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1.
Accurate irrigation scheduling is important to ensure maximum yield and optimal water use in irrigated cotton. This study hypothesizes that cotton water stress in relatively humid areas can be detected from crop stress indices derived from canopy reflectance or temperature. Field experiments were conducted in the 2003 and 2004 crop seasons with three irrigation treatments and multiple cultivars to study cotton response to water stress. The experiment plots were monitored for soil water potential (SWP), canopy reflectance and canopy temperature. Four crop stress indices namely normalized difference vegetative index (NDVI), green NDVI (GNDVI), stress time (ST) index and crop water stress index (CWSI) were evaluated for their ability to indicate water stress. These indices were analyzed with classic mixed regression models and spatial regression models for split-plot design. Rainfall was plentiful in both seasons, providing conditions representative of irrigated agriculture in relatively wet regions. Under such wet weather conditions, excessive irrigation decreased lint yield, indicating the necessity for accurate irrigation scheduling. The four crop stress indices showed significant responses to irrigation treatments and strong correlation to SWP at shallow (0.2 m) depth. Spatial regression models were able to accurately explain the effect of irrigation treatment, while classic split-plot ANOVA models were confounded by collinearity in data across space and time. The results also verified that extreme humidity can mask canopy temperature differences with respect to ambient temperature, adding errors to canopy temperature-based stress indicators.
Sreekala G. BajwaEmail:
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2.
Micro-irrigation technologies are promoted for various reasons in India. Despite the reported significant economic advantages, and the concerted support of the government and NGOs, the current micro-irrigation area in India remains an insignificant proportion of its potential. This paper analyzes: (1) the economics of alternative micro-irrigation technologies, (2) the determinants of adoption, (3) the poverty outreach of the different micro-irrigation systems, and (4) the sustainability implications of micro-irrigation adoption. In line with the findings of other studies, this study indicates that micro-irrigation technologies result in a significant productivity and economic gains. The most important determinants of micro-irrigation adoption include access to groundwater, cropping pattern, availability of cash, and level of education, the social status and poverty status of the farmer. Contrary to the expectations, the majority of the current adopters of low-cost micro-irrigation systems are the better-off farmers. The study indicates that the impact of micro-irrigation systems on the sustainability of groundwater resources depends upon the magnitude of the overall productivity gain following the shift from traditional irrigation method to micro-irrigation system, the pattern of use of the saved water, and the type and potential number of adopters. This study was supported by the Comprehensive Assessment of Water Management in Agriculture (CA) and IWMI-TATA Water Policy Program.
R. E. NamaraEmail:
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3.
In this study, six extrapolation methods have been compared for their ability to estimate daily crop evapotranspiration (ETd) from instantaneous latent heat flux estimates derived from digital airborne multispectral remote sensing imagery. Data used in this study were collected during an experiment on corn and soybean fields, covering an area of approximately 12 × 22 km, near Ames, Iowa. ETd estimation errors for all six methods and both crops varied from −5.7 ± 4.8% (MBE ± RMSE) to 26.0 ± 15.8%. Extrapolated ETd values based on the evaporative fraction (EF) method better compared to eddy covariance measured ET values. This method reported an average corn ETd estimate error of −0.3 mm day−1, with a corresponding error standard deviation of 0.2 mm day−1, i.e., about 5.7 ± 4.8% average under prediction when compared to average ETd values derived from eddy covariance energy balance systems. A solar radiation-based ET extrapolation method performed relatively well with ETd estimation error of 2.2 ± 10.1% for both crops. An alfalfa reference ET-based extrapolation fraction method (ETrF) yielded an overall ETd overestimation of about 4.0 ± 10.0% for both crops. It is recommended that the average daily soil heat flux not be neglected in the calculation of ETd when utilizing method EF. These results validate the use of the airborne multispectral RS-based ET methodology for the estimation of instantaneous ET and its extrapolation to ETd. In addition, all methods need to be further tested under a variety of vegetation surface homogeneity, crop growth stage, environmental and climatological conditions.
José L. Chávez (Corresponding author)Email:
Christopher M. U. NealeEmail:
John H. PruegerEmail:
William P. KustasEmail:
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4.
Ethiopia’s irrigation potential is estimated at 3.7 million hectare, of which only about 190,000 ha (4.3% of the potential) is actually irrigated. There is little information on the extent to which the so far developed irrigation schemes have been effective in meeting their stated objectives of attaining food self-sufficiency and eradicating poverty. Therefore, the aim of this paper is to identify the impact of small-scale irrigation on household food security based on data obtained from 200 farmers in Ada Liben district of Ethiopia in 2006. The resulting data was analyzed using Heckman’s Two-step Estimation procedure. Studies elsewhere revealed that access to reliable irrigation water can enable farmers to adopt new technologies and intensify cultivation, leading to increased productivity, overall higher production, and greater returns from farming. Our study findings confirm some of these claims. In the study area about 70% of the irrigation users are food secure while only 20% of the non-users are found to be food secure. Access to small scale irrigation enabled the sample households to grow crops more than once a year; to insure increased and stable production, income and consumption; and improve their food security status. The study concludes that small-scale irrigation significantly contributed to household food security.
Dereje BachaEmail:
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5.
This paper provides an overview of the issues in and approaches to measuring and enhancing the value of agricultural water in large irrigated river basins. It develops a framework and a set of indicators for valuing agricultural water by looking into various dimensions and underlying key factors that influence the value of water at micro, meso and macro levels. The indicators are applied to recent, primary- and secondary-level empirical data from the Indus basin Irrigation system of Pakistan. In addition, the paper compiles recent estimates of the value of agricultural water from 40 settings in 23 countries. Finally, the paper outlines measures for enhancing the value of agricultural water. The paper makes four main points: (1) The popular productivity indicators based on crop output do not capture the full range of benefits and costs associated with agricultural water use. (2) The value of agricultural water may not be as low as it is generally perceived or estimated when all major uses and direct and indirect benefits of water at various levels are properly accounted for. (3) The value of water varies across time and space, and the value to stakeholders at various scales (farmer, system manager, basin planner and national policy maker) could be quite different. For example, the estimate of agricultural water value in the upper Indus basin in Pakistan varies from US$0.04/m3 at the farm scale to US$0.22/m3 at the national scale. The farm-scale value is more relevant, e.g., for agricultural water charging policies, but for water-sector investments and allocation decisions, the national-scale value is important. The decision-making processes related to water sector investments, allocations, management, and charging/cost recovery schemes could be potentially misguided if key dimensions of water value that are related to water availability and use, benefits/costs, and temporal and spatial aspects are not properly accounted for in valuation. (4) Efforts should be directed not only at increasing the productivity of water in terms of mass of output per unit of water, but also the overall benefits or value of water at various levels for larger growth and poverty alleviation impacts, considering the sustainability of the systems.
Intizar HussainEmail:
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6.
The system of rice intensification (SRI) developed in Madagascar, is showing that by changing the management of rice plants, soil, water and nutrients it can increase the yields of irrigated rice by 25–50% or more while reducing water requirements by an equivalent percent. This gives farmers incentive to reduce their irrigation water use when growing rice, especially since SRI methods can also reduce farmers’ costs of production which increases their net income ha−1 by even more than yield. Even though these results sound fantastic, the validity of SRI concepts and practices has been demonstrated in more than 20 countries to date. This article considers, first, the methods that make these improvements possible and how these are achieved. It then briefly surveys SRI experience in five Asian countries, incentives in addition to yield, water-saving and profitability for adopting SRI, and possible limitations or disadvantages with the methodology. Next, it comments on the debate over SRI in the agronomic literature and then adds to the empirical record by reporting in some detail on SRI evaluations in two of India’s main rice-growing states, Andhra Pradesh and Tamil Nadu, where water availability is becoming more problematic and where SRI use is spreading. Finally, the article briefly discusses some implications of saving irrigation water by changing resource management rather than by using on more or different inputs.
Norman UphoffEmail:
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7.
Impact of research on water use for irrigation in Israel   总被引：1，自引：1，他引：0  
The decrease of annual irrigation application rate observed since 1950 was reversed in 1988 as a result of a sudden increase of the amount of treated effluents used for irrigation. Intensification of research on irrigation with effluents and marginal water starting in 1994 resulted four years later in the renewal of the decrease of irrigation application rate. Contribution No. 614/06 from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel.
Marcel FuchsEmail:
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8.
As the competition for the finite water resources on earth increases due to growth in population and affluence, agriculture is faced with intensifying pressure to improve the efficiency of water used for food production. The causes for the relatively low water use efficiency in agriculture are numerous and complex, including environmental, biological, engineering, management, social, and economic facets. The complexity of the problem, with its myriads of local variations, requires a comprehensive conceptual framework of the underlying physical and biological processes as the basis to analyze the existing situation and quantify the efficiencies, and to plan and execute improvements. This paper proposes such a framework, based on the simple fact that the overall efficiency of any process consisting of a chain of sequential step is the product of the efficiency (i.e., output/input ratio) of its individual component steps. In most cases of water use, a number of process chains, both branching and merging, are involved. Means to integrate the diverging and converging chains are developed and presented as equations. Upscaling from fields to regions and beyond are discussed. This chain of efficiencies approach is general and can be applied to any process composed of chains of sequential steps. Here the framework is used to analyze the systems of irrigated and dryland crop production, and animal production on rangeland. Range of plausible efficiencies of each step is presented as tables, with values separately for the poor and for the good situation of circumstances, management and technology. Causes of the differences in efficiency of each step, going from water delivery to soil water extraction, transpiration, photosynthesis, and conversion to crop biomass and yield, and to animal product are briefly discussed. Sample calculations are made to demonstrate how modest differences in the efficiencies of the component steps are manifested as large to huge differences in the overall efficiency. Based on an equation quantifying the impact of changes in efficiency of component steps on the overall efficiency, it is concluded that generally, it is more effective to made modest improvements in several or more steps than to concentrate efforts to improve one or two steps. Hence, improvement efforts should be systematic and not overly concentrated on one or two components. The potential use of the same equation as the point of departure to optimize the allocation of economic resource among the component steps to maximize the improvement in the overall water use efficiency is elaborated on. The chain of efficiencies framework provides the means to examine the current levels of efficiency along the pathways of agricultural water use, to analyze where inefficiencies lie by comparing with the range of known efficiency values in the tables presented, to assess the potential improvements that may be achieved in various parts and their impact on the overall efficiency, and to aid in the optimal allocation of resources for improvements.
Theodore C. HsiaoEmail:
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9.
Adoption of more uniform sprinkler systems involves a trade off between increased capital expenditure on equipment and the benefits associated with reduced water application when application is uniform. An empirical analysis of the economics of lettuce production, grown using sprinkler systems under the windy conditions of the Swan Coastal plain in Western Australia is presented, where the yield response to water exhibits eventual declining marginal productivity. A range of sprinkler designs that have been field-tested for performance were examined. The optimal per-crop water application for the least efficient system was up to double the application rate of the most efficient system. However, the economic analysis demonstrates that there are clear incentives for adopting more water-efficient systems despite the higher capital cost, because of the yield depressing effect of over-watering. Sensitivity analysis demonstrates substantially poorer incentives for improving irrigation efficiency when yield relationships follow a Mitscherlich functional form.
Donna BrennanEmail:
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10.
Weighing lysimeters are the standard method for directly measuring evapotranspiration (ET). This paper discusses the construction, installation, and performance of two (1.52 m × 1.52 m × 2.13-m deep) repacked weighing lysimeters for measuring ET of corn and soybean in West Central Nebraska. The cost of constructing and installing each lysimeter was approximately US $12,500, which could vary depending on the availability and cost of equipment and labor. The resolution of the lysimeters was 0.0001 mV V−1, which was limited by the data processing and storage resolution of the datalogger. This resolution was equivalent to 0.064 and 0.078 mm of ET for the north and south lysimeters, respectively. Since the percent measurement error decreases with the magnitude of the ET measured, this resolution is adequate for measuring ET for daily and longer periods, but not for shorter time steps. This resolution would result in measurement errors of less than 5% for measuring ET values of ≥3 mm, but the percent error rapidly increases for lower ET values. The resolution of the lysimeters could potentially be improved by choosing a datalogger that could process and store data with a higher resolution than the one used in this study.
José O. Payero (Corresponding author)Email:
Suat IrmakEmail:
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11.
Drip irrigation has the potential to save water and mitigate foliar diseases for processing tomato production in Central Brazil. Four experiments were carried out at Embrapa Vegetables, Brasília, Brazil, to establish irrigation management strategies during vegetative, fruit development, and maturation growth stages of drip-irrigated processing tomato. Soil water tension (SWT) threshold values ranging from 5 to 120 kPa were evaluated. Plants growing under higher water deficit during the vegetative stage showed root systems up to 10 cm deeper than those irrigated more frequently. Maximum fruit yield was reached when irrigations were performed at SWT thresholds of 35, 12, and 15 kPa during vegetative, fruit development, and maturation growth stages, respectively. Total soluble solids content was not affected by irrigation treatments during vegetative and fruit development stages, but increased as SWT increased during fruit maturation growth stage.
Waldir  A. MarouelliEmail:
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12.
The paper argues that conventional irrigation design processes rely heavily on predetermined design criteria, often without allowing for interactions with farmers and revising of criteria during implementation. Six cases from a tertiary development project in North Sulawesi, Indonesia are described, where farmers altered what had been designed and constructed by contracting and agency engineers. Through field inspections and farmer interviews, the farmers' alternative set of design criteria was elicited to explain why the farmers changed what had been constructed. A total of 27 cases are analyzed to show the relative importance of:
–  farmer criteria which are compatible with project criteria but which draw on local knowledge of the environment,
–  farmer criteria which were additional to project criteria and
–  farmer criteria which were incompatible with project criteria.
–  Some mechanisms are suggested for how to incorporate into the design process local knowledge, interactive learning and flexibility.
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13.
Irrigation scheduling requires an operational means to quantify plant water stress. Remote sensing may offer quick measurements with regional coverage that cannot be achieved by current ground-based sampling techniques. This study explored the relation between variability in fine-resolution measurements of canopy temperature and crop water stress in cotton fields in Central Arizona, USA. By using both measurements and simulation models, this analysis compared the standard deviation of the canopy temperature to the more complex and data intensive crop water stress index (CWSI). For low water stress, field was used to quantify water deficit with some confidence. For moderately stressed crops, the was very sensitive to variations in plant water stress and had a linear relation with field-scale CWSI. For highly stressed crops, the estimation of water stress from is not recommended. For all applications of one must account for variations in irrigation uniformity, field root zone water holding capacity, meteorological conditions and spatial resolution of T c data. These sensitivities limit the operational application of for irrigation scheduling. On the other hand, was most sensitive to water stress in the range in which most irrigation decisions are made, thus, with some consideration of daily meteorological conditions, could provide a relative measure of temporal variations in root zone water availability. For large irrigation districts, this may be an economical option for minimizing water use and maximizing crop yield.
M. P. González-DugoEmail: Phone: +34-957-016030Fax: +34-957-016043
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14.
A subsurface drip irrigation study with cotton used canopy temperature to determine signals for irrigation control during 2002–2004. Timing of irrigation applications was controlled by the biologically identified optimal temperature interactive console (BIOTIC) protocol, which used stress time (ST) and a crop-specific optimum temperature to indicate water stress. ST was the cumulative daily time quantity when cotton canopy temperature exceeded 28°C. STs between 5.5 and 8.5 h in 1 h increments were irrigation signal criteria, which produced different irrigation regimes. This investigation examined the association among ST, daily average canopy temperature (T c), canopy and air temperature difference (T c−T a), and the relative crop water stress index (RCWSI) including their relationship with lint yield. Number of irrigation signals decreased linearly with ST at the rate of −10.2 and −8.7 irrigations per 1 h increase of ST in 2003 and 2004. There were significant curvilinear relationships between ST and the average daily stress on days with irrigation signals and for days without irrigation signals across years. The percentage of positive daily (T c−T a) values increased with ST level. ST and T c were positively related in all irrigation signal treatments with 5.5 and 6.5 h being significant in 2003 and 2004. Yield declined at the rate of 343 kg lint/ha for each 1 h increase of ST for days with irrigation signals. ST, mathematically the most simple of the canopy temperature-based parameters, provided the most consistent estimate of crop water stress and correlation with lint yield. The power of ST to characterize water stress effects on crop productivity evolves from being an integrated value of time while canopy temperature exceeds a physiologically based threshold value.
D. F. WanjuraEmail: Phone: +1-806-7235241Fax: +1-806-7235272
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15.
A drip-irrigation module was developed and included in an ecosystem model and tested on two independent datasets, spring and autumn, on field-grown tomato. Simulated soil evaporation correlated well with measurements for spring (2.62 mm d−1 compared to 2.60 mm d−1). Changes in soil water content were less well portrayed by the model (spring r 2 = 0.27; autumn r 2 = 0.45). More independent data is needed for further model testing in combination with developments of the spatial representation of below-ground variables. In a fresh-water drip-irrigated system, about 30% of the incoming water was transpired, 40% was lost as non-productive evaporative flows, and the remainder left the system as surface runoff or drainage. Simulations showed that saline water irrigation (6 dS m−1) caused reduced transpiration, which led to higher drainage and soil evaporation, compared with fresh water. Covering the soil with plastic mulch resulted in an increase in yield and transpiration. Finally, two different drip-irrigation discharge rates (0.2 and 2.5 l h−1) were compared; however the simulations indicated that the discharge rate did not have any impact on the partitioning of the incoming water to the system. The model proved to be a useful tool for evaluating the importance of specific management options.
Louise KarlbergEmail:
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16.
In this paper, an innovative method—that combines a technical and socio-economic analysis—is presented to assess the implications of policy decisions on water productivity. In the technical part, the variability in crop water productivity (CWP) is analyzed on the basis of actual water consumption and associated biomass production using the Surface Energy Balance Algorithm for Land (SEBAL). This generates input for the socio-economic analysis, which aims to quantify the foregone economic water productivity (EWP) of policy decisions to allocate water in a social optimal way. The basis for arguments to transfer water between categories of users will be strengthened and be more objective when the productivity in existing and alternative uses is known. The usefulness of such an approach is shown in the South African part of the Inkomati Basin, where according to the Water Act, water has to be reserved for basic human needs and to protect aquatic ecosystems. The opportunity costs, in terms of foregone EWP, of decisions to divert water away from agriculture are assessed. The results show that diverting water away from crops with a low CWP is not always the most cost-effective way in terms of foregone EWP. This paper is written in the framework of ‘A demonstration project in the Inkomati Basin’ (Soppe et al. 2006) funded by the ‘Partners for Water II’ program of the Dutch government.
P. J. G. J. HellegersEmail:
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17.
The spatial and temporal pattern of root water uptake in partially wetted soil was studied in the root zone of a 6-year-old microsprinkler-irrigated almond tree. The water balance of about one quarter of the root zone’s wetted soil volume (2.0×2.0×0.9 m3) was determined by catch cans, neutron probe and tensiometer measurements. Twenty-five neutron probe access tubes with catch cans were distributed in a square grid of 50 cm spacing. Eight pairs of tensiometers were installed at depths of 82.5 and 97.5 cm in a regular pattern between the access tubes. Neutron probe readings at 15 cm depth increments and tensiometer readings were taken at time intervals of 4–24 h. The rate of soil water depletion was calculated and used to estimate the spatial and temporal distributions of root water uptake. Soil water dynamics was studied in two stages: (1) during a week of conventional irrigation management with three irrigation events; and (2) during a period of 16 days without irrigation, after the monitored soil volume was thoroughly moistened so that soil water was easily available everywhere, initially. The zones of maximum root water uptake were the same for both stages in periods of high local rates of water application. After water applications, root water uptake occurred initially near the tree trunk and then progressed towards the root system periphery, thereby changing locations of maximum root water uptake and shifting to root zone regions with minimum soil water stress.
Kouman S. KoumanovEmail: Phone: +359-32-692349Fax: +359-32-670808
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18.
Real-time information on salinity levels and transport of fertilizers are generally missing from soil profile knowledge bases. A dual-frequency multisensor capacitance probe (MCP) is now commercially available, for sandy soils, to simultaneously monitor volumetric soil water content (VWC) measured as a percentage and salinity as a unitless volumetric ion content (VIC). The objectives of this research were to assess the relationship of salinity and water content with these dual-frequency MCPs under laboratory conditions, and assess its potential for field use in sandy soils of the mid-Atlantic region of the US. Water and salinity studies were conducted in two sand-filled PVC columns, 1.2 m long by 0.25 m ID. Each column was instrumented with ten dual-frequency capacitance sensors and two thermocouple temperature sensors. Four salinity levels were studied in the two columns using 0.5, 1, 2, and 4 dSm−1 NH4NO3 solutions. Water, salinity, and temperature readings were continuously recorded at 1-min intervals. The VIC values were found to be primarily qualitative, but combined with real-time VWC measures the probe could still be an important fertigation management tool to provide near-continuous real-time information on fertilizer penetration, spread and subsequent changes during crop growth.
J. L. StarrEmail:
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19.
Empirical functions for dependent variables in cutback furrow irrigation   总被引：1，自引：0，他引：1  
Water scarcity and the high consumption of water resources in agriculture have strengthened the need to manage and optimize irrigation systems. Among surface irrigation systems, furrow irrigation with cutback is commonly used because of its potentially higher irrigation efficiency, lower costs and relative simplicity. The performance of this system is affected by various management and design variables, and hence different management scenarios should be evaluated before it is applied in practice. For this purpose, empirical functions for the performance evaluation indices are useful. This paper employs sensitivity, dimensional and regression analyses in the development of empirical functions for application efficiency, deep percolation, runoff and distribution uniformity. The proposed functions were evaluated using a numerical zero-inertia model and field measured data. Coefficients of determination for E a, D r, R r and U cc were calculated to be 0.90, 0.91, 0.90 and 0.84, respectively. These values indicate that the proposed functions enable the performance indices to be predicted satisfactorily. Values for the indices calculated using the developed dimensionless functions showed a very good agreement with both the outputs of the zero-inertia model and values calculated from measured field data. As the functions were general (not site and irrigation specific) and explicit, they could prove to be of practical significance in both conventional and optimal design and management of free-draining, graded furrow irrigation systems with cutback flows.
M. NavabianEmail:
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20.
Chloride mass balance (steady state or transient state) models are used extensively in Vertisols of Queensland and New South Wales (NSW) in Australia to estimate deep drainage. The aim of this study was to compare deep drainage estimated assuming steady state and transient state conditions with chloride mass balance models in irrigated cotton (Gossypium hirsutum L.)-based farming systems in the lower Namoi Valley of North Western NSW. Drainage was estimated at seven sites, and treatments included rotation crops such as wheat (21–62 mm/year) (Triticum aestivum), sorghum (12–47 mm/year) (Sorghum bicolor) and dolichos (12–21 mm/year) (Lablab purpureus), minimum tillage (62–83 mm/year), where cotton was sown into standing wheat stubble, and conventional tillage where stubble was incorporated (35–78 mm/year). Soil water content was measured with a neutron moisture meter in the 0.2–1.2 m depth. Soil was sampled before sowing and after harvest to a depth of 1.2 m along diagonal transects. The soil chloride concentration was determined by titration with AgNO3. Irrigation water was also analysed for chloride. The deep drainage estimates were compared using regression analysis and students paired t-test. In addition, a paired t-test of the soil chloride concentration before sowing and after harvest was used to determine if the soil chloride flux was either in a steady state or transient state. In 9 out of the 13 data sets (69%), drainage estimated with the models agreed with changes between pre- and post-season soil chloride concentrations. Under frequently irrigated summer crops such as cotton and sorghum and in better structured soils chloride flux reached steady state conditions whereas under partially-irrigated crops or where soil structure was poorer, the chloride flux deviated markedly from steady-state conditions. The latter observation may be due to preferential flow via deep cracks in infrequently irrigated soil. Deep cracking would be due to the more intense shrinking and swelling in partially irrigated soil in comparison with frequently-irrigated crops. Comparison of estimated deep drainage with pre- and post-season soil chloride concentrations showed that the steady state mass balance model best estimated deep drainage under cotton crops which were irrigated more frequently or wheat crops which had better soil structure.
T. B. WeaverEmail: Phone: +61-2-67991570Fax: +61-2-67991503
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