 studies were used for this study: 131 in the category of water management; 40 in the category of soil and land management, 54 in the category of agronomy and 15 other interventions that were not included in the intervention framework (irrigation scheduling, raised beds, etc.).

For the first two aspects, irrigation and evapotranspiration, reductions are indicated as negative values and are coloured green. These are perceived as desirable; however, a water accounting context (as described in Chapter 2) is required to determine whether real water savings are achieved. Increases in crop yield, water productivity (per unit of ET) and irrigation productivity (per unit of irrigation) are also in green.

FAO TECHNICAL PAPERS

FAO WATER REPORTS

1 Prevention of water pollution by agriculture and related activities, 1993 (E/S)

2 Irrigation water delivery models, 1994 (E)

3 Water harvesting for improved agricultural production, 1994 (E)

4 Use of remote sensing techniques in irrigation and drainage, 1995 (E)

5 Irrigation management transfer, 1995 (E)

6 Methodology for water policy review and reform, 1995 (E)

7 Irrigation in Africa in figures/L’irrigation en Afrique en chiffres, 1995 (E/F)

8 Irrigation scheduling: from theory to practice,1996 (E)

9 Irrigation in the Near East Region in figures, 1997 (E)

10 Quality control of wastewater for irrigated crop production, 1997 (E)

11 Seawater intrusion in coastal aquifers – Guide lines for study, monitoring and control, 1997 (E)

12 Modernization of irrigation schemes: past experiences and future options, 1997 (E)

13 Management of agricultural drainage water quality, 1997 (E)

14 Irrigation technology transfer in support of food security, 1997 (E)

15 Irrigation in the countries of the former Soviet Union in figures, 1997 (E) (also published as RAP Publication 1997/22)

16 Télédétection et ressources en eau/Remote sensing and water resources, 1997 (F/E)

17 Institutional and technical options in the development and management of small-scale irrigation, 1998 (E)

18 Irrigation in Asia in figures, 1999 (E)

19 Modern water control and management practices in irrigation – Impact on performance, 1999 (E)

20 El riego en América Latina y el Caribe en cifras/Irrigation in Latin America and the Caribbean in figures, 2000 (S/E)

21 Water quality management and control of water pollution, 2000 (E)

22 Deficit irrigation practices, 2002 (E)

23 Review of world water resources by country, 2003 (E)

24 Rethinking the approach to groundwater and food security, 2003 (E)

25 Groundwater management: the search for practical approaches, 2003 (E)

26 Capacity development in irrigation and drainage. Issues, challenges and the way ahead, 2004 (E)

27 Economic valuation of water resources: from the sectoral to a functional perspective of natural resources management, 2004 (E)

28 Water charging in irrigated agriculture – An analysis of international experience, 2004 (E) efforts and results, 2007 (E)

29 Irrigation in Africa in figures – AQUASTAT survey – 2005, 2005 (E/F)

30 Stakeholder-oriented valuation to support water resources management processes – Confronting concepts with local practice, 2006 (E)

31 Demand for products of irrigated agriculture in sub-Saharan Africa, 2006 (E)

32 Irrigation management transfer – Worldwide, 2008 (E/S)

33 Scoping agriculture–wetland interactions – Towards a sustainable multiple-response strategy, 2008 (E)

34 Irrigation in the Middle East region in figures – AQUASTAT Survey – 2008, 2009 (Ar/E)

35 The Wealth of Waste: The economics of wastewater use in agriculture, 2010 (E)

36 Climate change, water and food security (E)

37 Irrigation in Southern and Eastern Asia in figures – AQUASTAT Survey – 2011 (E)

38 Coping with water scarcity - An action framework for agriculture and food security (E/F)

39 Irrigation in Central Asia in figures (E)

40 Guidelines to control water pollution from agriculture in China Decoupling water pollution from agricultural production (E)

41 Yield gap analysis of field crops: Methods and case studies (E)

42 Drought characteristics and management in the Caribbean (E)

43 Water accounting and auditing: A sourcebook (E, F)

44 Drought characteristics and management in Central Asia and Turkey (E)

45 Drought characteristics and management in North Africa and the Near East (E)

46 Guidance on realizing real water savings with crop water productivity interventions (E)

Availability: February 2021

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