Soil water in relation to irrigation, water uptake and potato yield in a humid climate

Efficiently controlling soil water content with irrigation is essential for water conservation and often improves potato yield. Volumetric soil water content (θ_v) in relation to irrigation, plant uptake, and yield in potato hills and replicated plots was studied to evaluate four water management options. Measurements of θ_v using a hammer driven probe were used to derive a θ_v index representing the relative θ_v status of replicated plots positioned along a hill slope. Time series for θ_v were determined using time domain reflectometry (TDR) probes at 5 and 15 cm depths at the center, shoulder, and furrow locations in potato hills. Sap flow was determined using flow collars in replicated field plots for four treatments: un-irrigated, sprinkler, surface drip, and sub-surface drip irrigation (40 cm depth). Irrigated yields were high/low as the θ_v index was low/high suggesting θ_v excess was a production problem in the wetter portions of the study area. The diurnal pattern of sap flow was reflected in the θ_v fluctuation it induces at hill locations with appreciable uptake. Hill locations with higher plant uptake were drier as was the case for the 5 cm (dry) depth relative to the 15 cm (wet) depth and for locations in the hill (dry) relative to the furrow (wet). The surface drip system had the lowest water use requirement because it delivers water directly to the hill locations where uptake is greatest. The sub-surface drip system wetted the hill gradually (1-2 days). Measurement of the θ_v index prior to experimental establishment could improve future experimental design for treatment comparisons.     

Temporal and spatial soil water management: a case study in the Heilonggang region,PR China

Long-term over-extraction of groundwater since the 1980s in the Heilonggang region, the East Hebei Plain of North China, has led to serious environmental problems such as seawater or saline water invasion into fresh water, land subsidence, etc. The conflicts between socio-economic development, water shortage and environmental degradation have become increasingly critical. Agriculture, the largest water user in the area and requiring 84% of total water supplied, is creating an unsustainable demand. Soil water is a very important resource in the Heilonggang region as 76% of mean annual precipitation becomes soil water. Effective use of this soil water is, thus, a key for full rational utilisation of water resources in the area. A concept of temporal and spatial management of soil water (TSMSW) is proposed here as a means to ensure effective use of soil water, viz.: management of soil water in full time and possible space dimensions and readjustment of crop distribution in order to harmonise as much as possible crop water demand and soil water availability. Four aspects are included: readjusting crop structures and rotations to fit changes in soil water, increasing the soil water resources, reducing soil water evaporation and managing soil water to meet temporal and spatial crop water demand. Field experiments show that temporal and spatial management of soil water can significantly increase water use efficiency (WUE). For cotton, adopting an integration of micro-topography and plastic mulch has increased WUE from 0.49 to 0.76–0.86 kg/m³; stalk mulch with manure for winter wheat reached to 2.41 kg/m³ and straw mulch with deep furrows (micro-topography) for summer maize increased it from 2.06 to 2.34 kg/m³.     

Effects of soil tillage and fallow management on soil water storage and sunflower production in a semi-arid Mediterranean climate

Normally sown in March in the region of Meknès (Morocco), rainfed sunflower suffers from a severe water deficit from anthesis which seriously affects grain filling. Increasing the stored soil water by appropriate management during the long period of bare soil preceding sunflower planting could be an opportunity which has not been explored for this spring-sown crop.Five methods for autumn soil tillage (mouldboard ploughing, chiselling, paraploughing, disc harrowing, no tillage) and four fallowing methods (chemical weed control, mechanical weeding, allowing weeds and volunteer crops, sowing barley) were compared in Meknès between 1994 and 1998 on calcimagnesic soils with vertic behaviour. Two additional experiments were carried out in 1997 and 1998 to create a range of leaf area indexes and transpiration requirements for sunflower. This was obtained (i) in 1997, by four levels of plant density (2.5–10.0 plants/m²) and three levels of soil water at planting (89, 37, and 29% of total available soil water); (ii) in 1998, by six levels of sunflower defoliation at star bud stage. Simulations with the EPIC-Phase model were performed to explore a wider range of weather conditions (1960–1998) than experienced.The differences in water storage at planting were explained partly by the mode of action of each of the implements tested and partly by the weather conditions which prevailed during the fallow period. After a very dry fallow period (with a frequency less than 1 year in 10), water storage was maximal after disc harrowing and paraploughing (including straw mulching) because soil layers were only marginally exposed to evaporation. Conversely, in a year with a wet fallow period (with a frequency of 4 years in 10), mouldboard and chisel ploughing gave the largest water reserves at planting because of better infiltration at depth with increased porosity. When the fallow period was initially wet, but dry in early spring (with a frequency of 2 years in 10), minimum and no tillage gave the best water storage but the differences between tillage methods were small. In spite of differences in soil water content at planting and clear differences in rooting systems, sunflower yield and seasonal water use were not significantly affected by soil tillage provided that the plant population was the same and weed control was adequate in reduced tillage systems. However, chisel ploughing was a good compromise for maximising stored water at sunflower planting on the clay soils of Meknès.Surprisingly, maximizing soil water content at sunflower planting was not systematically the best solution for maximizing sunflower yield and water use efficiency under the semi-arid conditions of Meknès. A high soil water content at planting leads to excessive leaf area index at the bud stage and consequently to rapid water depletion and yield reduction, especially when seasonal precipitation is low. A 50% refilling of the soil water reserve is sufficient for spring-sown sunflower as was confirmed by the simulation study. Soil moisture in the uppermost layer which governs seedling establishment is a more limiting factor for sunflower yield than total soil water content at planting.     

Effects of water table management on soil salinity and alfalfa yield in a semi-arid climate

A lysimeter experiment was conducted to investigate the effect of water table management (WTM) on distribution of soil salinity and annual alfalfa (Medicago scutellata) yield. Subirrigations with three levels of water table namely, 0.5 (WT0.5), 0.7 (WT0.7), and 1.0 m (WT1.0) and a free drainage (FD) conventional irrigation treatment were selected for this study. All treatments were arranged in a complete randomized block design with three replicates. The results of this study indicated that the average soil electrical conductivity of the saturated extract (ECe) in the root zone gradually increased and exceeded the designated crop threshold value (4 dS/m) after the first forage harvest in subirrigated lysimeters. A higher salt accumulation was observed at the WT0.5 treatment. The average dry matter yield of annual alfalfa in WT0.5 and WT0.7 treatments was found to be 52 and 73% higher compared with the control treatment, respectively.     

Modelling the effects of climate variability and water management on crop water productivity and water balance in the North China Plain

In the North China Plain (NCP), while irrigation using groundwater has maintained a high-level crop productivity of the wheat-maize double cropping systems, it has resulted in rapid depletion of groundwater table. For more efficient and sustainable utilization of the limited water resources, improved understanding of how crop productivity and water balance components respond to climate variations and irrigation is essential. This paper investigates such responses using a modelling approach. The farming systems model APSIM (Agricultural Production Systems Simulator) was first calibrated and validated using 3 years of experimental data. The validated model was then applied to simulate crop yield and field water balance of the wheat-maize rotation in the NCP. Simulated dryland crop yield ranged from 0 to 4.5 t ha⁻¹ for wheat and 0 to 5.0 t ha⁻¹ for maize. Increasing irrigation amount led to increased crop yield, but irrigation required to obtain maximum water productivity (WP) was much less than that required to obtain maximum crop yield. To meet crop water demand, a wide range of irrigation water supply would be needed due to the inter-annual climate variations. The range was simulated to be 140-420 mm for wheat, and 0-170 mm for maize. Such levels of irrigation applications could potentially lead to about 1.5 m year⁻¹ decline in groundwater table when other sources of groundwater recharge were not considered. To achieve maximum WP, one, two and three irrigations (i.e., 70, 150 and 200 mm season⁻¹) were recommended for wheat in wet, medium and dry seasons, respectively. For maize, one irrigation and two irrigations (i.e., 60 and 110 mm season⁻¹) were recommended in medium and dry seasons, while no irrigation was needed in wet season.     

SPFC: a tool to improve water management and hay production in the Crau region

This article deals with the development and application of SPFC, a model used to improve water and grassland production (HC) in this region of France. This model is composed of two sub-models: an irrigation model and a crop model. As the fields are border-irrigated, these two sub-models are coupled. The crop model simulates dry matter (DM), leaf area index (LAI) and soil water reserve (SWR) variations. LAI and SWR are both used for border model updating: SWR for the deficit of saturation required by the infiltration equation and LAI for the roughness coefficient n. After calibration and validation, SPFC is then used to identify realistic management strategies for the irrigation and production system at the plot level. By scheduling irrigation when SWR is 50% depleted, would result in a low Dry Matter DM production loss (around 10%), reduced labour (eight irrigation events instead of 11) and in significant water saving compared with farmers’ practices, on the basis of an average climatic scenario. Furthermore, this improvement of irrigation efficiency is not incompatible with groundwater recharge used for the potable water supply of the region.     

Water balance and crop coefficients of summer-grown peanut (Arachis hypogaea L.) in a humid tropical region of India

A field experiment was conducted with a bunched variety of peanut (Arachis hypogaea L.) cv. JL-24 during the summer seasons (March–June) of 1992 and 1993 in the humid tropical canal command area at the University Experimental Farm, Memari (23°1 N, 88°5 E and 21.34 m a.s.l) in West Bengal of eastern India. The soil at the site is of sandy loam (Typic Fluvaquent) texture and the area has a shallow water table. Weekly and seasonal field water balance components of actual evapotranspiration (ETa) including the capillary contribution into root zone were determined. Peanut yield and water productivity were determined for three ratios of irrigation water and cumulative pan evaporation (CPE) of 0.9, 0.7 and 0.5. Mean crop coefficients were determined for each 7-day period of growth and were related to leaf area index and growing degree-days. Average seasonal values of ETa of peanut were 434, 391 and 356 mm for the three treatments, respectively, for 115 days of growth. The total pod yield and WP were significantly higher in 0.9 IW:CPE treatment in the 1992 season. On an average, 0.9 IW:CPE treatment had 7 and 11% higher yields in 1992 and 1993, respectively, over treatments 0.7 and 0.5 IW:CPE. The maximum average Kc of 1.19 occurred about 9 weeks after sowing relative to grass reference ET (ETo).     

Estimating the demand for irrigation water in a humid climate: A case study from the southeastern United States

The southeastern United States typically receives more than 130 cm of precipitation per year. In this region, as in others around the world, irrigation is used as a supplement to rainfall. Over the past thirty years the number of hectares under irrigation in the region has grown considerably, as has population. Policy makers are currently searching for effective tools to address water demand. This study tests the effect of water costs, crop prices and technology on the multiple crop production decision using supplemental irrigation. Results for Georgia row crop producers indicate water demand is modestly affected by water price (with elasticities between −0.01 and −0.17), but more so by crop price (with elasticities between 0.5 and 0.82). Results also suggest adoption of lower pressure irrigation systems does not necessarily lead to lower water application rates on corn, cotton, peanuts, and soybeans.     

Evapotranspiration predictions: a comparison among GLEAMS,Opus, PRZM-2, and RZWQM models in a humid and thermic climate

Environmental fate models are increasingly used to evaluate potential impacts of agrochemicals on water quality to aid in decision making. However, errors in predicting processes like evapotranspiration (ET), which is rarely measured during model validation studies, can significantly affect predictions of chemical fate and transport. This study compared approaches and predictions for ET by GLEAMS, Opus, PRZM-2, and RZWQM and determined effects of the predicted ET on simulations of other hydrology components. The ET was investigated for 2 years of various fallow–corn growing seasons under sprinkler irrigation. The comparison included annual cumulative daily potential ET (ET_p), actual ET, and partitioning of total ET between soil evaporation (E_s) and crop transpiration (E_t). When measured pan evaporation was used for calculating ET_p (the pan evaporation method), Opus, PRZM-2, and RZWQM predicted 74, 65, and 59%, respectively, of the 10-year average ET reported for a nearby site. When the energy-balance equations were used for calculating ET_p (the combination methods), GLEAMS, Opus, PRZM-2, and RZWQM predicted 84, 105, 60, and 72% of the reported ET, respectively. The pan evaporation method predicted a similar amount of ET to the combination methods for bare soil, but predicted less ET when both E_s and E_t occurred. RZWQM reasonably predicted partitioning of ET to E_s, while GLEAMS and Opus over-predicted this partitioning. A close correlation between soil water storage in the root zone and ET suggests that accurate soil water content predictions were fundamental to ET predictions. ©     

Agricultural water management in water-starved countries: challenges and opportunities

Agriculture commands more water than any other activity on this planet. Although the total amount of water made available by the hydrologic cycle is enough to provide the world’s current population with adequate freshwater, most of this water is concentrated in specific regions, leaving other areas water-deficient. Because of the uneven distribution of water resources and population densities worldwide, water demands already exceed supplies in nearly 80 countries with more than 40% population of the world. Consequent to future population increase in these countries, supplies of good-quality irrigation water will further decrease due to increased municipal–industrial–agricultural competition. These facts reveal that the time has come for the sustainable management of available water resources based on global, regional, and site-specific strategic options: (1) understanding the concept of ‘virtual water’ and potential use of this water as a global solution to regional deficits, i.e. the water-short countries may import a portion of food crops or other commodities that require more water and export those that need less water in production; (2) improvement in current efficiencies of agricultural water use and conservation, both in the rain-fed and irrigated agriculture, i.e. to produce more with the existing resources with minimum deterioration of land and water resources; (3) use of efficient, economic, and environmentally acceptable methods for the amelioration of polluted waters and degraded soils, and (4) re-use of saline and/or sodic drainage waters via cyclic, blended, or sequential strategies for crop production systems, wherever possible and practical. We believe that these strategies will serve as the four pillars of integrated agricultural water management and their suitable combinations will be the key to future agricultural and economic growth and social wealth, particularly in regions that are deficient in freshwater supplies and are expected to become more deficient in future.     

Agricultural water management and poverty linkages

Water is critically important to the livelihoods of more than 1 billion people living on less than $1 a day, particularly for the 850 million rural poor primarily engaged in agriculture. In many developing countries, water is a major factor constraining agricultural output, and income of the world's rural poor. Improved agricultural water management can contribute to poverty reduction through several pathways. First, access to reliable water improves production and productivity, enhances employment opportunities and stabilizes income and consumption. Secondly, it encourages the utilization of other yield-enhancing inputs and allows diversification into high-value products, enhances nonfarm outputs and employment, and fulfils multiple needs of households. Third, it may contribute either negatively or positively to nutritional status, health, societal equity and environment. The net impact of agricultural water management interventions on poverty may depend individually and/or synergistically on the working of these pathways. Improved access to water is essential, but not sufficient for sustained poverty reduction. Investments are needed in agricultural science and technology, policies and institutions, economic reform, addressing global agricultural trade inequities, etc. But how best to match the agricultural water management technologies, institutions and policies to the needs of the heterogeneous poor living in diverse agro-ecological settings remains unclear. This article provides a menu of promising pathways through which agricultural water management can contribute to sustained poverty reduction.     

Relations between available and extractable soil water and evapotranspiration from a bean crop

The accuracy of ‘available’ and ‘extractable’ soil water estimates was investigated using irrigated and unirrigated beans (Vicia faba) grown in an alluvial silt loam in Canterbury, New Zealand. Available water capacity was defined as the difference between soil water contents in the root zone at the drained upper limit (DUL) and at the lower limit (LL) as estimated by laboratory procedures. Extractable water capacity was specified as the difference between field estimates of DUL and LL for the whole profile affected by roots. DUL was estimated in the laboratory by equilibrating soil cores at matric potentials at ?10, ?20 or ?30 kPa, and in the field by neutron moderation. Laboratory estimates of LL were made from soil samples equilibrated at ?1.5 MPa matric potential. In the field LL was measured by neutron moderation on plots where evaporation had apparently ceased due to drought stress.When compared at intervals down the profile laboratory estimates of DUL and LL showed poor agreement with field observations. However, the final estimates of available and extractable water capacities were similar because of compensatory inaccuracies in the laboratory estimates. Furthermore, field measurements of evapotranspiration, using neutron moderation and tensiometry, indicated that the accuracy of the available water estimates was much reduced by upward fluxes of water into the rooting zone. These fluxes resulted in water extraction to at least 1.0 m although the apparent maximum rooting depth (measured by counting roots washed from soil cores) was only 0.7 m.Particular attention was paid to the influence of subsoil textural variability, which is pronounced in such soils. Laboratory and field estimates of the LL had to be carefully matched texturally before relevant comparisons could be made. Problems associated with subsoil textural variability affected laboratory methods of DUL estimation more than field methods.     

Responses of crop yield and water use efficiency to climate change in the North China Plain

Based on future climate change projections offered by IPCC, the responses of yields and water use efficiencies of wheat and maize to climate change scenarios are explored over the North China Plain. The climate change projections of 21st century under A2A, B2A and A1B are from HadCM3 global climate model.A climate generator (CLIGEN) is applied to generate daily weather data of selected stations and then the data is used to drive CERES-Wheat and Maize models. The impacts of increased temperature and CO₂ on wheat and maize yields are inconsistent. Under the same scenario, wheat yield ascended due to climatic warming, but the maize yield descended. As a more probable scenario, climate change under B2A is moderate relative to A2A and A1B. Under B2A in 2090s, average wheat yield and maize yield will respectively increase 9.8% and 3.2% without CO₂ fertilization in this region. High temperature not only affects crop yields, but also has positive effect on water use efficiencies, mainly ascribing to the evapotranspiration intensification. There is a positive effect of CO₂ enrichment on yield and water use efficiency. If atmospheric CO₂ concentration reaches nearly 600 ppm, wheat and maize yields will increase 38% and 12% and water use efficiencies will improve 40% and 25% respectively, in comparison to those without CO₂ fertilization. However, the uncertainty of crop yield is considerable under future climate change scenarios and whether the CO₂ fertilization may be realized is still needed further research.     

Stability of crop coefficients under different climate and irrigation management practices

Summary The effects to climate and management practices on crop water requirement coefficients were studied for a soybean crop growing on a sandy soil using a mechanistic model that computes evaporation and transpiration in response to soil, crop, and climatic factors. It was found that seasonal errors could the as high as 190 mm when crop coefficients developed under one set of conditions were used under different climate and management conditions. The largest error in ET occurred when vapor pressure was reduced from 26 mb to 14 mb; next in importance were site differences in wind speed, radiation, irrigation interval, temperature and planting date. Correction factors needed to adjust crop coefficients to those site specific conditions ranged from 0.73 to 1.30 depending on the time of season and climate or management variable that was changed. When the overall crop coefficient was divided into a plant specific and a soil specific coefficients, the plant coefficient was relatively stable compared to soil coefficients. The results of this study can help establish a practical range of conditions over which crop coefficients developed at one site can be used to compute the appropriate values for sites where measurements have not been made.Approved for publication as Florida Agricultural Experiment Station Journal Series No. 9514. This research was partially supported by the US AID project, International Benchmark Sites Network for Agrotechnology Transfer, No. DAN-4054-c-00-2071-00     

Evaluation of the water cost effect on water resource management:: Application to typical crops in a semiarid region

The greatest water consumption takes place during irrigation of arid and semiarid areas, therefore, water resource management is fundamental for sustainability. For correct management, several tools and decision-making systems are necessary while paying close attention to aspects such as profitability, water cost, etc. Water resources are scarce and some of them are of low quality. This extremely delicate situation occurs in some regions of the world and it explains increasing water cost. In Europe, the policies relating to water use (2000/60/EC) pay particular attention to the need of its protection and conservation. To ensure this, a large number of measures, including the establishment of prices which really correspond to their usage costs, have been set forth. Water subsidies are relatively important in all European countries. In this study, a specific methodology is applied to a Spanish semi-arid region. It is useful and easy to apply, not only by farmers, but also by water managers and politicians in charge of policy. The methodology also helps in the decision-making process about water cost in agriculture. In this area (Hydrogeological System 08.29, Spain), the resources are mainly underground water with a high variable cost and without any direct subsidies. This model allows us to analyse the effect of different water costs and to find the optimum strategy giving the maximum gross margin in line with water cost and its main determining factors (irrigation system, climatic variability, etc.).The methodology is based on the effect of irrigation on crop yield with its production function, integrating the effect of application efficiency. In this way, a relationship between gross margin and gross irrigation depth is obtained. Working with permanent irrigation systems and four crops (barley, garlic, maize and onion), the main conclusion is that the optimum gross irrigation depths are always fewer than those necessary for maximum crop yield and when irrigation depths are fewer water cost increases. Irrigation depths, which maximise the economic efficiency in the use of water (€ m⁻³), are fewer than those which maximise the gross margin; therefore, this aspect must be considered in irrigation scheduling. The results also show important differences among crops, depending on their water requirements and their economic profitability.     

Response of tomatoes,a crop of indeterminate growth,to soil salinity

Tomatoes were grown in tanks filled with loam and clay, and were irrigated with waters of three different levels of salinity. Osmotic adjustment was determined by analysing the pressure–volume curves at four growth stages. Owing to the osmotic adjustment, tomatoes are able to maintain the turgor potential and the stomatal conductance at the same value for the lower values of the leaf-water potential. Salinity affected the pre-dawn leaf-water potential, stomatal conductance, evapotranspiration, leaf area and fruit yield on both soils. Soil texture only affected the fruit yield. The evapotranspiration showed a moderate decrease, owing to the small decrease in leaf area and the effect of osmotic adjustment on the stomatal conductance, whereas the fruit yield decreased strongly. The tomato plant apparently favours under saline conditions, the growth of foliage at the expense of fruit formation.     

Water requirements of young coconut palms in a humid tropical climate

Summary The evapotranspiration rates of five-year-old coconut palms (Cocos nucifera Linn. cv West Coast Tall) grown in an Oxisol on the West coast of India were quantified from soil moisture depletion studies and lysimetric measurements. The rates increased from 2.9 mm day^–1 in December to 5.5 mm day^–1 in April and reduced to 2.3 mm day^–1 in June following the onset of monsoon rain. Ratios of evatranspiration to class A pan evaporation were 0.87–0.88 in the moderate rainfall period (September and October), 0.78–0.85 in the winter period (November–February), 0.87–0.96 in the summer period (March–May) and 0.60–0.68 in the rainy period (June–August).     

An integrated model-approach to the effect of water management on crop yield

Quantifying the effect of drainage on crop yield is of essential importance in agricultural management. In this article a model is described with which this effect can be computed. For both arable land and grassland the factors acting in spring, summer and autumn are dealt with separately.Arable land. In spring sowing date is the main factor affecting the crop yield. Sowing date depends on the tillage conditions of the soil toplayer. By means of an existing model, the course in time of the soil water tension of the upper layer is simulated in connection with rainfall, evaporation, drain depth and drain intensity data. Using specific criteria on minimum soil water tension for tillage operations, the dates and number of workable days can be established from the model output. The expected yield depression is then derived, using an experimental relationship between yield depression and number of days of sowing delay.During the growing season the yield directly depends on the magnitude of the actual evapotranspiration. This value can be computed by means of a known evapotranspiration model for various drought frequencies, groundwater table depths in spring, drain intensities and amounts of water supplied. The yield can be obtained from the relationship between yield and relative evapotranspiration. Combining this yield with the yield depression obtained by means of the workability model gives the actual yield.In autumn crop yield is influenced by the working conditions during harvest. Via the workability model, the dates and the number of days available for harvesting are determined. Yields are derived from an experimental relationship between yield depression and number of days of earlier harvesting. An example is given for summer cereals growing on a heavy sandy loam soil under meteorological conditions prevailing in The Netherlands.Grassland. The effect of shallow groundwater table depths in winter and spring on the yield of the first and second cut can be determined with the workability model in an identical manner to that given for arable land. Because of lack of data, a slightly different approach was followed in this paper. With the workability model the course of groundwater table depth during winter and spring can be simulated and the mean depth determined. From the relation between yield depression and mean groundwater table depth over the period November through May the yield depression can be found. Combining this with the yield obtained with the evapotranspiration model gives the actual yield. An example representative for The Netherlands is given for grass on peat soil.     

作物水氮耦合对农田土壤环境的影响

作物所处的土壤环境对提高作物产量和品质至关重要。为深入研究土壤生产力可持续发展提供理论依据,迫切需要了解现阶段作物水氮耦合效应对土壤环境的影响,重点总结了作物水氮耦合效应对土壤容重、孔隙度、含水量、温度、养分、有机质、酶活性、微生物和气体排放等土壤环境的影响,并提出未来水氮耦合的重点研究方向,以期为土壤的高效生产和可持续利用提供理论依据。      

RZWQM: Simulating the effects of management on water quality and crop production

The interactive use of experimentation and modeling is an efficient way to devise and test new agricultural management systems. The Root Zone Water Quality Model (RZWQM) is a comprehensive simulation model designed to predict the hydrologic response, including potential for groundwater contamination, of alternative crop-management systems. The model is one-dimensional (vertical into the soil profile) and integrates physical, biological and chemical processes. It simulates crop development and the movement of water, nutrients and pesticides over and through the root zone for a representative unit area of an agricultural field over multiple years. RZWQM allows for a variety of management practices: tillage; irrigation, fertilizer, manure and pesticide applications; tile drainage and crop rotations. Several significant validation efforts have shown the usefulness of RZWQM for evaluating and developing management scenarios.