Irrigation water use efficiency

Traditional transplanted rice with continuous standing water in Asia has relatively high water inputs. Because of increasing water scarcity, there is a need to develop alternative systems that require less water. This paper reports results of on-farm experiments in the Philippines to reduce water input by water-saving irrigation techniques and alternative crop establishment methods, such as wet and dry seeding. With continuous standing water, direct wet-seeded rice yielded higher than traditional transplanted rice by 3-17%, required 19% less water during the crop growth period and increased water productivity by 25-48%. Direct dry-seeded rice yielded the same as transplanted and wetseeded rice, but can make more effective use of early season rainfall in the wet season and save irrigation water for the subsequent dry season. Direct seeding can further reduce water input by shortening the land preparation period. In transplanted and wet-seeded rice, keeping the soil continuously around saturation reduced yields on average by 5% and water inputs by 35% and increased water productivity by 45% compared with flooded conditions. Intermittent irrigation further reduced water inputs but at the expense of increased yield loss. Under water-saving irrigation, wet-seeded rice out-yielded transplanted rice by 6-36% and was a suitable establishment method to save water and retain high yields. Groundwater depth greatly affected water use and the possibilities of saving water. With shallow groundwater tables of 10-20 cm depth, irrigation water requirements and potential water savings were low but yield reductions were relatively small. The introduction of water-saving technologies at the field level can have implications for the hydrology and water use at larger spatial scale levels. # (B.A.M. Bouman).

Despite the impressive gains in global food production over the last half century, an estimated 790 million people remain hungry. Many of the chronically hungry are poor farm families, who have neither the means to produce the food they need nor sufficient income to purchase it. For them, access to irrigation water, or the means to use the water they have more productively, is a key to increasing their crop production, their incomes, and their household food security. Ironically, a technology typically associated with wealthy farmers, drip irrigation, may hold the key to alleviating a significant share of rural hunger and poverty. A new spectrum of drip systems keyed to different income levels and farm sizes (beginning with a US$5 bucket kit for home gardens) now exists and can form the backbone of a second green revolution, this one aimed specifically at poor farmers in sub-Saharan Africa, Asia, and Latin America. We describe the experience with affordable drip irrigation to date, including its growing use in India and Nepal, as well as the wide range of geographic areas and conditions where these systems may be useful. We propose a major new international initiative to spread low-cost drip irrigation through private microenterprise, with the aim of reducing the hunger and increasing the incomes of 150 million of the world's poorest rural people over the next 15 years. Our estimates suggest that such an initiative could boost annual net income among the rural poor by some US$3 billion per year and inject two or three times this amount into the poorest parts of the developing world's economies.

Irrigation water accounts for almost 40% of total variable production costs for rice (Oryza sativa L.) cropping in the Burdekin River Irrigation Area, northern Australia. Increasing the efficiency of water use would improve the economic viability of growers and long-term environmental benefits would also be likely due to lower water tables and decreased salinisation in irrigation areas. The aim of these studies was to maximize grain yield by optimizing its functional components: water use, efficiency of water use for dry matter production (WUEdm) and harvest index (HI). The responses of dry matter and yield in rice (cv. Lemont) to five methods of irrigation were studied in a wet and dry season in the region. Applying a permanent flood at sowing, the 3-leaf stage (traditional) and prior to panicle initiation were compared with two unflooded methods: saturated soil culture (SSC) and intermittent irrigation at weekly intervals. Saturated soil culture consisted of growing rice on raised beds of height 0.2 m and width 1.2 m, with water maintained in the furrows (0.3 m wide) some 0.1 m below the bed surface.

Water price reforms are increasingly being used to encourage improvements in irrigation efficiency through technology adoption. A microparameter approach based on field-level data is used to assess the effect of economic variables, environmental characteristics, and institutional variables on irrigation technology choices. The results show that water price is not the most important factor governing irrigation technology adoption; physical and agronomic characteristics appear to matter more. The results demonstrate the importance of using micro-level data to determine the effects of asset heterogeneity and crop type on technology adoption.

Water resources are limited for irrigation worldwide; therefore, there is a need for water-saving irrigation practices to be explored. Partial root-zone drying (PRD) is a new water-saving irrigation strategy being tested in many crop species. Experiments were conducted in potato (Solanum tuberosum L. cv. Folva) under open field conditions in 2004 and under a mobile rainout shelter in 2005. Two subsurface irrigation treatments were studied: full irrigation (FI) receiving 100% of evaporative demands, 50.1 and 201 mm of irrigation water in the 2 years, to keep it close to field capacity; and PRD, which received 21.7 and 140 mm of irrigation in 2004 and 2005 respectively. Due to rain in 2004, the PRD treatment was imposed over a short period only during the late tuber filling and maturing stages. In 2005, the PRD treatment was imposed during the whole period of tuber filling and tuber maturation. The PRD treatment was shifted from one side to the other side of potato plants every 5–10 days. Especially in 2005 it was apparent that stomatal conductance was generally lower in the PRD than in the FI plants, whereas leaf water potential tended to be lower in only a few instances. During the treatment period, plants were harvested five times, and no significant difference was found between the treatments in leaf area index, top dry mass and tuber yield. At final harvest, tubers were graded based on size into four classes C1–C4, of which the yield of the important marketable class (C2) was significantly higher (20%) in the PRD than in the FI treatment. Compared with FI, the PRD treatment saved 30% of irrigation water while maintaining tuber yield, leading to a 61% increase of irrigation water use efficiency. The limited data of 2004 support these results. In summary, PRD is a promising water-saving irrigation strategy for potato production in areas with limited water resources.

Rapidly depleting unconfined aquifers are the primary source of water for irrigation on the North China Plain. Yet, despite its critical importance, groundwater recharge to the Plain remains an enigma. We introduce a one-dimensional soil-water-balance model to estimate precipitation-and irrigation-generated areal recharge from commonly available crop and soil characteristics and climate data. To limit input data needs and to simplify calculations, the model assumes that water flows vertically downward under a unit gradient; infiltration and evapotranspiration are separate, sequential processes; evapotranspiration is allocated to evaporation and transpiration as a function of leaf-area index and is limited by soil-moisture content; and evaporation and transpiration are distributed through the soil profile as exponential functions of soil and root depth, respectively. For calibration, model-calculated water contents of 11 soildepth intervals from 0 to 200 cm were compared with measured water contents of loam soil at four sites in Luancheng County, Hebei Province, over 3 years (1998)(1999)(2000)(2001). Each 50-m 2 site was identically cropped with winter wheat and summer maize, but received a different irrigation treatment. Average root mean-squared error between measured and model-calculated water content of the top 180 cm was 4Ð2 cm, or 9Ð3% of average total water content. In addition, model-calculated evapotranspiration compared well with that measured by a large-scale lysimeter. To test the model, 12 additional sites were simulated successfully. Model results demonstrate that drainage from the soil profile is not a constant fraction of precipitation and irrigation inputs, but rather the fraction increases as the inputs increase. Because this drainage recharges the underlying aquifer, improving irrigation efficiency by reducing seepage will not reverse water-table declines.

In this paper, an economic optimisation model for hydrologic planning in de®cit irrigation systems is proposed. Irrigation water allocation between agricultural demands is carried out following an economic ef®ciency criterion with the aim of maximising the overall economic bene®ts obtained, allocating available water to each user as a function of the water's pro®t margin. Water resources constraints in the system are considered. Aggregated economic functions for each irrigation district are generated optimising the water used for the cropping pattern. Stochastic nature of water availability and irrigation requirements have been taken into account.

In search of new innovations for saving irrigation water, fruit yield response and N-fertiliser recovery of greenhouse grown spring-planted tomato (Lycopersicon esculentum Mill., cv. F1 Fantastic) were assessed as influenced by deficit irrigation, imposed using either conventional deficit irrigation (DI) or partial root drying (PRD). Three irrigation treatments were tested: (1) FULL, control treatment where the full amount of irrigation water, which was measured using Class-A pan evaporation data, was applied uniformly on the two halves of plant-root zone; (2) PRD, 50% deficit irrigation in which wetted and partially dry halves of the root-zone were interchanged every irrigation; (3) DI, conventional deficit irrigation maintained at 50% deficit, compared to FULL irrigation, with water applied on the both halves of the root-zone. During a growth period of 153 days, the highest fruit yield of 145.4 t ha −1 was measured under FULL irrigation treatment, which was followed by PRD and DI treatments with statistically lower (P ≤ 0.01) yields of 114.6 and 103.4 t ha −1 , respectively. Irrigation water use efficiencies (IWUE) of both deficit treatments were significantly (P ≤ 0.01) higher (52.7% for PRD and 38.3% for DI) compared to FULL irrigation. Nitrogen-fertiliser recovery was over 70%, with no significant difference among the irrigation treatments. Both deficit treatments (DI and PRD) showed lower values of leaf water potential, photosynthetic rate and stomatal conductance compared to FULL irrigation. Before irrigation, xylem-sap abscisic acid (ABA) concentrations were 28% and 38% higher under water-stressed deficit treatments DI0 and PRD, respectively, compared to FULL irrigation, and the high ABA concentrations was maintained only under PRD effect, following irrigation. The results of this work suggest that PRD practices can be viable and advantageous compared to conventional techniques to minimise crop-yield reductions during deficit irrigation.

Due to the decreasing availability of water resources and the increasing competition for water between residential, industrial, and agricultural users, increasing irrigation efficiency, by methods like subsurface drip irrigation (SDI) systems, is a pressing concern for agricultural authorities. To properly manage SDI systems, and increase the efficiency of the water/fertilizer use while reducing water losses due to evaporation, the precise distribution of water around the emitters must be known. In this paper, the Windows-based computer software package HYDRUS-2D, which numerically simulates water, heat, and/or solute movement in two-dimensional, variably-saturated porous media, was used to evaluate the distribution of water around the emitter in a clay loam soil. The simulation results were compared with two sets of laboratory and field experiments involving SDI with emitters installed at different depths, and were evaluated using the root-mean-square-error (RMSE). The RMSE at different locations varied between 0.011 and 0.045 for volumetric water contents, and between 0.98 and 4.36 cm for wetting dimensions. Based on these values, it can be concluded that the correspondence between simulations and observations was very good.

A common policy prescription for conserving irrigation water is to promote more efficient or "water-saving" irrigation technologies. We develop a risk programming model to quantify the effect of irrigation efficiency on irrigation water use in the High Plains, taking account of irrigation timing and well capacity limits. We find that optimal irrigation does not respond monotonically to changes in efficiency, although intermediate and high efficiency systems both result in less water use than an inefficient flood system.

This study was conducted to determine appropriate irrigation frequencies and water-yield relationship for sweet corn irrigated by drip irrigation system in a semi-arid region. The research was carried out at the Agricultural Research Station of Harran University in Sanliurfa, Turkey, in 1998 and 1999. In the study, water was applied to sweet corn as 100, 90, 80 and 70% of evaporation from a Class A Pan corresponding to 2-, 4-, 6-and 8-day irrigation frequencies, respectively. Irrigation water applied to crops ranged between 610 and 876 mm in 1998, while 612-889 mm of water was applied in 1999. The highest values for total water use efficiency (TWUE) were found to be 1.38 and 1.24 kg m À3 in the 4day irrigation frequency in 1998 and 1999, respectively. The highest values for irrigation water use efficiency (IWUE) were determined to be 1.66 kg m À3 in the 4-day irrigation frequency in 1998 and 1.59 kg m À3 in the 6-day irrigation frequency in 1999. Crop response factor (k y) ranged from 0.76 to 1.22 in 1998 and from 0.96 to 1.29 in 1999. Fresh ear yield, based on the irrigation frequencies, was found to be statistically significant (ÃÃ P < 0:01) in both years. The highest fresh ear yields were 13.66 and 13.19 t ha À1 for the 2-day irrigation frequency in 1998 and 1999, respectively. The minimum fresh ear yields were found to be 8.55 and 7.29 t ha À1 with the 8-day irrigation frequency in 1998 and 1999, respectively. Yield was reduced with deficit irrigation in both years. The results of this research indicate that a 2-day irrigation frequency, with 100% ET water application by a drip system, will be optimal for sweet corn grown in semi-arid regions similar to that in Turkey where the work was conducted.

It is important to promote ef®cient use of water through better management of water resources, for social and economical sustainability in arid and semi-arid areas, under the conditions of severe water shortage. Based on the developments in de®cit irrigation research, a recurrence control model for regional optimal allocation of irrigation water resources, aiming at overall maximum ef®ciency, is presented, with decomposition-harmonization principles of large systems. The model consists of three levels (layers). The ®rst level involves dynamic programming (DP) for optimization of crop irrigation scheduling. The second level deals with optimal allocation of water resources among various crops. The last level concerns optimal allocation of water resources among different sub-regions. As a test, this model was applied to the combined optimal allocation of multiple water resources (surface, ground and in-take from the Weihe river) of Yangling, a semi-arid region on the Loess Plateau, China. Exemplary computation showed that not only are the results rational, but the method can also effectively overcome possible``dimensional obstacles'' in dynamic programming of multiple dimensions. Furthermore, each sub-model is relatively independent by using various optimization methods. The model represents a new approach for improving irrigation ef®ciency, implementing water-saving irrigation, and solving the problem of water shortage in the region studied. The model can be extended in arid and semi-arid areas for better water management. #

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 6 ( 2 0 0 9 ) 8 6 6 -8 7 4 a b s t r a c t During 2 years, a melon crop (Cucumis melo L. cv. Sancho) was grown under field conditions to investigate the effects of different nitrogen (N) and irrigation (I) levels on fruit yield, fruit quality, irrigation water use efficiency (IWUE) and nitrogen applied efficiency (NAE). The statistical design was a split-plot with four replications, where irrigation was the main factor of variation and N was the secondary factor. In 2005, irrigation treatments consisted of applying daily a moderate water stress equivalent to 75% of ETc (crop evapotranspiration), a 100% ETc control and an excess irrigation of 125% ETc (designated as I 75 , I 100 and I 125 ), while the N treatments were 30, 85, 112 and 139 kg N ha À1 (designated as N 30 , N 85 , N 112 and N 139 ). In 2006, both the irrigation and N treatments applied were: 60, 100 and 140% ETc (I 60 , I 100 and I 140 ) and 93, 243 and 393 kg N ha À1 (N 93 , N 243 and N 393 ). Moderate water stress did not reduce melon yield and high IWUE was obtained. Under severe deficit irrigation, the yield was reduced by 22% mainly due to decrease fruit weight. The relative yield (yield/maximum yield) was higher than 95% when the irrigation depth applied was in the range of 87-136% ETc. In 2006, the interaction between irrigation and N was significant for yield, fruit weight and IWUE. The best yield, 41.3 Mg ha À1 , was obtained with 100% ETc at N 93 . The flesh firmness and the placenta and seeds weight increased when the irrigation level was reduced by 60% ETc. The highest NAE was obtained with quantities of water close to 100% ETc and increased as the N level was reduced. The highest IWUE was obtained with applications close to 90 kg N ha À1 . The I 243 and I 393 treatments produced inferior fruits due to higher skin ratios and lower flesh ratios. These results suggest that it is possible to apply moderate deficit irrigation, around 90% ETc, and reduce nitrogen input to 90 kg ha À1 without lessening quality and yields. (F. Ribas).

Scarcity and competition for water are matters of increasing concern, as are potential shortages of food. These issues intersect both within the agricultural sector and across all water using sectors. Irrigation is by far the largest user of water in most water-scarce countries, and is under pressure to reduce utilisation (to release water to other sectors, including the environment) and use water more productively to meet demands for food and fibre. The terminology for such intra-and inter-sectoral analysis must be unambiguous across sectors so that interventions and their impacts are properly understood. Such terminology, based on previous work and debate, is set out. Implications for a better understanding of the scope for improved productivity of water in agriculture are traced, and some examples are given using data from recent research submissions, demonstrating the benefits of precise water accounting.

Farming in Serbia is traditionally rainfed. Analyses show that drought events of varying severity are frequent in this region, although there is no specific pattern. There is a distinct need for an objective assessment of the impact of drought on strategic field crops, to solve the dilemma whether irrigation is required or not. For this reason, and based on available field data, the FAO AquaCrop water driven model was selected to simulate yield and irrigation water use efficiency (IWUE) for three major field crops (maize, sunflower, and sugar beet), under two scenarios: (1) natural water supply and adequate supply of nutrients, and (2) supplementary irrigation and adequate supply of nutrients. The experiments presented here were conducted between 2000 and 2007 in northern Serbia, where chernozem soil is prevalent. Data of 2003 cropping seasons were used for local calibration, whereas the remaining years for validation. Results were such that local calibration resulted in very minor changes of AquaCrop coefficients (e.g., maize basal crop coefficient, sunflower harvest index, etc.). Simulated maize yield levels exhibited the greatest departure from measured data under irrigation conditions (−3.6 and 3.3% during an extremely dry and an extremely wet year, respectively). Simulated sunflower yield levels varied by less than 10% in 8 out of 10 comparisons. The most extreme variation was noted during the extremely wet year. The difference between simulated and measured values in the case of sugar beet was from −10.2 to 12.2%. Large differences were noted only in two or three cases, under extreme climatic conditions. Statistical indicators-root mean square error (RMSE) and index of agreement (d)-for all three crops suggested that the model can be used to highly reliably assess yield and IWUE. This conclusion was derived based on low values of RMSE and high values of d (in the case of maize and sugar beet 0.999 for both yield and IWUE, and in the case of sunflower 0.999 for yield and 0.884 for IWUE). It is noteworthy that under wet conditions, the model suggested that sunflower and sugar beet do not require irrigation, as confirmed by experimental research. These data are significant because they show that the AquaCrop model can be used in impartial decision-making and in the selection of crops to be given irrigation priority in areas where water resources are limited.

Growing water scarcity and increasing demands for agricultural products generate much debate about improving the agricultural sector&#x27;s water use efficiency and productivity. Agricultural engineering traditions feed this debate with notions such as agricultural yield gaps and low water use efficiencies that draw attention to potential improvements. However, when perspectives are shifted from an irrigated field to a river basin, someone&#x27;s

The purpose of this study is to obtain a better understanding of groundwater contamination processes in an arid environment (precipitation of 50 mm/year) due to cultivation. Additional aims were to study the fate of N, K, and other ions along the whole hydrological system including the soil and vadose zone, and to compare groundwater in its natural state with contaminated groundwater (through the drilling of several wells).

Crop consumptive water use and productivity are key elements to understand basin water management performance. This article presents a simplified approach to map rice (Oryza sativa L.) water consumption, yield, and water productivity (WP) in the Indo-Gangetic Basin (IGB) by combining remotely sensed imagery, national census and meteorological data. The statistical rice cropped area and production data were synthesized to calculate district-level land productivity, which is then further extrapolated to pixel-level values using MODIS NDVI product based on a crop dominance map. The water consumption by actual evapotranspiration is estimated with Simplified Surface Energy Balance (SSEB) model taking meteorological data and MODIS land surface temperature products as inputs. WP maps are then generated by dividing the rice productivity map with the seasonal actual evapotranspiration (ET) map. The average rice yields for Pakistan, India, Nepal and Bangladesh in the basin are 2.60, 2.53, 3.54 and 2.75 tons/ha, respectively. The average rice ET is 416 mm, accounting for only 68.2% of potential ET. The average WP of rice is 0.74 kg/m 3 . The WP generally varies with the trends of yield variation. A comparative analysis of ET, yield, rainfall and WP maps indicates greater scope for improvement of the downstream areas of the Ganges basin. The method proposed is simple, with satisfactory accuracy, and can be easily applied elsewhere. ß

Erosion from furrow irrigated land is a serious problem in southern Idaho and elsewhere in the western United States. High molecular weight anionic Polyacrylamide (a water soluble polymer), increases soil aggregate stability and flocculates suspended sediments, thereby reducing sediment detachment and transport in irrigation furrows. Application of 0.7 kg/ha/irrigation of polyacrylamide in irrigation water has reduced furrow erosion by 85 to 99%. In the present work, sediment movement and infiltration were measured in a recirculating furrow infiltrometer with two polyacrylamide treatments. Mean erosion reduction was 70%. Polyacrylamide increased mean infiltration by 30%, probably the result of reduced sediment movement and furrow surface seal formation. Infiltration was inversely related to maximum sediment concentration in the flowing water for both treated and untreated furrows. Farmers who use polyacrylamide must adapt their irrigation management to the higher infiltration to mai...

As part of the 2006 Climate Change Report to Governor Schwarzenegger and the California Legislature, an application of the Water Evaluation and Planning (WEAP) system in the Sacramento River Basin was deployed to look at the impact of climate change on agricultural water management and the potential for adaptation. The WEAP system includes a dynamically integrated rainfall runoff hydrology module that generates the components of the hydrologic cycle from input climate time series. This allows for direct simulation of water management responses to climate change without resorting to perturbations of historically observed hydrologic conditions. In the Sacramento River Basin, the four climate time series adopted for the 2006 Climate Change Report were used to simulate agricultural water management without any adaptation and with adaptation in terms of improvements in irrigation efficiency and shifts in cropping patterns during dry periods. These adaptations resulted in lower overall water demands in the agricultural sector, to levels observed during the recent past, and associated reductions in groundwater pumping and increases in surface water allocations to other water use sectors.

This paper presents the findings of the effect of some selected deficit irrigation scheduling practices on irrigated maize crop in a sub-catchment in south western part of Tanzania. Field experiments, in which maize (TMV1-ST) variety was planted under total irrigation, were conducted during the dry seasons of 2004 and 2005. Surface irrigation method was used and the crop was planted in basins. The seasonal water applied ranged from 400 to 750 mm. Soil moisture content from both cropped and bare soils, leaf area index, dry matter, and grain yields were measured. The dry matter yield ranged between 6,966 and 12,672 kg/ha, and grain yields obtained were between 1,625 and 4,349 kg/ha. The results showed that deficit irrigation at any crop growth stage of the maize crop led to decrease in dry matter and grain yields, seasonal evapotranspiration and deep percolation. Deficit irrigation in any one growth stage of the maize crop only seems to affect grain production and no significant effect on biomass production, but deficit irrigation that spanned across two or more growth stages affect both biomass and grain production drastically. Crop water use efficiency (WUE) and Irrigation water use efficiency (IWUE) were strongly influenced by the number of growth stages in which deficit irrigations were applied and how critical the growth stages were to moisture stress rather than the amount of irrigation water applied. While maximum WUE was obtained under full irrigation, maximum IWUE was obtained in the deficit irrigation treatment at vegetative growth stage, which suggest that IWUE may be improved upon by practicing deficit irrigation at the vegetative growth stage of the maize crop.

Experiments were conducted in summer of 2003 and 2004 to study the effect of withholding irrigation on tomato growth and yield in a drip irrigated, plasticulture system. Irrigation treatments were initiated at tomato planting (S0), after transplant establishment (S1), at first flower (S2), at first fruit (S3), or at fruit ripening (S4). An additional treatment received only enough water to apply fertigation (FT). Withholding drip irrigation for a short period (S2–S3) increased tomato marketable yield by 8–15%, fruit number by 12–14% while reducing amount of irrigation water by 20% compared to the S0 treatment. Withholding drip irrigation also increased irrigation water use efficiency (IWUE). Similar trends were observed in 2003 and 2004 despite large differences in rainfall, heat units, and tomato yield between years. This suggests that if soil moisture is adequate at transplanting, subsequent withholding of irrigation for 1–2 weeks after tomato transplanting may increase yield while reducing the amount of irrigation water.

Crop irrigation uses more than 70% of the world's water, and thus, improving irrigation efficiency is decisive to sustain the food demand from a fast-growing world population. This objective may be accomplished by cultivating more water-efficient crop species and/or through the application of efficient irrigation systems, which includes the implementation of a suitable method for precise scheduling. At the farm level, irrigation is generally scheduled based on the grower's experience or on the determination of soil water balance (weather-based method). An alternative approach entails the measurement of soil water status. Expensive and sophisticated root zone sensors (RZS), such as neutron probes, are available for the use of soil and plant scientists, while cheap and practical devices are needed for irrigation management in commercial crops. The paper illustrates the main features of RZS' (for both soil moisture and salinity) marketed for the irrigation industry and discusses how such sensors may be integrated in a wireless network for computercontrolled irrigation and used for innovative irrigation strategies, such as deficit or dual-

The purpose of this work is to contribute to the development of a combined approach to evaluate irrigated areas based on: (1) irrigation performance analysis intended to assess the productive impacts of irrigation practices and infrastructures, and (2) water accounting focused on the hydrological impacts of water use. Ador-Simulation, a combined model that simulates irrigation, water delivery, and crop growth and production was applied in a surface irrigated area (1213 ha) located in the Bear River Irrigation Project, Utah, U.S.A.. A soil survey, a campaign of on-farm irrigation evaluations and an analysis of the database from the Bear River Canal Company and other resources were performed in order to obtain the data required to simulate the water flows of the study area in 2008. Net land productivity (581 US$ ha −1 ) was 20% lower than the potential value, whereas on-farm irrigation efficiency (IE) averaged only 60%. According to the water accounting, water use amounted to 14.24 Mm 3 , 86% of which was consumed through evapotranspiration or otherwise non-recoverable. Gross water productivity over depleted water reached 0.132 US$ m −3 . In addition, two strategies for increasing farm productivity were analyzed. These strategies intended to improve water management and infrastructures raised on-farm IE to 90% reducing the gap between current and potential productivities by about 50%. Water diverted to the project was reduced by 2.64 Mm 3 . An analysis based on IE could lead to think that this volume would be saved. However, the water accounting showed that actually only 0.91 Mm 3 would be available for alternative uses. These results provide insights to support the decision-making processes of farmers, water user associations, river basin authorities and policy makers. Water accounting overcomes the limitations and hydrological misunderstandings of traditional analysis based on irrigation efficiency to assess irrigated areas in the context of water scarcity and competitive agricultural markets.

Years of ill-managed irrigation have triggered secondary soil salinization in the Khorezm region of Uzbekistan located in the Aral Sea basin. To assess the magnitude and dynamics of secondary soil salinization, to quantify improved management strategies and to derive updated irrigation standards, the soil water model Hydrus-1D was used. Water and soil salinity dynamics in three cotton fields with different soil textures were monitored and simulated for the years 2003 and 2005. Until now in Khorezm, overall soil salinity could only be controlled by pre-season salt leaching using high amounts of water. This water, however, may not be available anymore in the near future because of global climate change and shrinking fresh water resources. Simulations confirmed that the present leaching practice is barely effective. At two out of the three locations within a sandy loam field, leaching did not remove salts from the 2 m profile. Instead, salts were only shifted from the upper (0–0.8 m) to the lower (0.8–2 m) soil layer. Strong groundwater contribution to evapotranspiration triggered secondary (re)-salinization of the topsoil during the cropping season. As a consequence, salt amounts in the top 0.8 m of soil increased from 9 to 22 Mg ha−1 in the field with loamy texture, and from 4 to 12 Mg ha−1 in the field with sandy texture. Management strategy analyses revealed that reducing soil evaporation by a surface residue layer would notably decrease secondary soil salinization. Here, owing to the reduced capillary rise of groundwater, post-season salt contents of the three fields were reduced by between 12 and 19% when compared with residue-free conditions. Even more effective would be improving the efficiency of the drainage system so as to lower the groundwater table. This would require a revision of the current irrigation management schemes, but could, as simulations revealed, reduce the post-season salt content in the 2 m soil profile of the three fields by between 36 and 59% when compared with unaltered conditions. For the revised irrigation management in total not more water than already foreseen by national irrigation recommendations would be needed. Increasing leaching and irrigation efficiency would help sustaining the present cotton production levels while reducing future leaching demands.

Most trickle irrigation in the world is surface drip yet subsurface drip irrigation (SDI) can substantially improve irrigation water use efficiency (IWUE) by minimizing evaporative loss and maximizing capture of in-season rainfall by the soil profile. However, SDI emitters are placed at depths, and in many soil types sustained wetting fronts are created that lead to hypoxia of the rhizosphere, which is detrimental to effective plant functioning. Oxygation (aerated irrigation water) can ameliorate hypoxia of SDI crops and realize the full benefit of SDI systems. Oxygation effects on yield, WUE and rooting patterns of soybean, chickpeas, and pumpkin in glasshouse and field trials with SDI at different emitter depths (5, 15, 25, and 35 cm) were evaluated. The effect of oxygation was prominent with increasing emitter depths due to the alleviation of hypoxia. The effect of oxygation on yield in the shallow-rooted crop vegetable soybean was greatest (+43%), and moderate on medium (chickpea +11%) and deep-rooted crops (pumpkin +15%). Oxygation invariably increased season-long WUE (WUEsl) for fruit and biomass yield and instantaneous leaf transpiration rate. In general, the beneficial effects of oxygation at greater SDI depth on a heavy clay soil were mediated through greater root activity, as observed by general increase in root weight, root length density, and soil respiration in the trialed species. Our data show increased moisture content at depth with a lower soil oxygen concentration causing hypoxia. Oxygation offsets to a degree the negative effect of deep emitter placement on yield and WUE of SDI crops.

Drip irrigation figures prominently in water policy debates as a possible solution to water scarcity prob-lems, based on the assertion that it will improve water use efficiencies. We use this article to carefullytrace the scientific basis of this assertion. Through a systematic review of the literature, we show thatthe term efficiency means different things to different people, and can refer to different elements in thewater balance. Most articles claim that drip irrigation is irrigation water use efficient and crop water useefficient, but different studies use different definitions of these terms. In addition, measured efficiencygains not only refer to different capacities of the technology, but are also based on very specific boundary(scale) assumptions. We conclude that efficiency gains from drip irrigation will only be achieved undernarrowly defined operational conditions, and just apply to very specific spatial and temporal scales.Hence, and unlike what generalized statements in policy documents and the overall enthusiasm for dripas a water saving tool suggest, expectations of increased water efficiencies associated with drip will onlybe realized, and are just realizable, in very specific circumstances.

A study was conducted to determine the effects of different drip irrigation regimes on yield and yield components of cucumber (Cucumbis sativus L.) and to determine a threshold value for crop water stress index (CWSI) based on irrigation programming. Four different irrigation treatments as 50 (T-50), 75 (T-75), 100 (T-100) and 125% (T-125) of irrigation water applied/cumulative pan evaporation (IW/CPE) ratio with 3-day-period were studied.

The potato (Solanum tuberosum L.) is widely planted in the Middle Anatolian Region, especially in the Nigde-Nevsehir district where 25% of the total potato growing area is located and produces 44% of the total yield. In recent years, the farmers in the Nigde-Nevsehir district have been applying high amounts of nitrogen (N) fertilizers (sometimes more than 900 kg N ha À1) and frequent irrigation at high rates in order to get a much higher yield. This situation results in increased irrigation and fertilization costs as well as polluted ground water resources and soil. Thus, it is critical to know the water and nitrogen requirements of the crop, as well as how to improve irrigation efficiency. Field experiments were conducted in the Nigde-Nevsehir (arid) region on a Fluvents (Entisols) soil to determine water and nitrogen requirements of potato crops under sprinkler and trickle irrigation methods. Irrigation treatments were based on Class A pan evaporation and nitrogen levels were formed with different nitrogen concentrations. The highest yield, averaging 47,505 kg ha À1 , was measured in sprinkler-irrigated plots at the 60 g m À3 nitrogen concentration level in the irrigation treatment with limited irrigation (480 mm). Statistically higher tuber yields were obtained at the 45 and 60 g m À3 nitrogen concentration levels in irrigation treatments with full and limited irrigation. Maximum yields were obtained with about 17% less water in the sprinkler method as compared to the trickle method (not statistically significant).

Irrigation scheduling based on the daily historical crop evapotranspiration (ETh) data was theoretically and experimentally assessed for the major soil-grown greenhouse horticultural crops on the Almería coast in order to improve irrigation efficiency. Overall, the simulated seasonal ETh values for different crop cycles from 41 greenhouses were not significantly different from the corresponding values of real-time crop evapotranspiration (ETc). Additionally, for the main greenhouse crops on the Almería coast, the simulated values of the maximum cumulative soil water deficit in each of the 15 consecutive growth cycles (1988–2002) were determined using simple soil-water balances comparing daily ETh and ETc values to schedule irrigation. In most cases, no soil-water deficits affecting greenhouse crop productivity were detected, but the few cases found led us to also assess experimentally the use of ETh for irrigation scheduling of greenhouse horticultural crops. The response of five greenhouse crops to water applications scheduled with daily estimates of ETh and ETc was evaluated in a typical enarenado soil. In tomato, fruit yield did not differ statistically between irrigation treatments, but the spring green bean irrigated using the ETh data presented lower yield than that irrigated using the ETc data. In the remaining experiments, the irrigation-management method based on ETh data was modified to consider the standard deviation of the inter-annual greenhouse reference ET. No differences between irrigation treatments were found for productivity of pepper, zucchini and melon crops.

A total of five borehole samples were collected from five towns in Owerri metropolis, South-eastern Nigeria and subjected to physio-chemical analysis using atomic absorption spectrophotometer (AAS) and other standard equipment with the aim of characterizing and analysing the groundwater quality indicators. These quality indicators are namely: pH, temperature, total hardness, turbidity, electrical conductivity, total dissolved solids, total suspended solids, dissolved oxygen, Ca2+, Mg2+, Na+, K+, HCO3-, SO42-, Cl-, NO3-, Fe2+, Zn2+, Pb2+, Cu2+, Mn2+, and Cr2+. With the aid of geochemical diagrams acquired using Aquachem 2014.2, we classified the groundwater samples into their respective hydrogeochemical facies, identified their relative similarity and demonstrated the irrigability of the groundwater. The results showed that the groundwater quality indicators occur in the groundwater in amounts that fall within their respective permissible limits as set by World Health Organization (WHO) Drinking Water Standard, and therefore ascertained the groundwater portable and suitable for drinking. The pH of the groundwater has a mean value of 6.7 with a standard deviation of 0.26. The relative abundance of the majority of cations follows this sequence - Na+ > Ca2+ > K+ > Mg2+, while that of the anions follow this sequence - HCO3- > Cl- > SO42- > NO3-. Heavy metals constituents of the groundwater follow this order of relative abundance - Zn2+ > Fe2+ > Mn2+ > Cu2+ > Cr2+ > Pb2+. Three hydrogeochemical facies were identified in the area and they are: the Na+—Cl- water type, the Mixed Ca2+-Na+-HCO3- water type and the Ca2+-Mg2+-HCO3- water type. Great similarities were identified between the geochemical composition of the samples and they are all evidently suitable for irrigation purposes. The TDS level and concentration of Ca2+, Mg2+ and Cl- demonstrated the freshness and softness of the groundwater, with no laxative effects. From series of computations and plots, silicate weathering and seawater intrusion were deduced to be the dominant factors controlling the groundwater chemistry, though there is evidence of poor rock dissolution – immature water-rock equilibrium.

Gaura lindheimeri Engelm. & Gray ‘Siskiyou Pink’ (gaura) and Phlox paniculata L. ‘David’ (garden phlox) were grown for 5 weeks in substrates irrigated at volumetric water contents (Θ) of 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, or 0.45 m3·m−3 using a capacitance sensor-controlled irrigation system. Volumetric water contents of the substrate measured by the capacitance sensors controlling irrigation were correlated with measurements with a separate handheld meter (r 2 = 0.83) and with volumetric water content set points throughout the study (r 2 &gt; 0.98). Only 3.8 (at an irrigation set point of 0.10 m3·m−3) to 53 L (0.45 m3·m−3) of water was used to irrigate gaura and phlox and 0 to 7.74 L of this water leached out of the substrates. Significant leaching occurred only at Θ set points of 0.40, or 0.45 m3·m−3. Gaura had shorter and fewer branches and reduced dry weight when grown at lower volumetric water contents, but plants irrigated at set points above 0.25 m3·m−3 were large enou...

High-frequency drip irrigation supplies water and nutrients at a rate that is close to plant uptake, thus enhancing growth and production. In light of water scarcity in arid regions, marginal water is increasingly considered as a resource for agricultural production. The objective of this study was to investigate the combined effects of pulsed irrigation and water salinity on the response of the soil-plant system. As a test crop, bell pepper (Capsicum annuum L.) was cultivated in a screenhouse and drip irrigated daily (D) and at high frequency (P) with saline (S) and fresh (F) water. Simultaneous monitoring of meteorological, physiological, soil physical, plant and soil chemical, and yield data was performed during the experiment. Most physiological parameters were negatively affected by high water salinity. No consistent effect of the irrigation frequency was found on the overall season, although pulsed irrigation led to higher plant weight and leaf area at the early stages of plant growth. The distinct patterns of soil water content for the two irrigation frequencies are presented. Salinity in the root zone was higher under pulsed irrigation, an observation that is supported by measured leaf chloride content and tensiometer readings indicating that the once daily application may have more efficiently removed salts from the top soil. Yield, fruit weight, and irrigation water use efficiency (IWUE) were highest under once daily irrigation with fresh water. High-frequency irrigation led to higher Mn concentrations in leaves and fruits and increased concentrations of Cl, N, and P in leaves, confirming earlier conclusions on improved P mobilization and uptake under pulsed irrigation.

Improvements in irrigation management are urgently needed in regions where water resources for irrigation are being depleted. This paper combines a water balance model with satellite-based remote-sensing estimates of evapotranspiration (ET) to provide accurate irrigation scheduling guidelines for individual fields. The satellitederived ET was used in the daily soil water balance model to improve accuracy of field-by-field ET demands and subsequent field-scale irrigation schedules. The combination of satellite-based ET with daily soil water balance incorporates the advantages of satellite remote-sensing and daily calculation time steps, namely, high spatial resolution and high temporal resolution. The procedure was applied to Genil-Cabra Irrigation Scheme of Spain, where irrigation water supply is often limited by regional drought. Compared with traditional applications of water balance models (i.e. without the satellite-based ET), the combined procedure provided significant improvements in irrigation schedules for both the average condition and when considering field-to-field variability. A 24% reduction in application of water was estimated for cotton if the improved irrigation schedules were followed. Irrigation efficiency calculated using satellite-based ET and actual applied irrigation water helped to identify specific agricultural fields experiencing problems in water management, as well as to estimate general irrigation efficiencies of the scheme by irrigation and crop type. Estimation of field irrigation efficiency ranged from 0.72 for cotton to 0.90 for sugar beet.

Field experiments were conducted for 3 years from 2000 to 2002 to assess proportional crop yield differences obtained under conventional deficit irrigation (CDI) and partial root zone irrigation (PRI) practices, compared with full irrigation (FULL) where plant water requirements were fully met. The experimental crops included vegetables (tomato and pepper), field crops (maize and cotton) and citrus. The fruit yield of greenhouse-grown tomato with FULL irrigation was higher than with PRI (7-22% lower) but was not significantly different. The PRI treatments had 7-10% additional tomato yield over CDI receiving the same amount of water. The yield of pepper, however, decreased in proportion to the level of irrigation deficit with no increase of irrigation water use efficiency (IWUE). No seed yield decrease was evident for cotton with the deficit treatments (PRI and CDI) compared with FULL irrigation. Similarly, the PRI treatment did not give any yield benefit for maize compared with CDI. The ranking of fruit yields of mandarin, FULL > PRI > CDI, was the same as that of other crops; however, the differences were not significant. Although the deficit treatments (PRI and CDI) had as high as 39% increase in IWUE, compared with FULL treatment, some adverse effects on fruit quality were evident such as smaller size of fruits under the deficit treatments.

a g r i c u l t u r a l w a t e r m a n a g e m e n t 9 5 ( 2 0 0 8 ) 9 0 9 -9 1 7 (S. Geerts). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g w a t 0378-3774/$ -see front matter #

Overirrigation of lawns with limited resources of potable water has increasingly become an issue for the state of Florida. A previous study showed that soil moisture sensors systems ͑SMSs͒ could lead to irrigation water savings during relatively wet/normal weather conditions. This research, as a follow-up comparison, was conducted under dry weather conditions. The first objective was to statistically evaluate the water savings potential of different commercially available SMSs during the first half of 2006. In the second half, the objectives were to quantify irrigation water use and to evaluate turfgrass quality differences among: ͑1͒ a time-based irrigation schedule system with and without a rain sensor; ͑2͒ time-based schedules compared to SMS-based systems; and ͑3͒ SMS-based systems under different irrigation frequencies. The experimental area was located in Gainesville, Fla. and consisted of common bermudagrass ͓Cynodon dactylon ͑L.͒ Pers.͔ plots. Four commercially available SMSs ͑brands Acclima, Rain Bird, Irrometer, and Water Watcher͒ were used to bypass scheduled irrigation cycles when the soil water content at the 7-to 10-cm depth was above field capacity. Time-based treatments with and without rain sensor feedback were set up as comparisons for irrigation depth applied, and a nonirrigated treatment for turf quality comparison purposes was implemented. Due to the dry weather conditions and/or infrequent rain events during the experiment, the nonirrigated plots ͑as well as a broken SMS treatment͒ resulted in turfgrass quality below the minimum acceptable level. The rest of the treatments had at least minimum acceptable turf quality. The treatment with rain sensor resulted in 13 to 24% less water applied than without the rain sensor treatment. Most SMS-based treatments resulted in significant irrigation water savings compared to the treatment without rain sensor, which ranged from 16 to 54% in the first half, and from 28 to 83% in the second half of 2006, for three of four SMS brands tested.

The aim of this study carried out in Van, Turkey was to determine the most suitable irrigation frequencies and quantities in summer squash (Cucurbita pepo L. cv. Sakız) grown under field conditions. Irrigation quantities were based on pan evaporation (E pan ) from a screened class-A pan. Irrigation treatments consisted of two irrigation intervals (I1: 5 days; I2: 10 days), and three pan coefficients (K cp 1: 0.45; K cp 2: 0.65 and K cp 3: 0.85). Plants were adequately watered from seed sowing to first fruit emergence, then, scheduled irrigations were initiated at 5-and 10-day intervals.

The response of sunflower (Helianthus annuus L.) to 14 irrigation treatments in a sub-humid environment (Bursa, Turkey) was studied in the field for two seasons. A rainfed (non-irrigated) treatment as the control and 13 irrigation treatments with full and 12 different deficit irrigations were applied to the hybrid Sanbro (Novartis Seed Company) planted on clay soil, at three critical development stages: heading (H), flowering (F) and milk ripening (M). The yield increased with irrigation water amount, and the highest seed yield (3.95 t ha−1) and oil yield (1.78 t ha−1) were obtained from the HFM treatment (full irrigation at three stages); 82.9 and 85.4% increases, respectively, compared to the control. Evapotranspiration (ET) increased with increased amounts of irrigation water supplied. The highest seasonal ET (average of 652 mm) was estimated at the HFM treatment. Additionally, yield response factor (k y) was separately calculated for each, two and total growth stages, and k y was found to be 0.8382, 0.9159 (the highest value) and 0.7708 (the lowest value) for the total growing season, heading, and flowering-milk ripening combination stages, respectively. It is concluded that HFM irrigation is the best choice for maximum yield under the local conditions, but these irrigation schemes must be re-considered in areas where water resources are more limited. In the case of more restricted irrigation, the limitation of irrigation water at the flowering period should be avoided; as the highest water use efficiency (WUE) (7.80 kg ha−1 mm−1) and irrigation water use efficiency (IWUE) (10.19 kg ha−1 mm−1) were obtained from the F treatment.

M. Rinaldi), domenico.ventrella@entecra.it (D. Ventrella), caterina.gagliano@entecra.it (C. Gagliano). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a g w a t 0378-3774/$ -see front matter #

The use of partial root-drying (PRD) irrigation implies doubling pipelines instead of using a conventional single pipeline. However, pipelines can be spaced a short distance apart (e.g. 1 m) along the vine row ("D" layout) or joined with cable ties and laid as a single pipeline ("S" layout). Pipelines in "S" conWguration are laid under the vine row, and in "D" at both sides of the vine row. These two diVerent layouts can change the wetted soil zone and aVect grapevine response to irrigation. The focus of this study was therefore on establishing the role of pipeline layout in vine-grape (cv. 'Tempranillo') response under semi-arid conditions in which PRD is managed as a deWcit irrigation technique. Six irrigation treatments were applied, which resulted from the combination of Control (C, full irrigation), PRD and seasonal sustained deWcit irrigation (SSDI), and "S" and "D" pipeline layouts. SSDI and PRD were irrigated to 50% C throughout the irrigation season, and C irrigation was scheduled according to a crop water balance technique. Midday stem water potential ( stem ) and leaf conductance (g l ) indicated that, on the whole, PRD treatments had a slightly higher water status than SSDI treatments, but a substantially lower status than C treatments. Use of the "D" pipeline layout signiWcantly reduced stem in both PRD and SSDI treatments and in some instances for Control conditions, too. Berry yield, vine intercepted radia-tion, leaf abscisic acid (ABA) and g l were highly correlated with stem . DiVerences in water status between PRD-S and SSDI-S, according to a sub-surface irrigation test, seemed to be more related to changes in soil evaporation losses and irrigation eYciency than to any intrinsic PRD eVect. PRD-S accounted for water savings equivalent to 10% according to the ratio between applied water and grape production for the SSDI-S treatment, whereas PRD-D berry yield was not signiWcantly diVerent from that associated with the SSDI-S treatment. In conclusion, under the growing conditions of this experiment, PRD-S oVered the possibility of slightly improving water conservation when irrigation was applied to the soil surface.