Assessing On-Farm Water-Use Efficiency: A New Approach

Transcription

1 Assessing On-Farm Water-Use Efficiency: A New Approach Methodology and Six Case Studies A report on collaborative research undertaken by: The International Center for Agricultural Research in the Dry Areas (ICARDA) and The United Nations Economic and Social Commission for Western Asia (ESCWA) Kamil Shideed Theib Y. Oweis Mohammed Gabr Mohammad Osman ICARDA International Center for Agricultural Research in the Dry Areas

2 All rights reserved International Center for Agricultural Research in the Dry Areas (ICARDA) ICARDA encourages fair use of this material. Proper citation is requested The Authors Kamil Shideed and Theib Oweis are Senior Agricultural and Natural Resource Economist and Senior Water Management Scientist, respectively, at ICARDA, Aleppo, Syria; Mohammed Gabr is a fbrmer Senior Economist at ESCWA; Mohanrmad Osman is a Senior Economist at ESCWA. Recommended Citation Shideed, Kamel; Theib Oweis, Mohammed Gabr, and Mohammad Osman Assessing On-Farm Water-Use Efficiency: A New Approach. ICARDA, Aleppo, Syria, 86 pp. ISBN: X Key Words: Water-use efficiency, water productivity, on-farm water allocation, variable input model, fixed-allocatable input model, supplemental irrigation Cover: Relationship between water-use efficiency and yield for wheat grain in a Mediterranean environment. Source: Zhang and Oweis (1999). ICARDA P.O. Box 5466, Aleppo, Syria Tel.: (+963) (21) , ,225112, Fax.: (+963) (21) , , icarda(ujcgiar.org Web Site:

3 Foreword The increasing scarcity of water for agricultural production around the world is a major cause for concern. The situation is particularly worrying in West Asia and North Africa (WANA) where the per capita share of water in many countries has fallen below the water poverty level. With the rapid growth of the population and the consequent rise in demand for water, water shortages will be an even greater concern in coming years. Currently, agriculture consumes over 75% of the water in the dry areas but this share is projected to drop drastically and may reach 50% in some countries of WANA over the coming 25 years. The food security of the poorer countries that depend largely on agriculture will be particularly threatened. This calls for immediate actions to mitigate the effects of water scarcity. In spite of its evident scarcity, studies have revealed that the available water is not used efticiently for agricultural production and that large volumes of it are lost every year. ICARDA is, therefore, working with national and international research systems to develop methods of improving water-use efficiency and productivity in agriculture. The first step in these efforts is to assess the existing situation at the farm level and identify the areas where water is not used efticiently. In collaboration with the United Nations Economic and Social Commission for West Asia (ESCWA) and partners in the national research programs of Egypt, Iraq, Jordan and Syria, ICARDA conducted research to develop a practical methodology to evaluate how eff~ciently farmers in the dry areas use water in various agricultural systems, and tested the methodology in various agroecologies in the dry areas. This report summarizes the research results and includes six case studies used to test the developed methodology. We hope that it will contribute to improving water-use efficiency at the farm level, avoiding the loss of water in agriculture, and, therefore, mitigating the effects of water scarcity in the dry areas. Prof. Dr Adel El-Beltagy Director General

4 Acknowledgments The authors would like to thank the NARS of Egypt, Iraq, Jordan and Syria for their active participation in the study. Special thanks are extended to the IPA Agricultural Research Center of Iraq (previous affiliation of the senior author) for developing the methodology and conducting the analyses for the six case studies. Thanks are also due to ICARDA staff, Drs Ahmed Mazied and Pierre Hayek, for collecting data in Syria. Gratitude is also expressed to the lraqi national team, particularly Mr Mahdi Sahar Khaidan (a PhD candidate at the College of Agriculture, University of Baghdad), for collecting field data for the more recent case study of Iraq. We would like to thank the staff of ICARDA's Communication, Documentation and Information Services Unit for their support with editing, typesetting, design and printing this publication. This work was co-funded by the United Nations Economic and Social Commission for Western Asia.

5 Contents Foreword Acknowledgements Contents Executive Summary iii iv v vii Introduction Water-Use Efficiency - Water-use efficiency and productivity - Supplemental imgation and water productivity - On-farm water-use efficiency Methodology Development - The models of water use - Variable input model - Fixed-allocatable input model - Satisficing model - Model validation - Previous research on water allocation On-Farm Water-Use Efficiency in Radwania, Syria - Characteristics of Radwania farms - Model estimation and validation - Empirical results - Water-use efficiency On-Farm Water-Use Efficiency in Rabea, Iraq - Characteristics of Rabea farms - Empirical results - Water-use efficiency On-Farm Water-Use Efficiency in Al Ghor, Jordan - Characteristics of Al Ghor farms - Model estimation and empirical results - Water allocation On-Farm Water-Use Efiiciency in Nubaria, Egypt - Characteristics of Nubaria farms - Empirical results

6 - Results for winter cropping - Results for summer cropping - Water-use efficiency On-Farm Water-Use Efficiency in Beni Sweif, Egypt - Characteristics of the Beni Sweif farms - Empirical results - Winter cropping - Summer cropping - Water-use efficiency On-Farm Water-Use Efficiency in Wheat Production, Iraq - Data and wheat yield of the sample farms - Empirical results - Impact of supplemental irrigation on wheat yield and water productivity - Model estimation and empirical results - On-farm water-use efficiency Conclusions and Recommendations References Appendices

7 Executive Summary The dry areas of West Asia and North Africa (WANA) Pace severe water scarcity due to the limited opportunities for the exploitation of new sources of water coupled with the rapidly growing demand for water resources. As a result, watcr resource management is becoming one of the most important economic and social issues of this century, especially in WANA. Policy makers at all levels and research institutions are increasingly focusing on issues ofwatcr quality and allocation, the increasing demand, changing technologies. water-use efficiency and economic feasibility. Available information indicates that the scarce watcr resources of the region arc inef'ficicntly used, especially for irrigation. Given that irrigation accounts for per cent of all water consumed in the WANA region. improving on-farm water-use efficiency can contribute directly to increased supply of water for other end users. Low irrigation efficiency is associated with poor timing and lack of uniformity of water applications, leaving parts of the field over- or under-irrigated relative to crop needs. Moreover, operators of irrigation systems do not have an incentive to supply farmers with a timely and reliable delivery of water that would be optimal for on-firm watcr efficiency Farmers, on their part, generally tend to over-irrigate as a result of their perceptions of water requirements and their expectations of rainfall and market prices. Most studies in the region on water-use efficiency are based on experimental trials for mono-cropping systems which do not precisely reflect the complexproduction decisions at the farm level under different environmental, technological, and economic conditions. More recently, empirical studies on economic assessment of on-farm water-use efficiency in agriculture were jointly conducted by the International Center for Agricultural Research in the Dry Areas (ICARDA) and the United Nations Economic and Social Commission for Western Asia (ESCWA). These studies clearly demonstrate the low ratios of water-use efficiency in crop production implying the tendency of farmers to over-irrigate their crops. The methodology adopted hy these studies in assessing the status of on-farm water-use efficiency has proved to he a valid approach for conducting further empirical studies. Engineering and agronomy have contributed the majority of literature on water-use efficiency. Efficiency is associated with a transformation of an input into an output. The engineering perspective focuses on the concept of irrigation efficiency, defined as the amount of water from the main water source which can be effectively supplied to the root zone, while the agronomic perspective focuses on the concept vii

8 of crop water-use efficiency, defined as the fraction of water transpired by the crop to that stored in the root zone. This concept includes both crop water-use efficiency and crop-water productivity. A combination of the engineering and agronomic perspectives resulted into the concepts of water-use efficiency, defined as the ratio of transpiration (mm) to total water supply (mm); and water productivity, defined as the ratio of crop production (kg) to the unit of water used These technical measures of efficiency are, however, not sufficient to assess the economic use of water which depends on the relative prices of water and other inputs, the marginal products and prices of the inputs, and the amounts of other inputs, including rainfall. To address this complex situation at farm level, the concept of on-farm water-use efficiency (FWUE) was developed and is defined for the purpose of this analysis as the ratio of the required amount of water for a target production level to the actual amount of water used. The resulting indicators of FWUE are very useful in guiding policies toward improving irrigation efficiency. On-farm water-use efficiency was assessed using six empirical studies jointly conducted by ICARDA and ESCWA. Five case studies were conducted in the Syrian Arab Republic and Iraq in 1999, and Jordan and Egypt in To further support the methodology another case study was conducted in Iraq using farm survey data from a supplemental irrigation project, collected from a cross-sectional survey of 284 farms in Ninavah province in Northern Iraq during the season. The overall objective of this research was to assess the FWUE of crop production under specific farm conditions in some WANA countries. The methodology adopted by these studies has proved to he a valid approach for conducting further empirical studies and the estimated indicators of FWUE will provide useful options for more efficient use of water. To assess the efficiency of on-farm water use, three specified models, namely, the fixed-allocatable input model, variable input model and the behavioral model, were estimated using the ordinary least squares procedure. To validate the estimated models, three sets of out-of-sample forecasts were made. For an out-of-sample prediction, the observations were randomly divided into two subsets, one with 80% and another with 20% of the observations. The 80% subset was used to estimate each model's parameters, which were applied to the 20% to make out-of-sample predictions and to apply the prediction performance measures. To judge the performance of alternative models and thus provide evidence on model choice, three measures of prediction accuracy were applied: the measures of mean absolute error (MAE), root mean square error (RMSE), and mean absolute percentage error (MAPE). Based on the results of the estimated coefficients and

9 two of the comparisons of the prediction performance measures, it was concluded that the fixed-allocatable input model is better at estimating and explaining short-run water use. The selected models were then used to determine the amount of water required by each crop in the six study areas by calculating the amount of water required for each crop at the mean levels of independent variables appearing in each crop's equation. Implications of the results of the estimated coefficients and calculated indices of FWUE are summarized below. When the amount of water required for the crops was compared with actual amount used, it was found that there was over-irrigation for all crops and in all the study areas. FWUE for wheat, for example, was found to be 0.61 in Radwania (Syria): 0.37 in Rabea (Iraq), 0.65 in Nubaria and Beni Sweif (Egypt), 0.30 in A1 Ghor (Jordan), and 0.77 in Ninavah (Iraq). These estimates indicate that farmers over-imgated wheat by 20-60%. It is, therefore, possible to save an enormous amount of water which can be used to expand the wheat growing area, and thus increase total production, or to produce other crops. Alternatively. farmers can increase the wheat yield considerably under current levels of water use, and with improved water and crop management practices. Either option can contribute greatly to food security in WANA. Figure I. Wheat on-farm water-use efficiency (%) in selected areas in WANA.

10 Estimates of FWUE under full irrigation provide important information on the efficiency of water use in producing competing crops. Cotton FWUE was estimated at 0.75 in Radwania and Beni Sweif', rellecting relatively high water-use efficiency compared to other crops produced in these two areas. However, cotton producers exceeded crop requirements by nearly 25%, an amount that could be saved if farmers were provided with extension recommendations to rationalize the use of scarce water. Likewise, FWUE of two forage crops, bersem and corn, produced under full irrigation in Egypt was estimated at These estimates are higher than those of competing crops (0.55 for faba bean and 0.64 for sunflower) produced under similar conditions in Egypt. Figure 2. On-farm water-use effciency of competing crops in Beni Sweif and Nubaria, Egypt. FWUE of vegetable crops varied with crop and area of production. Tomato FWUE was estimated at 0.68 in Rabea, 0.53 in Al Ghor, 0.56 in Beni Sweif, and 0.69 in Nubaria. The FWUE of watermelon was estimated at 0.76 and 0.44 in Nubaria and A1 Ghor, respectively. Similarly, the estimates of pepper FWUF were 0.74 and 0.53 in the same two areas, respectively. FWUE for cucumber and eggplant was 0.56 and 0.66, respectively, in Al Ghor. The estimates of FWUE for cereal, industrial, and vegetable crops mentioned above indicate a wide technological gap between the required practices and actual water application. Therefore, improving water-use efficiency for these crops can contribute greatly to the overall water-use efficiency in the study areas, and offers a high potential for saving water. These results are consistent with the findings of a recent FAO study which concluded that water productivity seems lo be lowest in waler-scarce regions of agriculture-based economies (Bazza and Ahmed, FAO, 2002).

11 Figure 3. Tomato on-farm water-use efficiency in selected areas in WANA. Producers perceive water as a fixed input in the short run, but allocatable among competing crops on the fann. This conclusion is supported by the fact that the coefficient of the water constraint variable is positive in the water-use equations of the crops. The estimates of the individual coefficients of the water constraint suggest that an increase in water availability is allocated most heavily to crops with relatively higher requirements, like cotton, tomato, potato, sugar beet, and bersem, rather than to crops with relatively low water requirements, such as wheat and barley. Output prices and planted areas appear to be strong determinants of water allocation in the short run among competing crops. Moreover, the water price variable is not negative in the water-demand equations for most of the crops in the variable input model. This implies that after planting crops, producers do not respond to water prices in making subsequent short-run decisions. Since water prices in the study areas were highly subsidized, they did not have a major quantitative impact on water allocation. Land allocation, crop choice, irrigation technology and output prices are the main determinants of multi-crop water-use decisions. Previous studies show that water demand is inelastic at low price changes (Fraiture and Perry, 2002). Because water prices are very low in WANA, only high increases in water charges can reduce the amount of water used for irrigation, which in turn will greatly reduce farmer income. Farm yield data from a survey of 284 farms in Iraq provided the following information:

12 Supplemental irrigation increased land and water productivity in wheat systems. Yields in bread wheat increased by 100%, and between 58 and 81% in durum wheat varieties. Water productivity increased by 32 and 15% in bread wheat and durum wheat, respectively, with an average of 31% in all wheat varieties. Irrigation technology has a significant impact on the amount of water used in crop production. Center-pivot sprinkler technology reduced the amount of water used for wheat production in Iraq by 7.2% compared to the use of solidset sprinkler technology. The efficiency of water use varies among different segments of the farmers. Of all the wheat farmers studied in Iraq, 80% had FWUE of less than one, indicating that these farmers over-irrigated their wheat crop, and it was greater than one for 20% of the farmers, implying that these farmers under-irrigated their wheat crop by 10%. The overall water-use efficiency for the whole sample was 0.77, indicating that wheat producers over-irrigated their crop by 23%. Among over-irrigating farmers, the FWUE of 4% was estimated at 0.34, indicating that the actual amount of water used exceeded the required by about 66%. The water-use efficiency of 20% of the farmers was 0.64, implying that this group over-irrigated wheat by 36%. Furthermore, 56% of the farmers had water-use efficiency of 0.87 and over-irrigated wheat by 13%. These results indicate the need for the extension system to develop targeted recommendations for the different farmer groups. Farm size is an important factor in explaining the variation in FWUE among wheat producers. More than 50% of the farmers grew wheat on farms of less than 10 ha, with an average holding of 6.7 ha. The water-use efficiency of such small farms was 0.77, implying that small farmers over-irrigated wheat by 23%. The water-use efficiency of medium farms ( ha) was However, with the increase in farm size above 20 ha, the water-use efficiency decreased. The water-use efficiency of large farms was 0.72, indicating that these farms exceeded water requirements by 28%. Thus, small and medium farms were more efficient than large farms in using supplemental irrigation water in wheat production. This has important implications on the economies of size under supplemental irrigation. The results obtained for the three models used in this study have important policy implications. The overall water-use efficiency for the sample farms was 77%, indicating a potential to improve water-use efficiency by 23%. The results by farm size, on the other hand, show that small, medium, and large farms had

13 different potentials for improving their water-use efficiency by 23, 19 and 28%, respectively. However, each individual farm had a different potential to improve water-use efficiency ranging from a low of 13% to a high of 66%. If policy makers encourage the design of appropriate technical as well as incentive packages, water-use efficiency can be improved. By doing this, ample water will be available for productive use leading to increasing water productivity and consequently agricultural productivity. Improvements in water management, imgation, and technologies have the potential to optimize water use at the farm levels. Sound extension strategies and the provision of pertinent advice to farmers will be instrumental (a) in optimizing water use at farm levels, and (b) in reducing the adverse effects of salinization and water logging on the productivity of land which are caused by over-irrigation. Thus, by obtaining optimal water use it is possible to increase wheat productivity in the study area while ensuring the sustainable use of resources, both water and land. The methods of analysis used in this study were valid for assessing FWUE within the framework of multi-crop production systems. Results obtained compare favorably with expert and technical recommendations. However, these results are only applicable to the study areas and should not be generalized at national and regional levels. The main difficulty encountered in such studies is the calculation of actual water use, given the different sources of water and irrigation technologies used on the farms. It is highly recommended to conduct more empirical studies using similar methods in different agroecological zones of WANA to assess the current status and potential of FWUE for different crops to improve water and land productivity in the region and eventually produce more crops per drop.

14 Introduction Many parts of the world are facing increasing water scarcity. New sources of water are expensive to exploit, limiting any potential for substantial new water supplies. Water for agriculture is increasingly diverted to meet the needs of urban areas and industrial development, while water logging, saliniration, groundwater mining, and water pollution are putting pressure on land and water quality. The majority of the population of people in dry areas of the world are in West Asia and North Africa (WANA). The region is characterized by low rainfall and limited renewable water resources-about 1250 m' per capita. compared to the world average of over 7000 an average of 15,000 m' for Europe, 20,000 for North America and 23,000 m' for Latin America (World Resources Institute, 1999). In some WANA countries, such as Jordan and Tunisia, available water will barely meet basic human needs in the near future. The WANA region receives lower rainfall than seasonal crop water requirements; moreover, its distribution is rarely in a pattern that satisfies crop needs. Periods of severe moisture stress are very common and in most of the locations they coincide with the stages of growth that are most sensitive for crop growth. Soil moisture shortages at some stages cause very low yields. For instance, average rainfed wheat grain yields in WANA range between 0.6 and 1.5 ton/ha, depending on the amount and distribution of seasonal precipitation, much lower than potential yields of over 5 ton/ha. Rapid population growth and improving standards of living are increasing the demand for water in WANA. Presently, over 75% of the renewable watcr resources in the dry areas of the region are used for agriculture. Increasingly, competition for water among various sectors deprives agriculture of substantial amounts every year. It is projected that water for agriculture in WANA will drop from the current level of over 75% to about 50% by Furthermore, most of the hydrological systems are already stretched to the limit, yet more food production is required to feed the increasing population. Greater efforts will have to be made to improve on the efficiency with which water is used if current levels of agricultural production and environmental protection are to be maintained. Thus, water productivity is an urgent issue in the dry areas. High water productivity can be achieved through promoting water-use efficiency techniques, adopting efficient on-farm water management, selecting proper cropping patterns and cultural practices, and developing suitable crop varieties.

15 2 Assessing On-Farm Water-Use Efficiency Yields and water productivity can be substantially improved with the application of supplemental irrigation in the rainfed areas, the adoption of water harvesting in the steppe areas, and the use of improved irrigation systems and schedules in irrigated areas. Water policies in WANA have mainly focused on investment in irrigation, expansion of the irrigated area and construction of drainage networks (ESCWNFAO, 1994), without considering the associated rise in the water table and salinity. These policies have contributed to the depletion of land and water resources in many WANA countries. National water policies could encourage water savings in water-scarce areas by providing incentives and effectively enforcing penalties. When upstream managers cannot ensure conveyance efficiency, there may be no incentives for water users to make efficiency gains. Though water supply for irrigation has expanded the irrigated areas under cultivation and consequently increased agricultural production, lack of demand management practices has contributed to a low efficiency of water use and consequent waste. In addition, improvement in the availability of water due to the introduction of improved technology diverted attention from demand management and reduced emphasis on low-cost alternatives such as improving efficiency, conservation, and reduction of waste through maintenance of irrigation infrastructure. In conventional irrigation, water is applied to maximize crop yield (maximizing production per unit of land). Operators of irrigation systems do not have an incentive to supply farmers with a timely and reliable delivery of water that would be optimal for on-farm water-use efficiency and use of other inputs (Serageldin, 1998). Therefore, farmers generally tend to over-irrigate as a result of their perceptions of water requirements, their expectations of rainfall and market conditions. ICARDA's research on water-use efficiency has shown that yields and water productivity are greatly enhanced by the conjunctive use of rainfall and limited irrigation water. Substantial increases in crop yield were observed in response to the application of relatively small amounts of supplemental irrigation. For wheat growers, supplemental irrigation also stabilized wheat production from one year to another. The coefficient of variation was reduced from 100 to 20% in rainfed fields that adopted supplemental irrigation (Oweis, 2001). ICARDA's long-term research in Syria has shown that applying only 50% of full supplemental irrigation requirements (over that of rainfall) would cause a reduction in yield of 10-15%. This finding, in light of the increasing water scarcity in Syria,

16 Water-Use Efficency 3 encouraged ICARDA and the extension system to test a deficit supplemental irrigation strategy at farmers' fields. Results show that with deficit irrigation the yields increase by over 50% compared with full irrigation, which demonstrates the possibility of producing more food with less water. Information on on-farm water-use efficiency in WANA is limited (Oweis and Hacum, 2003). Most of the evidence available in the region is mainly based on experimental trials for mono-cropping systems. Thus, it does not precisely reflect the complex production decisions at the farm level under different environmental, technological, and economic conditions. Recently, six empirical studies on economic assessment of on-farm water-use efficiency in agriculture were conducted. These studies clearly demonstrate the low ratios of water-use efficiency in crop production, implying the tendency of farmers to over-irrigate their crops (ESCWAIICARDA, 2000,2001,2003). The main objective of this work was to empirically quantify the status of water-use efficiency under farmers' conditions using a tested methodology for the assessment of on-farm water-use efficiency in the WANA countries. Specifically, the studies were aimed at developing a methodology for the assessment of on-farm water-use efficiency within the framework of multi-crop production systems. The approach was tested in selected areas of Egypt, Iraq, Jordan and Syria using farm survey data. Some of the concepts used here and the case studies were reported earlier in ESCWA-ICARDA joint documents (ESCWA/ICARDA, 2000,2001, and 2003).

17 4 Assessing On-Form Water-Use Efficiency Water-Use Efficiency Water-Use Efficiency and Productivity The concept of water-use efficiency (WUE), commonly used to evaluate the performance of an irrigation system, is defined as the ratio of the amount of water used for an intended purpose to the total amount of water input within a spatial domain of interest. In this context, the amount of water applied to a domain of interest but not used for the intended purpose is a loss. To increase the efficiency of a domain of interest, it is important to identify and minimize losses. Depending on the intended purpose and the domain of interest, there are many efficiency concepts, such as crop water-use efficiency and water-application efficiency, among others (Guerra et al., 1998). Improving irrigation efficiency is a slow but difficult process that depends essentially on the local water scarcity situation. It may be expensive and requires willingness, know-how and action at various levels. Efficient use of irrigation has been studied for three types of systems: the trickle, solid-set sprinkler, and furrow irrigation systems. It was found that imgation efficiency of the sprinkler system was on the average about 22% more than that of the furrow system and about 21% less than that of the trickle system. Overall efficiency of the trickle system, however, was on average about 28 and 45% more than that of the sprinkler and furrow systems, respectively (Dawood and Hamad, 1985). The WUE concept is not directly related to the amount of food that can be produced with an amount of available water. The optimum level of applied water for a particular situation is that which produces the maximum profit or crop yield per unit of land or per unit of water, depending on the underlying objective function and the limiting factor. In this respect, water productivity, defined as the amount of food produced per unit volume of water used, is more relevant. Because the water used may have various components-evaporation, transpiration, gross inflow. net inflow, and others-it is essential to specify which components are included when calculating water productivity. The concept of water productivity, like WUE, requires clear specification of the domain of interest. Water productivity can be improved by increasing yield per unit of the land area using a better crop variety, improved agronomic practices, or by growing the crop during the most suitable period. Thus, water productivity can be achieved by factors other than water management. Higher productivity does not necessarily mean that the crop effectively uses a higher proportion of the water input. For this reason, water productivity alone would not be particularly useful in identifying water-saving opportunities of the system under consideration.

18 Water-Use Efficency 5 The terms WUE and water productivity should be used complementarily to assess the impact of water management strategies and practices used to produce more crops with less water. However, both terms are scale-sensitive; therefore, failure to clearly define the boundaries of the spatial domain of interest can lead to erroneous conclusions. It is also vital to specify the water-use components that are taken into account when deriving water-use efficiency and productivity. Furthermore, the two concepts of efticiency and productivity are related but different. Due to the scarcity of water, there is a need to evaluate the efficiency with which it is utilized to arrive at an appropriate irrigation system. WUE and productivity would differ according to different systems of irrigation, crop mix and environment, and are comprised of different dimensions: crop consumptive use (water requirement), an efficient crop mix (maximum irrigable area for given water resources) and maximum output and value per unit of water. Measurements of efficiency or loss are site-specific not only because of variation in physical environment, but also because of variation in the physical infrastructure and management capacity reflected at each location. For measuring water productivity, while the denominator remains the quantity of water diverted or depleted for a particular use, such as crop production, the numerator is measured as the crop output. The numerator and the denominator can be expressed in either physical or monetary terms. Given this measure, there are several different ways of expressing water productivity: Pure physical productivity, defined as the quantity of the product divided by the quantity of the water diverted or depleted; Combined physical and economic productivity, defined in terms of the economic value expressed as gross or net value, or net present value divided by the amount of water diverted or depleted; Economic productivity, defined as the net present value of the product divided by the net present value of the amount of water diverted or depleted (defined in terms of its value or opportunity cost, in the highest alternative use). In this context, many researchers frequently use the term water productivity as the ratio of the physical yield of a crop and the amount of water consumed, including both rainfall and supplemental irrigation. Yield is expressed as a mass (kg or ton), and the amount of water as a volume Water productivity has been evaluated in terms of crop output and value per unit of water. A protective irrigation system was found to perform better in terms of social efficiency, and a perennial system was better in terms of situational efficiency. In India. the yield rates of rice, for example, in the irrigation system were higher than those under the perennial system, although the water requirement was lower. The

19 6 Assessing On-Farm Wafer-Use Efficiency average water productivity of rice in physical and monetary terms was 0.25 kg/m3 and Rs/m3 under the protective system of irrigation. All other crops had higher water productivity. In the perennial system, the water productivity of rice was lower, but the crop was widely grown during the rainy season because of the agro-climate (Giriappa, 1984). Supplemental Irrigation and Water Productivity Supplemental irrigation (SI) can be defined as the addition of small amounts of water to rainfed crops when rainfall fails to provide sufficient moisture for normal plant growth, in order to improve and stabilize yields. The cost of water is an important factor in the economics of SI. In most WANA countries, water from public (surface) irrigation schemes is provided almost free to users; and groundwater costs do not reflect their real value, because the energy required for pumping is highly subsidized. As a result, most farmers tend to over-irrigate. ICARDA studies have shown that the SI amounts for wheat reported by farmers is up to three times the optimal rate from research trials. It is common to see sprinklers operating on wheat in December, January and February, when the probability of rain is high, even though the crop water requirement in these months is low and the crop is not very sensitive to water stress. Enhanced exploitation of groundwater for SI on vast areas, which traditionally used to be rainfed, has helped bridge the gap, for example, in the Syrian Arab Republic's basic food production, recovering in particular the wheat balance. However, it has led to over-pumping and excessive water use. Results show that improving the wheat price encourages the use of more water, unless the rate of increase in the cost of water exceeds that of wheat. Optimal applications of SI are determined by both the input/output price ratio and weather conditions. Research by ICARDA scientists also shows that in the Syrian Arab Republic, supplementing only 50% of the rainfed crop irrigation requirements reduces the grain yield by only 10.20% relative to full irrigation (FI). Using the saved 50% to irrigate an equal area gives a much greater return in the total production. In some areas, groundwater resources are being over-exploited for FI and their quality is deteriorating. With such pressure on the existing water resources, sustainable use can be obtained only by producing more crops from less water-improving water productivity. Comparing the water productivity of SI in wheat with that of FI, a real opportunity for water-use improvement was found. According to ICARDA's research trials on farmers' demonstration fields in the Syrian Arab Republic, a cubic meter of water used in SI produced, on average, an extra 3kg of wheat over rainfed yield, whereas

20 a cubic meter used in FI produced about 0.5kg/m 3. This large difference in the water productivity is attributed to the conjunctive use of rainfall and S1 water. In Jordan, water productivity in rainfed wheat in Mushagar (300mm annual rainfall) was 0.33kg/m3. When a cubic meter of rainfall was combined with SI of 0.5m 3, the overall water productivity was increased to 3.5kg/m3. In view of this potential for more efficient use of water decision makers at the national levels should consider the feasibility of diverting some irrigation water from FI to SI or use both for optima1 crop-water allocation (Oweis and Salkini, 1992). The average water productivity of rain in producing wheat in the dry areas of West Asia and North Africa is about 0.35kg of although with good management and favorable rainfall (in amount and distribution) it can be increased to lkg of However, water used in SI can be much more productive. ICARDA research showed that a cubic meter of water applied at the right time (when the crop is suffering from moisture stress), combined with good management, could produce more than 2.5kg of grain over the rainfed production. This extremely high water productivity is mainly attributed to the effectiveness of a small amount of water in alleviating severe moisture stress during the most sensitive stage of crop growth and seed-filling. When SI water is applied before such conditions occur, the plant may reach its yielding potential (Oweis, 1997). In comparison to the productivity of water in fully irrigated areas (where the effect of rainfall is negligible), the productivity is higher with SI. In fully imgated areas with good management, wheat grain yield is about 6 tons/hectare using 800 mm of water. Thus, the water productivity is about one-third of that under SI with similar management. This suggests that water resources may be better allocated to SI when other physical and economic conditions are favorable. On-Farm Water-Use Efficiency The term "efficiency" reflects the ratio of output to input. However, input and output components of efficiency differ from one field to another. Even in the same field. these components vary depending on the level and/or scope at which the term "efficiency" is being used. In irrigated agriculture, there are many efficiency terms, each of which has a specific use. These terms include: Water-Conveyance Efficiency (WCE), which reflects losses of water from the conveyance system; Water-Application Efficiency (WAE), which reflects losses of water below the crop root zone; Water-Distribution Efficiency (WDE), which reflects how uniformly water is applied to the field; Water-Storage Efficiency (WSE), which reflects the adequacy of water stored in the crop root zone;

21 8 Assessing On-Farm Water-Use Efficiency Irrigation Efficiency (IE), which reflects the overall losses in irrigation; and Water-Use Efficiency (WUE), which reflects how well water is used in producing crops. The common factor or resource that ties these terms is water (Oweis and Hachum, 2002). WUE has been defined in various ways by hydrologists, physiologists and agronomists, depending on aspects that one wishes to emphasize. For instance, Viets (I 962) used WUE to characterize the ratio of crop yield to crop water use. WUE, in general, refers to the amount of plant material produced per unit of water used. WUE is not a physical engineering efficiency, which is usually dimensionless and has a maximum value of 100%. The efficiency term for this biological ratio has caused some concern and confusion with irrigation and water resources efficiency terms. Although efficiency is a measure of output per unit input, we rarely consider all the outputs or all the inputs involved in crop production; therefore, the term should be used cautiously. Plant growth and yield are more strongly related to transpiration than to evapotranspiration. However, WUE is sometimes evaluated per unit of water transpired (WUET), or per unit of irrigation water applied (WUEI). Often, WUE is based on evapotranspiration (WUEET). The difference is important since suppression of soil evaporation and prevention of weed transpiration can improve the WUEET; however, it need not improve the WUET, which is a measure of crop performance. I-WUEET is a measure of the increase in the crop production (biomass or marketable component) relative to the increase in water consumed when irrigated, over the consumption under non-irrigated conditions as follows, (Burman et al., 1981): Where: Y, = mass of marketable crop produced with irrigation Y,, = mass of marketable crop produced without irrigation = mass of water used in ET by the irrigated crop Et, = mass of water used in ET by the non-irrigated crop To further explain WUE terms, Figure 4 depicts, under normal field conditions, the relation between crop yield (Y) and each of transpiration (T) evapotranspiration (ET) and irrigation water (1). From the diagram, the transpiration WUE (WUET), the evapotranspiration WUE (WUEET) and the irrigation WUE (WUEI) are defined as: WUET = Y/T (2)

22 WURET = Y/(T+E:) (3) WUEI Y/(T+E+(I-r1 r2)(r+d)) (4) Where: R= surface runoff losses D= deep percolation (drainage) losses rl= Sraction of (R+D) that is recoverable with water quality the same as that of the irrigation water, I r2 = reduction in the water productivity potential due to deterioration in water quality; depends on water quality of 1 and rl(r+d), (rl I) It is evident that: WUEI < WUEET< WUET. However, if E=0, then WUEET = WUET. Also if the runoff(r) and drainage (D) losses are equal to zero, then WUEI = WUEET, and so on. The concept of WUE has many facets, but the most relevant are physiological, agronomic, hydrological and socioeconomic. The current definition of WUE is not necessarily accepted by scholars in all of these fields, this is why Hook and Goscho (1988) have proposed the concept of resource-use efficiency (RUE). RUE considers all the components of production inputs including land, water, climate, nitrogen, and cropping systems. When one resource is limiting yield, other non-limiting resources are usually used less efficiently. When that which limits yield is alleviated, all resources will be used more efficiently until another resource becomes limiting. Considering that water in the dry areas is often the most limiting resource, any improvement in water RUE will necessarily lead to enhanced use of other resources. The engineering and agronomy perspectives have dominated the literature on WUE. In the engineering perspective the concept of irrigation efficiency is detined as the amount of water from the main water source which can be effectively supplied to the root zone. This perspective distinguishes between three types of efliciency, namely; conveyance efficiency, farm efficiency and field efficiency (Schmidt, 2001). The agronomic perspective, however, illustrates the concept of crop WUE, detined as the fraction of water stored in the root zone that is transpired by the crop. This concept includes both crop WUE and crop water productivity. A combination of the agronomic and engineering perspectives results in WUE, defined as the ratio of transpiration (mm) to total water supply (mm), and water productivity, defined as the ratio of yield (kg) to total water supply (mm). These concepts reflect the technical measures of efficiency and thus are not sufficient to assess the economic level of water-use efficiency, as water is used in combination with a whole set of other inputs, such as land, fertilizers, labor,

23 10 Assessing On-Farm Wafer-Use Efficiency machinery, and management, to produce crops. Therefore, singling out any one input such as water to determine efficiency may be misleading (ACIL Tasman, 2003). The economically efficient amount of water use depends on the relative prices of water and other inputs, the marginal products of the inputs, the prices of inputs and the amounts of other inputs, including rainfall. The concept of on-farm water-use efficiency (FWUE) was developed to address this complex situation at the farm level (ESCWA/ICARDA, 2000 and 2001). FWUE is defined as the ratio of the required amount of irrigation water to produce a specific output level to the actual amount of water applied by farmers. With this definition FWUE may take the value of less than, greater than or equal to one. If it is less than one, it implies that farmers over-irrigate their crops. While a value greater than one implies that farmers under-irrigate the crops. However, if the value of the calculated FWUE is equal to one, it means that farmers are fully efficient in using irrigation water because the required and applied amounts of water use are equal. FWUE = X 100% Where: is the amount of water required (m 3 ) by the crop to produce certain level of crop production is the amount of water actually applied (m 3 ) by the farmer to produce that level of crop production This definition combines several aspects from others mentioned earlier; however, its advantage is that the nominator and denominator are of the same units (volume or depth), so the efficiency can be expressed as a percentage. The efficiency definition also reflects the performance of the farmer in using water relative to the resources potential and farm conditions that exist in the area surveyed and not to another area with different farming conditions. The water required in the above equation is determined by the model from the data collected among the complete sample at the community. the canal or the district level. FWUE was assessed using six case studies in Egypt, Iraq, Jordan and Syria (ESCWA/ICARDA 2000,2001, and 2003). These case studies support the usefulness of this concept to assess the efficiency of water use under farmers' conditions and provide vital information for water savings. FWUE in Radwania (Syria), for instance, was found to be 0.61 for wheat, 0.45 for barley and 0.75 for cotton. The estimates indicate that farmers over-irrigate wheat, barley and cotton by 39, 55 and 25%, respectively. Other case studies provide similar information regarding the excessive use of irrigation water by crop producers.

24 Methodology Development 11 Methodology Development Predicting crop-level input allocation (use) is a major problem in a multi-crop production system largely due to limited availability of data on crop-level input use. The challenge, therefore, is to develop modeling approaches that permit prediction of input allocation from data on farm-input use and crop-level land use. These modeling approaches are needed to develop crop budgets and estimates of costs of production. Furthermore, to evaluate the effects of alternative policies on input use requires an understanding of how producers make decisions on crop-level input use (Moore et al., 1994). Previous research on multi-output input allocation was mainly based on two assumptions about producer behavior: profit maximization and satisficing. Satisficing behavior means that farmers operate on the basis of rules of thumb-basing entirely on their practical experience and not so much on scientific evidence. A simple form of this is that producers follow either a distributor's recommendation or other routine practices concerning a crop's input-application rate per hectare. Crop acreage would, therefore, effectively determine the allocation of an input among crops on a multi-crop farm. The Models of Water Use Three alternative models of multi-crop input allocation are proposed for this study. These are the fixed-allocatable input model, the variable input model, and the satisficing model. An input considered to be variable in the long run may actually be fixed and allocatable in the short run. Irrigation with ground water is, for example, modeled as a variable input in the long run based on the assumption that it is subject to market forces with groundwater-pumping costs as water 'price'. Yet constraints on the number of wells, pump capacity, and water distribution infrastructure may make groundwater a fixed-allocatable input in the short run (Moore et al., 1994b). Irrigation with surface water may pose similar short- and long-run institutional constraints. Hired labor and farm machinery may also be variable in the long run, but fixed and allocatable in the short run. Crop-level input-use data are required to estimate the fixed-allocatable input model. Farm-level water use serves as an exogenous variable in this model, with crop-level water use serving as the endogenous variable. Unlike the variable input and satisficing models, a procedure does not appear to be available for predicting the results of the fixed-allocatable input model using deficient data because of the essential role of farm-level water as an exogenous variable. In contrast, farm-level water serves as the endogenous variable in the variable input and satisficing models estimated with deficient data. A data set that contains both crop-level irrigation water and acreage data from multi-crop farms is applied.

25 The three alternative models of short-run input use can bc directly estimated econometrically with crop-level water data. The availability of crop-level micro data on WUE makes the data 'non-deficient' in terms of information on water a llocation in a multi-crop system. In this study, the variable input and the fixedallocatable input models are derived based on the profit maximization assumption. The satisficing model is a simple model of bounded rationality. These three models of multi-crop water allocation can be compared using two techniques of model selection-model specification tests and prediction accuracy measures. The empirical application analyzes multi-crop water irrigation in Syria, Iraq, Jordan and Egypt using data from farm surveys. The basic unit for the analysis is the individual farm and the study targeted the whole cropping system. WUE was assessed for all crops planted in a given season and for all seasons over the year. Different farms were selected to cover the following major conditions in the region: Water sources including surface and ground water and rainfall. Cropping systems including field crops, orchards, vegetables and mixed systems. Water managemenl systems including rainfed, SI, and FI. Farm size and type including small, medium and large. Farmers involved in irrigated agriculture make a variety of decisions concerning crop-choice, land use, and irrigation water application. As an irrigator, the farmer also makes crop-level water decisions conditional on land allocations, which determine water use within an irrigation season (Moore et al., 1994b). In this analysis, the farmer makes intermediate production decisions including the acreage and combination of crops. Subsequent short-run decisions include quantity of irrigation water to apply to each crop over the irrigation season. Thus, crop-specific acreages are exogenous to the water-use decisions. The common thread across the three alternative models, according to Moore et al. (1994a) is that crop-level land use serves as one of the determinants of crop-level water use in each model. To mathematically present the proposed models, the following notation is used: P = crop prices which are given to producers = price of crop i, (i= I,...,m) = water price r = variable input prices other than water (v= 1,..., z) = water allocated to crop i W = farm-level quantity of water n, = land allocated to crop i