Farm-level and district efforts to improve water management during drought

The fifth year of drought in California brought reductions in surface water deliveries to many water districts. In the central San Joaquin Valley, water deliveries to Broadview Water District were reduced by 50% in 1990 and by 75% in 1991. The district increased the level of service provided to farmers during these years by providing accurate water use data, increasing the flexibility allowed in scheduling water deliveries, and managing water transfers and purchases when water was available. Farmers in the district implemented new irrigation practices and increased the efficiency of water applications. Several crops were irrigated more frequently than usual, but the amount of water applied during each irrigation event was reduced. The total amount applied during pre-irrigations and seasonal irrigations was also reduced. More than 38% of district land was idled in 1991, with the largest proportional reductions in melon, sugarbeet, and grain plantings. Field application efficiencies increased for all crops in 1990 and 1991 and the district-wide field application efficiency increased from 0.73 in 1989, to 0.77 in 1990, and 0.81 in 1991.     

Farm salinity appraisal with water reuse

The need for a better understanding of the interaction between irrigation practices and the elevation and quality of the water table is of paramount importance for developing irrigation management strategies to ameliorate the regional problems of elevated saline water tables in the San Joaquin Valley, California. An area of approximately 3000 ha which includes portions of the Diener Ranch and the adjacent University of California, Westside Research and Extension Center, located south of Five Points in the Westlands Water District on the west side of the San Joaquin Valley was chosen for extensive field measurements. Field work consisted of four main activities namely, field instrumentation, collection of records of field activities, periodic data collection, and analyses of field data. Field measurements of water table carried out during 1994 indicated that the water table elevation was sensitive to the irrigation practices. There was a general increase in the area with a water table close to the surface during the irrigation season, and a return to water table elevations similar to the starting conditions at the end of the season. During the study period, the surface water quality deteriorated more in areas irrigated with reuse water and persisted through the end of the season. Depth averaged electrical conductivity for the study area over 6.5 m decreased between December 1993 and December 1994. Vertical hydraulic gradients in the saturated zone, were found to be an order of magnitude larger than horizontal gradients. The direction of vertical gradients changed, with downward gradients following pre-irrigations and upward gradients later in the season, when crop water requirements increased. Based on the results of the field study, it can be concluded that the irrigation management practices have a direct effect on local water table response as well as on water quality. Therefore, irrigation practices that promote less deep percolation losses may be helpful in controlling the water table rise.     

Salinity, drainage and selenium problems in the Western San Joaquin Valley of California

Highly productive, irrigated agriculturecan be found in California's Central Valleymade up of the Sacramento, San Joaquin, andTulare Lake basins. High water tablesthroughout much of the San Joaquin andTulare Lake portions of the Valley threatenthis highly productive region. Due totopographic and environmental constraintsmuch of the region is currently withoutdrainage. In 1990 State and Federalgovernment agencies combined to produce areport that outlined possible steps to dealwith the drainage issue. These stepsincluded: 1) Source control (practices toreduce the amount of drainage water); 2)Drainage reuse; 3) Evaporation systems; 4)Land retirement (cease irrigation); 5)Groundwater management; and 6) Discharge tothe San Joaquin River. General backgroundinformation to the history and hydrology ofthe Valley as well as a discussion of thefeasibility and constraints of providingdrainage by discharging drain water to theSan Joaquin River are presented. Inaddition a general discussion of thetechnical and political limitations ofproviding drainage in the River arediscussed.     

Identifying sources of recharge to shallow aquifers using a groundwater model

The poor water quality of sub-surface drainage, hereafter drainage, water generated in the western San Joaquin Valley in California creates management challenges for farmers and water managers. Elevated concentrations of salt and trace elements in agricultural drainage limit the disposal options. In this constrained environment, determining the original source of drainage water is a crucial step in developing appropriate drainage management policies. Numerical modeling results of near-surface water-table fluctuations indicate that the substantial groundwater rise observed in the vicinity of the region's major water supply canal could not be attributed solely to seepage from overlying irrigated fields. An inverse solution approach is used herein to test the theory that seepage from the canal itself and/or that from surface water retention ponds (designed to protect the structure from flash floods) is responsible for an accentuated groundwater mound. The results suggest that canal seepage is the more likely source of non-agricultural aquifer recharge.     

Evaluating the Impact of Irrigation and Drainage Policies on Agricultural Sustainability

Farmers in the Broadview Water District in central Californiahave been improving irrigation practices in response to risingirrigation water prices and reductions in water supply since1989, when incentive policies were first implemented to reducethe volume of subsurface drain water generated in theDistrict. The average salinity of water deliveries hasincreased, over time, as the District has recycled largeamounts of drainage water to achieve regional restrictions ondrainage water discharge. We review irrigation and drainageactivities in Broadview since 1986 with an emphasis on thesustainability of crop production when drainage discharge islimited. Average cotton yields in Broadview have declined inrecent years, both nominally and in comparison with averageyields reported for the large county in which Broadview islocated. Average tomato yields in Broadview have increased inrecent years, but county-wide yields have exceeded Broadviewyields with greater frequency than in the late 1980s. Theseobservations suggest that average crop yields in Broadview maybe starting to reflect the increasing salinity of soil andwater resources, which may be due in part to persistentrestrictions on drainage water discharge.     

Changes in spatial and temporal variability of SAR affected by shallow groundwater management of an irrigated field, California

In the irrigated western U.S. disposal of drainage water has become a significant economic and environmental liability. Development of irrigation water management practices that reduce drainage water volumes is essential. One strategy combines restricted drainage outflow (by plugging the drains) with deficit irrigation to maximize shallow groundwater consumption by crops, thus reducing drainage that needs disposal. This approach is not without potential pitfalls; upward movement of groundwater in response to crop water uptake may increase salt and sodium concentrations in the root zone. The purposes for this study were: to observe changes in the spatial and temporal distributions of SAR (sodium adsorption ratio) and salt in a field managed to minimize drainage discharge; to determine if in situ drainage reduction strategy affects SAR distribution in the soil profile; and to identify soil or management factors that can help explain field wide variability. We measured SAR, soil salinity (EC_1:1) and soil texture over 3 years in a 60-ha irrigated field on the west side of the San Joaquin Valley, California. At the time we started our measurements, the field was beginning to be managed according to a shallow groundwater/drainage reduction strategy. Soil salinity and SAR were found to be highly correlated in the field. The observed spatial and temporal variability in SAR was largely a product of soil textural variations within the field and their associated variations in apparent leaching fraction. During the 3-year study period, the percentage of the field in which the lower profile (90-180 cm) depth averaged SAR was above 10, increased from 20 to 40%. Since salinity was increasing concomitantly with SAR, and because the soil contained gypsum, sodium hazard was not expected to become a limiting factor for long term shallow groundwater management by drain control. It is anticipated that the technology will be viable for future seasons.     

Efficacy of constructed wetlands for removal of bacterial contamination from agricultural return flows

Water quality degradation from bacterial pathogens is one of the leading causes of surface water impairment in California agricultural watersheds. In the San Joaquin Valley, approximately 50 and 100% of water samples collected from three different irrigation return flows exceeded the Escherichia coli standard of 126 cfu 100 mL⁻¹ and the enterococci standard of 33 cfu 100 mL⁻¹, respectively, as required for water discharge into state waterways. These results show that runoff from irrigated crops can contribute a significant load of bacteria indicators and potentially pathogenic microorganisms to waterways. Constructed wetlands are gaining recognition as a management practice for use in irrigated agriculture to reduce bacterial loads and a wide variety of water quality contaminants in agricultural return flows prior to discharge into waterways. Based on input-output sampling of four wetlands, 66-91% of E. coli concentrations and 86-94% of enterococci concentrations were retained in the wetlands. Removal efficiencies in terms of bacteria load were even higher, 80-87% and 88-97% for E. coli and enterococci, respectively, due to water losses (seepage and evapotranspiration) within the wetland. Of all the parameters considered, hydraulic residence time (HRT) appeared to be the factor having the greatest effect on the efficiency of bacteria indicator removal. Remarkably, a HRT of less than a day can achieve considerable bacteria indicator retention (∼70%), which allows for relatively small wetland areas being able to treat runoff from large agricultural areas (up to 360:1 in this study).     

Simulated crop production under saline high water table conditions

Summary Many irrigated lands in semi-arid regions of the world are underlain with saline high water tables. Water management is critical to maintain crop productivity under these conditions. A multi-seasonal, transient state model was used to simulate cotton and alfalfa production under various irrigation management regimes. The variables included in-season water application of 1.0 or 0.6 potential evapotranspiration (PET), and 18 or 33 cm pre-irrigation amounts for cotton. The water table was initially at a 1.5m depth and a 9 dS/m salinity. A impermeable lower boundary at 2.5 m depth was imposed. Irrigation water salinity was 0.4 dS/m. Climatic conditions typical to the San Joaquin Valley of California were used for PET and precipitation values. The simulations were for no-lateral flow and also lateral flow whereby the water table was raised to its initial level prior to each irrigation event. Uniform application of 1.0 PET provided for relative cotton lint yields and alfalfa yields of 95% or more for at least 4 years. In-season irrigation of cotton with 0.6 PET had higher yields when associated with a 33 cm rather than an 18 cm pre-irrigation. Lateral flow provided for higher cotton lint yields production than the no-lateral flow case for each pre-irrigation treatment. The beneficial effects of lateral flow diminished with time because of the additional salt which accumulated and became detrimental to crop production. Substantial alfalfa yield reductions occurred after the first year when irrigation was set at 0.6 PET regardless of other conditions. Evaporation losses from the soil during the cotton fallow season were higher when the soil water content entering the fallow season were higher.Research was supported by the University of California Salinity/ Drainage Task Force     

Adaptive implementation of information technology for real-time, basin-scale salinity management in the San Joaquin Basin, USA and Hunter River Basin, Australia

Pollutant trading schemes are market-based strategies that can provide cost-effective and flexible environmental compliance in large river basins. The aim of this paper is to contrast two innovative adaptive strategies for salinity management have been developed in the Hunter River Basin, New South Wales, Australia and in the San Joaquin River Basin, California, USA, respectively. In both instances web-based stakeholder information dissemination has been a key to achieving a high level of stakeholder involvement and the formulation of effective decision support tools for salinity management. A common element to implementation of salinity management strategies in both the Hunter River and San Joaquin River basins has been the concept of river assimilative capacity as a guide for controlling export salt loading and the establishment of a framework for trading of the right to discharge salt load to the Hunter River and San Joaquin River respectively. Both rivers provide basin drainage and the means of exporting salt load to the ocean. The paper compares the opportunities and constraints governing salinity management in the two basins as well as the use of monitoring, modeling and information technology to achieve environmental compliance and sustain irrigated agriculture in an equitable, socially and politically acceptable manner. The paper concludes by placing into broader context some of the issues raised by the comparison of the two approaches to basin salinity management.     

不同家庭经营类型农户樱桃销售方式选择及原因——基于烟台市樱桃销售现状

针对烟台牟平区、福山区70位大樱桃种植户，采用调查问卷、电话采访的形式，对不同年龄、受教育程度、樱桃种植面积和收入等进行了调查。运用二元logistic模型，对不同家庭经营类型农户的销售渠道选择进行了实证研究，得出以下结论:专业化经营的农户更愿意选择销售给商贩，而兼业化经营的农户更愿意选择批发市场销售；种植面积大的农户偏向于选择批发市场销售的形式，且教育程度越高，互联网销售的程度越高；种植面积小的农户更倾向于以销往商贩的方式销售大樱桃。      

Economic analysis of integrated on-farm drainage management

The goal of integrated on-farm drainage management (IFDM) is to eliminate the discharge of subsurface drainage water from farms into waterways or evaporation ponds. Components of a typical IFDM system include improved irrigation practices, irrigation of salt-tolerant plants with drainage water, and on-farm disposal of drainage water using a solar evaporator. Costs of an IFDM system include initial investments, operation and maintenance, and the opportunity costs of land used for the solar evaporator and for irrigation of nonmarketable, salt-tolerant plants. The farm-level cost of an IFDM system increases with the proportion of farmland used to irrigate salt-tolerant plants. A conceptual framework for evaluating the farm-level costs of IFDM is presented, along with empirical analysis from California’s San Joaquin Valley.     

Environmental decision support system development for seasonal wetland salt management in a river basin subjected to water quality regulation

Seasonally managed wetlands in the Grasslands Basin on the west-side of California’s San Joaquin Valley provide food and shelter for migratory wildfowl during winter months and sport for waterfowl hunters during the annual duck season. Surface water supply to these wetlands contain salt which, when drained to the San Joaquin River (SJR) during the annual drawdown period, can negatively impact water quality and cause concern to downstream agricultural riparian water diverters. Recent environmental regulation, limiting discharges salinity to the SJR and primarily targeting agricultural non-point sources, now also targets return flows from seasonally managed wetlands. Real-time water quality management has been advocated as a means of continuously matching salt loads discharged from agricultural, wetland and municipal operations to the assimilative capacity of the SJR. Past attempts to build environmental monitoring and decision support systems (EDSS’s) to implement this concept have enjoyed limited success for reasons that are discussed in this paper. These reasons are discussed in the context of more general challenges facing the successful implementation of a comprehensive environmental monitoring, modelling and decision support system for the SJR Basin.     

Infrared canopy temperature of early-ripening peach trees under postharvest deficit irrigation

Canopy temperature measurements with infrared thermometry have been extensively studied as a means of assessing plant water status for field and row crops but not for fruit trees such as peaches. Like in many regions of the world, the lack of water is beginning to impact production of tree fruit such as peaches in the San Joaquin Valley of California. This is an area where irrigation is the only source of water for agricultural crops in the summer growing season. A two-year field study was conducted to assess plant water stress using infrared canopy temperature measurements and to examine its feasibility for managing postharvest deficit irrigation of peach trees. Twelve infrared temperature sensors were installed in a mature peach orchard which received four irrigation treatments: furrow and subsurface drip irrigation with or without postharvest water stress. During the two-year period, measured midday canopy to air temperature differences in the water-stressed postharvest deficit irrigation treatments were in the 5-7 °C range, which were consistently higher than the 1.4-2 °C range found in the non-water-stressed control treatments. A reasonable correlation (R² = 0.67-0.70) was obtained between stem water potential and the canopy to air temperature difference, indicating the possibility of using the canopy temperature to trigger irrigation events. Crop water stress index (CWSI) was estimated and consistently higher CWSI values were found in the deficit irrigation than in the control treatments. Results of yield and fruit quality assessments were consistent with the literature when deficit irrigation was deployed.     

Crop coefficients for drip-irrigated processing tomato

Drip irrigation of processing tomato is increasing in the San Joaquin Valley of California (USA), a major tomato production area. Efficient management of these irrigation systems requires reasonable estimates of crop evapotranspiration (ET_c) between irrigations. A common approach for estimating ET_c is to multiply a reference crop evapotranspiration (ET_o) by a crop coefficient. However, a review of literature revealed mid-season crop coefficients for processing tomato to range from 1.05 to 1.25. Because of this variability, uncertainty exists in the crop coefficients appropriate for drip irrigation in the San Joaquin Valley. Thus, a study was initiated to determine the ET_c of processing tomato for drip irrigation in commercial fields and then calculate crop coefficients from the ET_c and ET_o data for the west side of the San Joaquin Valley. Crop ET_c was determined at five locations using the Bowen Ratio Energy Balance Method (BREB). Canopy coverage was also measured using a digital infrared camera. Average crop coefficients ranged from about 0.19 at 10% canopy coverage to 1.08 for canopy coverage exceeding about 90%. A second order regression equation reasonably described a relationship between crop coefficient and canopy coverage. Generic curves describing crop coefficient versus time of year were developed for various planting times.     

Drip Irrigation of Tomato and Cotton Under Shallow Saline Ground Water Conditions

Artificial subsurface drainage is not an option for addressing the saline, shallow ground water conditions along the west side of the San Joaquin Valley because of the lack of drainage water disposal facilities. Thus, the salinity/drainage problem of the valley must be addressed through improved irrigation practices. One option is to use drip irrigation in the salt affected soil.A study evaluated the response of processing tomato and cotton to drip irrigation under shallow, saline ground water at depths less than 1 m. A randomized block experiment with four irrigation treatments of different water applications was used for both crops. Measurements included crop yield and quality, soil salinity, soil water content, soil water potential, and canopy coverage. Results showed drip irrigation of processing tomato to be highly profitable under these conditions due to the yield obtained for the highest water application. Water applications for drip-irrigated tomato should be about equal to seasonal crop evapotranspiration because yield decreased as applied water decreased. No yield response of cotton to applied water occurred indicating that as applied water decreased, cotton uptake of the shallow ground water increased. While a water balance showed no field-wide leaching, salinity data clearly showed salt leaching around the drip lines.     

Irrigation in the Jordan Valley: Are water pricing policies overly optimistic?

Water is very scarce in the Hashemite Kingdom of Jordan. The development of both public irrigation in the Jordan Valley and private groundwater schemes in the highlands has diverted a large share of the country's water resources to agriculture. Many policy instruments have been used in the last 10 years to reallocate water to nonagricultural uses and encourage improvements in efficiency throughout the water sector. Demand management has been emphasized, with water pricing policies expected to instill conservation and motivate a shift toward higher-value crops. We examine the rationale for, and potential and current impact of, pricing policies in the Jordan Valley.We describe the likelihood of success of such policies in terms of operation and maintenance cost recovery, water savings and improved economic efficiency, and we explore some of the alternatives available for meeting these objectives. We show that while operation and maintenance (O&M) costs can be recovered higher water prices have limited potential for achieving gains in irrigation efficiency. The current system of quotas, the lack of storage, and technical difficulties experienced in the pressurized networks indicate that little water can be saved. More substantial increases in water prices can be expected to raise overall economic efficiency by motivating farmers to intensify cultivation, adopt higher-value crops, improve technology, or rent out their land to investors. Yet such strategies are constrained by lack of capital and credit, and pervasive risk, notably regarding marketing. Pricing policies, thus, are best implemented together with positive incentives that reduce capital and risk constraints, and offer attractive cropping alternatives or exit options with compensation.     

Calibration and validation of a three-dimensional subsurface irrigation hydrology model

An enhanced subsurface irrigation hydrology model, developed by Buyuktas & Wallender (Journal of Irrigation and Drainage Engineering, ASCE 128(3): 71–81), is calibrated and validated using 2 years of data collected in a field in Broadview Water District in California, USA. The first year data is used to calibrate the model, while the second year data is used for model validation. Calibration of the model is achieved by trial-and-error adjustments of model parameters to match simulated results with measured cumulative drain flow, water table depth and salinity of the drain flow. Adjustments of the model input parameters include van Genuchten soil hydraulic function parameters (n and K_s), maximum allowed pressure head at the soil surface and irrigation duration. For validation of the model, a particular case is chosen to match the measured drain flow, water table depth and drain flow salinity, based on the graphical and objective functions used. It is found, through model validation, that the predicted drain flow is slightly lower than the observed data, while the predicted water table depth is slightly higher.     

基于DP-PSO算法的灌区农业水资源优化配置

针对引水灌区,考虑灌溉用水总量约束和时段可供水量约束,以单一作物非充分灌溉下灌溉制度优化为第一层,区域多种作物种植结构及水量分配为第二层,分别采用动态规划和粒子群算法求解,建立了基于DP-PSO算法的灌区农业水资源优化配置模型。针对多重约束问题,提出了一种初始化粒子群的方法,并通过粒子速度的动态变化来保证每代粒子都满足约束,提高了算法的收敛速度和收敛精度。以赣抚平原灌区为对象,考虑降雨和水源可供水量不同步的特点,计算了3种降雨频率、多年可供水条件下的农业水资源优化配置方案。结果表明,基于DPPSO算法的农业水资源优化配置模型合理可靠,为引水灌区农业水资源优化提供了一种新的方法。     

Managing irrigation and drainage systems in arid areas in the presence of shallow groundwater: case studies

Two field studies were conducted on the west side of the San Joaquin Valley of California to demonstrate the potential for integrated management of irrigation and drainage systems. The first study used a modified cotton crop coefficient to calculate the irrigation schedule controlling the operation of a subsurface drip system irrigating cotton in an area with saline groundwater at a depth of 1.5 m. Use of the coefficient resulted in 40% of the crop water requirement coming from the groundwater without a loss in lint yield. The second study evaluated the impact of the installation of controls on a subsurface drainage system installed on a 65 hectare field. As a result of the drainage controls, 140 mm less water was applied to the tomato crop without a yield loss. A smaller relative weight of tomatoes classified as limited use, was found in the areas with the water table closest to the soil surface.     

Economic and agronomic strategies to achieve sustainable irrigation

The achievement of sustainable irrigation in arid regions requires greater attention to waterlogging, salinization, and degradation of ground and surface waters, which are among the problems that continue to threaten productivity and degrade environmental quality. We consider sustainability to be achieved when irrigation and drainage are conducted on-farm, and within irrigation districts, in a manner that does not degrade the quality of land, water, and other natural resources, either on-farm or throughout an irrigated region. Sustainability may also be described as maintaining the productive resources required for irrigation, so that future generations may have the same opportunity to use those resources as we do. Given the increasing importance of irrigated land for food production, the time has come when it is vital to intercept, reuse, and isolate drainage waters within the regions in which they are generated. Adoption of this strategy can be enhanced by policies that require farmers, and irrigation districts, to consider the off-farm impacts of irrigation and drainage. Such policies include linking water rights with salt rights to require the monitoring and management of both irrigation water and the salt loads in drainage waters. We review the knowledge gained since the early 1970s regarding the economic and agronomic aspects of irrigation and drainage, with a focus on drainage water reduction and sequential reuse of drainage water on salt-tolerant crops. Economic incentives that motivate farm-level and district-level improvements in water management are also reviewed. We conclude that adequate knowledge exists for implementing strategies that focus on water use and salt disposal within irrigated regions, and we recommend policies that will motivate improvements in productivity and enhance the likelihood of achieving sustainability.