Gaylord V. Skogerboe

Crop production functions and the allocation and use of irrigation water

Abstract The economically optimal depth of irrigation water to apply depends on the relationship between crop yield and water use. Past research efforts to formulate and to explain the factors influencing irrigated crop production functions have therefore been briefly reviewed. Although it is not possible to obtain a unique relationship, by considering a possible range of functions, and by understanding the factors causing variations in the form of these functions, valuable conclusions can be drawn relating to the optimal depth of water application and the relative magnitude of benefits derived from efficient water management.

Modeling salt transport in irrigated soils

Abstract This study evaluates the effects of the volume of leachate on the quality of the leachate. A numerical model of salt transport was used in the study. Field data were collected on 63 research plots located in the Grand Valley (Colorado, U.S.A.) and used to test and calibrate the model. The model was used in a series of hypothetical simulations designed to provide the required information. From the calibration of the moisture-flow model using infiltration data, soil water-content profiles, and soil water-storage change data, it was concluded that soil-water flow could be adequately modeled for the Grand Valley. The functional relations used for hydraulic conductivity and soil-water diffusivity and the method of averaging the values of the hydraulic parameters were developed during the course of the study. From comparisons of simulated and field data used in evaluating the chemistry model, it was concluded that total dissolved solids (TDS) concentrations were adequately modeled, but that individual ionic species concentrations were not. Comparison of calculated and measured data indicate that the CaSO 4 ue5f8CaCO 3 ue5f8Ca(HCO 3 ) 2 system is not properly modeled for the soil in the Grand Valley. Data for single growing season simulations using 7- and 14-day irrigation schedules and 2, 5, 20 and 40% leaching increments, coupled with data from a six-year simulation using a 14-day irrigation interval and 20% leaching increment, indicate that the salt concentration of the leachate at the bottom of the soil profile is independent of the volume of leachate.

Using a crop growth simulation model for evaluating irrigation practices

Abstract Water management decisions are dependent on crop variety, soil and climatic conditions. A properly structured plant growth simulation model which takes these factors into account can be successfully used to quantify the effects of irrigation practices on crop yields. The use of such a simulation model will be considerably less expensive and time consuming than conducting field experiments. This paper reports the results of using such a model for making important water management decisions, such as determining: (a) optimum soil moisture depletion and replenishment levels; and (b) timing and amount of irrigation during different crop growth stages.

Improvement and sensitivity analysis of the corngro model

Abstract A systematic description of the CORNGRO model is presented, highlighting those aspects of the model which have not been reported earlier. The model was modified to better simulate the corn growth process and predict the final yields. The sensitivity of the simulation results to the input values of some important environmental factors were tested. The sensitivity analyses indicate that the simulation results of the model are moderately sensitive to the soil property curves, and highly sensitive to the input values of the daily potential evapotranspiration (ETP). Also, the plant growth parameters are more sensitive to the input values of daily ETP for adequate irrigation treatments than for deficient irrigation treatments.

Ecological modelling, monitoring and implementation in irrigated agriculture

Abstract In rainfed agriculture, most of the efforts in modelling have been concerned with surface runoff; the greatest modelling capability exists for sediments, followed by pesticides, and then nutrients. In irrigated agriculture, tremendous strides have been made in modelling subsurface flows, either saturated or unsaturated flow; the modelling capability follows the order of priority for major pollutants — salts, sediments, nutrients and pesticides. Significant strides could be made by a concerted effort to combine the knowledge gained in irrigated and rainfed agricultural modelling to develop more comprehensive models. Such models combined with recent advances in the hydraulics of surface irrigation and surface irrigation scheduling will allow highly effective water quality control programs to be implemented that are a combination of technological ‘hardware’ solutions and management ‘software’ solutions.

MODELING PROCESS FOR ASSESSING WATER QUALITY PROBLEMS AND DEVELOPING APPROPRIATE SOLUTIONS IN IRRIGATED AGRICULTURE

A planning framework is presented for arriving at cost-effective solutions to water pollution problems resulting from subsurface irrigation return flows. The modeling process is demonstrated for salinity management in irrigated agriculture, which involves inflow-outflow analysis, hydro-salinity modeling, soil moisture chemistry simulation, and an optimizational analysis to arrive at the most cost-effective strategy for reducing the salt load in the groundwater reservoir or river.