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Title:   Author  item
                                            Ma, Liwangitem
                                            Nielsen, Daviditem
                                            Ahuja, Lajpatitem
                                            Malone, Robert

                                                         - *Rob*item
                                            ANAPALLI, S - COLORADO STAT UNIVitem
                                            Rojas, Kennethitem
                                            Hanson, Jonathanitem
                                            Benjamin, Joseph
  Submitted to: Transactions of the ASAE
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/14/2003
                                    Publication  Date: 10/10/2002
                                    Citation: MA, L., NIELSEN, D.C., AHUJA, L.R., MALONE, R.W., ANAPALLI, S.S., ROJAS, K.W., HANSON, J.D., BENJAMIN, J.G. EVALUATION OF RZWQM UNDER VARYING IRRIGATION LEVELS IN EASTERN COLORADO. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 2002. v. 46. p. 39-49.Interpretive Summary: The central Great Plains is an area of widely varying precipitation and soils. Corn provides an alternative crop to winter wheat grown in the traditional wheat-fallow system. Models of corn development and yield could  be used to predict corn productivity under varying soil and weather conditions to help producers assess risk in changing cropping systems to one which includes corn production. To use the Root Zone Water Quality Model (RZWQM) for this purpose requires that the model be calibrated and validated for central Great Plains conditions. This study used data sets from three years of corn grown at Akron, CO to calibrate and validate RZWQM under several irrigation levels. The model responded well to irrigation treatments and weather conditions, providing reasonable estimates of plant height, leaf area index, aboveground biomass, corn water use, and grain yield. The calibrated model should be useful for estimating corn production under varying water availability in the central Great Plains.
                                Technical Abstract: The ability to predict and manage crop growth under varying available water conditions are of vital importance to the agricultural community since water is the most important limiting factor for agricultural productivity in semi-arid regions. This study evaluated an agricultural system model, the USDA-ARS Root Zone Water Quality Model (RZWQM), for its ability to simulate the responses of corn (Zea mays L.) growth and yield to various levels of water stress. Data sets collected in 1984, 1985, and 1986 in northeastern Colorado were used for model evaluation. Three irrigation levels were imposed in 1984 and four levels in 1985 and 1986. Measurements included soil water content in 1985, leaf area index (LAI) and aboveground biomass in 1984 and 1985, and corn yield and plant height in 1984, 1985, and 1986. The RZWQM was calibrated for the lowest (driest) irrigation treatment in 1985. Overall, the model responded well in all three years to irrigation treatments and weather conditions. Prediction of plant height was adequate in 1985 and 1986. Although biomass was reasonably predicted in early and late growing seasons, it was over-predicted during the middle growing season in both 1984 and 1985. Maximum LAI and plant height were over-predicted in 1984, however. Total soil water storage was well predicted in 1985, as was evapotranspiration during the crop growing season. Yield predictions were within 1% to 35% of measured values for all three years. Even with a low prediction of yield in 1986, the model correctly simulated the relative increase of yield with irrigation amount. Therefore, once RZWQM is calibrated for a location, it can be used as a tool to simulate crop production under different irrigation levels and as a guide to optimize water management.


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