Field Water Balance Research Articles

Effects of four cultivation systems for maize on nitrogen leaching 2. Model simulation

The GLEAMS simulation model (version 2.03) was used to analyse the experimental results presented in M. Borin et al., 1996 (M. Borin C. Giupponi and F. Morari, 1996. Effects of four cultivation systems for maize crop on nitrogen leaching in shallow water. 1. Field experiment. Eur. J. Agron., 5: 295–306) and to derive useful indications on the environmental impacts of the four maize cultivation systems. On the basis of a first test it was found necessary to introduce in the model a subroutine to represent the phenomenon of crack flow (water movement through soil cracks). The modified model (GLEAMS-CF), tested on the experimental data, demonstrated better capability of simulating the field water balance and the nitrogen leaching and was therefore used to simulate the most probable long-term nitrogen leaching that would occur in the various cultivation systems. This was done using a 100-year record created using a climate simulator. This exercise revealed a wide variation in nitrogen leaching caused by the four different cultivation systems studied. Average simulated nitrogen leaching in the four systems were: 85 (system A), 42 (system B), 20.4 (system C) and 19.8 kg ha −1 year −1 (system D).

The Monitoring Forecasting Assessing Decision-Making Service System of Soil Moisture Stress of Winter Wheat and Its Application in North China Region

During the growing season of winter wheat, the precipitation amount in the North China Region, where the water resource is seriously insufficient, amounts to only 100-250mm and can not meet the demand of winter wheat.This paper demonstrated the geographic distribution of the difference between the water demand and supply of winter wheat in different climatic years (guaranteed probability of precipitation during growth period of winter wheat at 75%, 50% and 25% respectively). The water differences were calculated with a field water balance equation.To determine proper irrigation time and amount, and to ensure stable and high production of winter wheat with limited water resource, Monitoring Forecasting Assessing Decision-Making Service System (MFADSS) of soil moisture stress of winter wheat was constructed on the basis of experimental research on the relationship between soil moisture and winter wheat. The techniques and functions of each subsystem are also demonstrated.The system was applied to more than 3 million ha. of winter wheat in 90 counties of the North China Region. Accuracy of the decision of the irrigation reached about 95 per cent. The water-saving and high yield function of the system was shown clearly. Obvious social, economical and ecological benefits were obtained during 1990-1995 under the support of the government.

WATER BALANCE OF FIELD PLOTS PLANTED WITH SOYBEAN AND PUMPKIN

A field water balance was studied within the context of the Japanese plan for upland field agriculture. As part of this study, soil physical conditions were monitored in the field, soil hydraulic characteristics were measured in the laboratory, and the water balance was modeled. The soil hydraulic characteristics were described by the analytical functions of van Genuchten and Mualem, and were used as inputs in the SWAP 1993 water balance model. The model calculation of actual evapotranspiration, ETa, agreed well in some instances with the field ETa calculated using the Energy balance - Bowen ratio method but did not agree at other times. Good results were obtained for the two situations considered as calculated soil water contents agreed fairly well with indirectly measured values (i.e., from tensiometer data) in the field. However, a sensitivity analysis will be necessary if quantitative conclusions are to be made.

TESTING OF A WATER LOSS DISTRIBUTION MODEL FOR MOVING SPRINKLER SYSTEMS

Field water balance measurements using monolithic lysimeters were used in validating the Cupid-DPE model for predicting water loss partitioning during sprinkler irrigation from a moving lateral system fitted with impact sprinklers and spray nozzles. The model combines equations governing water droplet evaporation and droplet ballistics with a comprehensive plant-environment energy balance model. Comparisons indicate good agreement between measured and modeled transpiration, and the measured and modeled soil evaporation during the day of irrigation. Total predicted evapotranspiration during the day of irrigation was greater than measured totals using the monolithic lysimeters. However, part of this difference was because the lysimeters could not measure water use during irrigation. Total measured and predicted evapotranspiration agreed well for the day following irrigation. Predicted soil evaporation rates matched well for the period immediately following irrigation, and cumulative soil evaporation was nearly identical to the measured total through the end of the next day. During irrigation, the main water loss was shifted from transpiration to evaporation of the wetted-canopy. For equal application volumes, the duration of this effect was greater using impact sprinklers due to the greater wetted diameter and lower average application rate compared to spray nozzles. Predicted water flux rates during irrigation were up to 50% greater for canopy evaporation than for transpiration rates predicted immediately prior to the start of irrigation. Canopy evaporation amounted to 69% and 63% of the total predicted water use during impact and spray irrigation, respectively. It also was 0.69 and 0.28 mm greater, respectively, than the predicted transpiration total during this same time span assuming no irrigation had been applied. About 13 and 5% of the water applied by overhead sprinkling was evaporated or transpired during impact and spray irrigation, respectively. However, the net increase in predicted water loss during irrigation was only 5.8% and 2.4% of the irrigated water depth applied for the impact and spray cases, respectively, because transpiration and soil evaporation would have occurred even without irrigation. Although droplet evaporation represented less than 1% of the total water loss for the day using either type of sprinkler, irrigation water did influence the energy transfer between the plant-environment and water droplets during flight, on the canopy, and the soil.

Determination of Evapotranspiration from A Maize Field under Drought Conditions

During the growing seasons of the last 5 years, we have experienced 3 summer droughts and 1 cool rainy summer. Accurate field water balance information is necessary to manage soil water for stable productivity under such varying conditions.It is well known that shortages of soil moisture in the root zone result in decreases in evapotranspiration (ET). Such conditions stimulate the root systems of many crops to develop into the deeper soil layer to prevent injury from drought. In this paper, the authors present a method to determine ET from fields of maize in consideration of root spread (depth & width) and soil moisture condition in the total root zone.Suzuki & Nakayama (1996) observed high ET rates from a maize field under drought conditions, despite soil moisture conditions in the surface to 1.0m soil layer being less than that required for optimum growth. They showed that ET under such conditions proceeded by water uptake from soil deeper than 1.0m. Those findings suggested that the evaluation of ET from soil moisture content data for only the shallow upper layer may underestimate the actual ET, and this underestimation leads to inadequate control of soil moisture for optimum crop production. Here the authors present a new formula for estimating the actual ET, taking the root system and soil moisture content in the soil mass of the total root zone into account. The accuracy of this formula depends on knowledge of the soil layer of the deepest root end in each growth stage. However, measuring this soil depth is troublesome, a new formula presented in this paper would be more practical if this depth could be estimated based on plant growth stage.

Modeling water balance components in relation to field layout in lowland paddy fields. I. Model development

In this study, a water balance model applicable to lowland paddy fields was developed. The model inputs consist of irrigation supply, climatic data, soil parameters and layout dimensions. The model is formulated to simulate various processes such as evapotranspiration, seepage and percolation, and surface runoff as they occur in the field water balance system. The model is able to predict the changes in water balance components under different land management and hydrological conditions. The model can be applied either for plot-to-plot or independent plot layouts. It was validated using data collected from controlled plot experiments. The details of model development and validation are outlined in this paper.

Sensitivity of Simulated Field Water Balance to Different Soil Hydraulic Data

Knowledge of a model’s response to soil hydraulic data generated by different methods can be used in selecting appropriate model soil hydraulic parameters. Four different sets of soil hydraulic data, comprising the air entry potential, exponential parameter for the Campbell’s soil moisture release curve model (b-value), and saturated hydraulic conductivity values, were measured directly and predicted using soil particle size fractions and one known pair of soil moisture content and matric potential values. The parameters were used in executing the model LEACHW to approximate cornfield water balance under irrigated conditions. The predicted cumulative corn evapotranspiration and soil profile water storage values were compared with measured data to assess LEACHW’s response to different sets of soil hydraulic data and to select appropriate soil hydraulic data for LEACHW simulations.

Estimation of local and regional components of drain-flow from an irrigated field

The contribution of regional ground water and deep percolation from a furrow irrigated field to total drain flow was estimated using salt load analysis. It was found that 64% of the drain flow comes from regional ground water flow. The electrical conductivity of the drain water was highly correlated with the drain flow rate. From the field water balance with deep percolation as estimated from the salt load analysis, using yield function derived evapotranspiration, and measured changes in root zone water storage, it was shown that 14% of the crop evapotranspiration comes from ground water during the study period.

Macroscopic soil physical processes considered within an agronomical and a soil biological context

Soil physical conditions play an important role in determining the environment in which biological processes take place. These conditions can be defined at different spatial and temporal scales. For the main field site of the Dutch Programme on Soil Ecology of Arable Farming Systems it is demonstrated that a macroscopic soil physical approach gives useful information, also for processes on the micro-scale. The field site is described in a historical context, and new plots with different arable farming systems are studied. The field water balance is studied by monitoring soil physical conditions in the field, characterizing the hydraulic properties, modeling the water balance of the unsaturated zone, and calculating time-depth curves of parcels of water.The soil physical conditions of the plots with a different arable farming system were similar, except for an integrated system with minimum tillage. No relevant hydrological differences between the soil physical characteristics of the plots could be demonstrated. In all plots the groundwater level often came close to the soil surface, even in the growing season. These wet conditions are favorable for denitrification. The distance from a drain is an important factor determining the soil physical conditions in the topsoil under wet conditions, due to the curved phreatic surface.The water balance simulation results were not in good agreement with measured pressure heads. However, by using time-depth curves a good impression of the flow of water and the convective transport of solutes and could be obtained.

Evaluating three cotton simulation models under different irrigation regimes

Crop growth/irrigation scheduling simulation models are becoming an integral part of crop management schemes designed to maximize input use. The selection of a particular model over others must be based on the model's performance under local conditions. Three crop simulation models, COTTAM, GOSSYM and IRRSCH, were evaluated for their accuracy in approximating field-observed crop water stress index (CWSI) of cotton grown under different irrigation regimes in a semiarid environment. The purpose is to use CWSI measured in the field to evaluate and to select an appropriate simulation model to schedule irrigation for cotton production. Generally, CWSI predicted by the models was lower than the measured values. Comparatively, IRRSCH was the best of all the models in predicting CWSI regardless of the irrigation treatments. Statistical analysis showed no significant difference (at 95% significance level) between the measured and the predicted CWSI by IRRSCH when cotton was irrigated at −0.40 MPa in 1983. Analysis of variance of paired data showed that COTTAM and IRRSCH predicted similar CWSI ( P = 0.05) in cotton irrigated at −1.50 MPa in 1983. This study showed IRRSCH, a simple water balance model, is superior to COTTAM and GOSSYM in approximating CWSI at water stress levels most encountered in irrigated fields (−0.15 and −0.40 MPa) and best approximates field water balance.

Seasonal water balance of a sandy soil in Niger cropped with pearl millet, based on profile moisture measurements

In the Sahel, calculation of the field water balance from neutron-probe measurements is often difficult for pearl millet ( Pennisetum glaucum (L.) R. Br.), which is due to the rapid drainage ( D) of the sandy soils, on which it is typically grown. We present a simple method of calculating D in these soils from weekly neutron-probe data. The method divides the water balance into two phases. In the first, applicable early in the season, water flux across the maximum depth of probe measurement ( Z m) is assumed negligible, and evapotranspiration ( E) and D are calculated from the change in soil water content (θ) between the bottom of the rootzone ( Z r) and Z m, thus allowing calculation of unsaturated hydraulic conductivity, K( θ), from the flux across Z r. In the second phase, when soil water starts to percolate across Z m, D is calculated from K( θ), assuming a hydraulic head gradient of −1. The method is used to calculate a one-dimensional water balance of a pearl-millet crop grown in a deep sandy soil at two fertility levels during a season of normal rainfall. Results show that the calculated K( θ) functions compare well with those based on laboratory measurements. An acceptable estimate of drainage, and therefore E could be made. Mean cumulative E and D were, respectively, 211 and 207 mm for the unfertilized crop, and 268 and 148 mm for the fertilized crop with 440 mm of rainfall received during the crop cycle. The fertilized millet crop water balance was simulated, which compared to the calculation method resulted in an about 10% higher seasonal E and a 10% lower seasonal D. Our study shows that E can be corrected for D using a simple but accurate method, and consistent with other studies in the region indicates that rainfall is usually not the primary limiting factor to pearl-millet production.

Pesticide transport modelling in soil for risk assessment of groundwater contamination

The risk of groundwater contamination with pesticides applied to soil surface depends on the soil properties, the agricultural practices, the climatic influences, and on the properties of the pesticides themselves. The EXSOL model was developed for the simulation of the transport and fate of pesticides and organics in soils. The dynamics of mobility, accumulation and degradation can be studied under various soil and climatic conditions. Transient water flow is provided from a simulation model of the field water balance. The percentages of the herbicide 2,4,5‐trichlorophenoxyacetic acid in a luvisol soil after a single application in summer are compared with model calculations using sorption coefficients from laboratory column studies. The calculated percentages lie within the measured range, except for those in the deeper soil layer. The underestimation can be explained with preferential flow in macropores which may have occurred during the heavy rainfall six days after application.

A model to predict changes in soil moisture, NO3-N content and N uptake by wheat

A simulation model to predict fertilizer N behaviour in a soil-plant (wheat) system has been developed and tested. The model predicts components of field water balance (evaporation, transpiration, drainage and run-off) and changes in soil nitrogen amounts due to N transformations (urea hydrolysis, mineralization, nitrification and volatilization), N movement and plant N uptake using information on N transformation coefficients for the soil, atmospheric evaporative demand (Epan), leaf area development and root growth characteristics of the crop. The model predicts N uptake by wheat through mass flow using a new simplified crop cover function. The coefficients of correlation between the measured and predicted N uptake by wheat grown under three different moisture regimes in the two years (1987–88 and 1988–89) approached unity. The computed amount of residual NO3-N in the soil profile at wheat harvest matched well with the measured amount with a root mean square error of 13.7 percent. The close matching of the measured and model predicted components of nitrogen and water balances under three widely different set of irrigation treatments suggests of model's capabilities to help in on-farm N management both under irrigated and rainfed conditions.

Water Balance Estimation Model: Field Test and Sensitivity Analysis

AbstractA simplified, capacity‐based simulation model has been developed to predict components of the field water balance. This requires only daily information such as the atmosphere evaporative demand and soil‐wetting events, maximum available soil water storage, and root growth characteristics, as well as crop and soil parameters. Actual evapotranspiration was modeled using Eagleman's parameterization. The model was tested for upland rice grown on a 3500‐m2 field plot, and on an undisturbed lysimeter. The predicted actual evapotranspiration (AET) and drainage (D) at the bottom of the soil profile matched the lysimeter data. Also, the model predicted reasonably well the field soil water content data, which were obtained at 15 sites. In the latter case, the root mean square error was about 16% for the seasonal AET, and 19% for D. Errors were within the limits of experimental uncertainties expected when such measurements are analyzed by Darcy's law. The results of a sensitivity analysis with respect to changes in parameter inputs show that the model is physically realistic. However, the sensitivity depends strongly on the supply of water in the soil. This clearly justifies the need to simulate the root‐zone water balance as a time‐dependent process, especially if there is a practical interest in accurate prediction during drought periods.

Root Zone Water Balances of Three Low‐Input Millet Fields in Niger, West Africa

AbstractIt is often assumed that pearl millet [Pennisetum americanum (L.) Schum.] production is limited by water supply despite the fact that little published data exist on water balances of low‐input millet fields. The objectives of this study were to: (i) quantify components of the field water balance of three sites, each in a different rainfall zone, and (ii) determine whether water supply was the primary limiting constraint to production at each site. The study was conducted on sandy soils in Niger, West Africa, during the 1985 growing season. Fields were near the villages of Chikal, N'Dounga and Kala Paté, which received 223, 344 and 428 mm of total rainfall, respectively. Soils were classified as Ustic Torripsamment at Chikal, Psammentic Paleustalf at N'Dounga, and Alfic Ustipsamment at Kala Paté Water balances were calculated to the depth of maximum root penetration, which was determined at harvest by digging pits. Measurements were made using a field calibrated neutron probe and nonrecording rain gauges. Results indicate that depth of maximum root penetration was not correlated with rainfall received after planting. Seasonal crop water supply was greatest at N'Dounga, where root development was greatest. Drainage below the zone of maximum root penetration was significant at Kala Paté at 43 d after sowing, when cumulative rainfall was only 143 mm, but negligible at the other sites. Drainage could not be separated from evapotranspiration at Kala Paté 67 d after sowing and thereafter. Total evapotranspiration was 272 mm at N'Dounga and 201 mm at Chikal. Cumulative change in water storage in the zone of maximum root penetration was 0 mm at Chikal, 39 mm at N'Dounga, and 46 mm at Kala Paté. Based on the amount of water held above − 1500 kPa in the zone of maximum root penetration and profile water distribution, we conclude that water was the primary limiting constraint only at Chikal in 1985. Water supply did not appear to be the primary limiting constraint at N'Dounga and Kala Paté. Similar conclusions were obtained using the amount of root zone water held above − 100 kPa. The study suggests that water supply may not be assumed a priori to be the primary production constraint to low input millet fields such as those studied here.

Hydraulic Characteristics of Municipal Refuse

A review is made of the hydraulic conductivity and other hydraulic parameters of municipal waste. The hydraulic conductivity can be assessed indirectly from measured field parameters and water balance. A test well penetrating about 100 ft of refuse was installed and pumped for about one day at 20 gpm and 2‐1/2 days at 12 gpm. Drawdowns were measured at three observation wells and the pumped well. Difficulties were encountered during drilling and subsequent monitoring of leachate levels. The hydrogeologic parameters were computed using conventional hydrogeologic analysis. The results of a pumping test of leachate from a municipal landfill are presented. Based on the results of the pumping test, it is concluded that hydraulic conductivity of municipal refuse is about 10-3cm/s. It is also concluded that pumping of leachate from a municipal landfill is feasible for control of leachate release to ground water.

Chi river basin irrigation demand model

The calculation of irrigation demands and return flows is an essential component of the Chi Basin (Northeast Thailand) simulation model. The irrigation demand model is based on a simple field water balance so does not use the concept of effective rainfall. The paper describes the structure of the model. A sensitivity analysis on the model output is described.

Modelling soil water dynamics in the unsaturated zone — State of the art

This paper reviews the principles underlying water dynamics in the unsaturated zone and gives an overview of simulation modelling of soil water flow in the unsaturated zone. The basic relations describing kinetics of flow and governing equations of flow in the unsaturated zone are presented in a general form considering unsteady multidimensional anisotropic and nonhomogeneous flow in the presence of sinks/sources. The influence of overburden potential, characterizing swelling soils, on water transport through the unsaturated zone is discussed. Outlines of thermally-induced water flow are presented with an extension to the specific case of frozen soils. Complex relationships describing the hydrological system are reduced into the one-dimensional vertical flow cases, for which the mathematical models are defined. The entire model has the form of a set of partial differential equations together with auxiliary conditions, that describe the system's geometry, parameters, boundary conditions and in case of transient flow also the initial conditions. Simulation is defined as operation with such a mathematical model. Numerical approximations to solve governing equations of unsaturated water flow are emphasized. Recently-introduced numerical methods are discussed pointing out their advantages and limitations. Atmospheric boundary conditions of the modelled system are described with a maximizing procedure of the flux through the soil-air interface. Several options to define lower boundary conditions are discussed and a special type of lower boundary condition is given for the case that unsaturated flow is coupled with a regional groundwater model. Simulation models require data concerning input, calibration and verification. The current status of collecting model parameters is discussed as well as measurement of common verification data, i.e. phreatic surface, matric head, water content and actual evapotranspiration. Preferential flow of water through unsaturated soil has considerable consequences for simulating the field water balance. The attempts to simulate such hydrological systems are also evaluated. Some transient flow problems are affected by hysteresis. Successful attempts to build hysteresis into dynamic simulation models are still scarce, though recently a number of solutions have been presented. Finally, several practical examples of simulation of flow problems are presented. These examples are taken from everyday water management practice and document the wide range of applicability of simulation models.

Improving irrigation management by modelling the irrigation schedule

Three different treatments on corn, grown in Egyptian soil with shallow water table, on a cracked clay-loam soil subjected to swelling and shrinking, and in soil with a shallow water table have been evaluated using the simulation model SWATRE. With this field water balance model the in- and outgoing water fluxes, the soil moisture profile and the water-table depth of the three irrigation treatments monitored were simulated daily throughout the 1983 growing season. For validation the simulated water-table depths were compared to the observed water-table fluctuation. The validated field water balance model was then used to evaluate a number of hypothetical irrigation schedules in order to improve the actual irrigation practice. The simulation runs indicated that the water-table contribution through capillary rise varies between 25 and 30% of the actual crop water consumption, and that this amount is barely affected by the screened irrigation schedules. In addition it was found that plant transpiration and yield respond accurately to modifications in the irrigation timing applied.

Soil evaporation: test of a practical approach under semi-arid conditions.

The role of soil evaporation in the field water balance is briefly reviewed. With an increasing demand for improved soil and water management, the common practice of combining evaporation with transpiration into a single term, i.e. evapotranspiration, is no longer justified. The approach described in this paper combines practical experience with computer modelling. Bare field soils evaporate at a potential rate only during one or a few days after rainfall. Thereafter, evaporation is reduced due to drying of the soil surface. Both deterministic and parametric modelling often show a roughly linear increase in cumulative evaporation with the square root of time. Theoretically, this holds only if the potential evaporation is constant. This is not the case in some climates: daily potential evaporation rates commonly fluctuate between 1 and 6 mm day-1 or more in temperate climates and in some (sub)tropical climates. In such cases it appears that cumulative actual evaporation relates better to the square root of cumulative potential evaporation than to the sqaure root of time. Evaporation can be described then with a simple equation containing only one soil parameter. The latter can be easily measured, even in tilled fields, with a fast and cheap microlysimeter technique. This practical approach is illustrated with measurements in the African Sahelian zone as well as in the Netherlands. (Abstract retrieved from CAB Abstracts by CABI’s permission)