Submitted to: Advances in Agricultural Systems Modeling
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2014
Publication Date: 12/1/2014
Citation: Anapalli, S.S., Ahuja, L.R., Ma, L., Trout, T.J. 2014. Modeling the effects of irrigation frequencies, initial water and nitrogen on corn yield responses for best management. Advances in Agricultural Systems Modeling. pp 26-52.
Interpretive Summary: When in the semi-arid climate of Colorado and surrounding regions, farmers rely on irrigation water supply for dependable returns from corn farming, pressures on freshwater keep rising from the expanding needs of many other competing human enterprises. In this context, to enhance water use efficiency in corn production, we developed crop water and nitrogen production functions (CW-NPFs) that take into account change in water supplies and demands due to varying weather across crop seasons, initial water stored in the soil at planting, irrigation frequency and N rates at Greeley, Colorado. Among the intervals of irrigations simulated, a 7-day frequency was found to be optimum taking into account yield responses, N uptake and recovery efficiencies, and residual N in the soil at harvest in the limited water irrigation scenario. Hypothetically imposed (low, medium, average and high) initial water in the soil at planting was found to increase crop responses to irrigation in the climate of the location. Hence, soil-crop-residue-water management practices to improve soil water storage in the soil during the fallow periods can help in increase corn production with limited water irrigation. Taking into account the yield responses to N under different irrigation scenarios, optimum N rates for optimum corn yield for irrigations levels of 40, 50, 60, 70, 80, 90 and 100 % ET recharge were 50, 100, 100, 150, 200, 200 and 200 kg ha-1. N applications above these N rates were found to have lower Irrigation water use and nitrogen use efficiency and potential for higher residual soil N at harvest that can pollute the environment and natural resources later.
Technical Abstract: Competing demands for fresh water resources necessitate adaptation of limited water irrigations in agriculture. In this context, the Crop Water Production Functions (CWPF) used in limited water irrigation management need to integrate the effects of climate, initial soil water content at planting, and amounts and frequencies of irrigations, and nitrogen (N) levels. Crop yield responses to both water and N allocations throughout the growth period are termed as Crop Water and N Production Functions (CW-NPFs). Field experiments integrating all these factors and their interactions on crop responses are lacking. The objective of this study was to explore ways of enhancing the crop irrigation water use efficiency (IWUE) and N use efficiency (NUE) of applied water and N, with minimum residual soil and leached N. The study was an RZWQM2 model extension of the field experiments conducted at the Limited Irrigation Research Farm near Greeley, CO during 2008-2011. We simulated the crop at varying initial soil water levels (Iw), irrigation amounts and frequencies, and N levels. Irrigation water was applied to supplement rainfall in order to meet the potential crop evapotranspiration (ET) demand at 0 to 100% levels at 10% intervals. These irrigation amounts were applied at irrigation frequencies of 3, 7, 10 and 14 days. N application rates were 0, 50, 100, 150, 200, 250 and 300 kg ha-1. Corn grain yield was higher at higher irrigation frequencies (smaller intervals). Yield was also higher at higher Iw values; this was also reflected in Yield-ET and Yield-T relationships. CW-NPFs differed greatly with N application rates. NUE increased in response to irrigations up to 60% ET recharge but plateaued thereafter with further irrigations. For higher IWUE and NUE with minimum soil residual N at harvest, optimum N rates for corn yield for irrigations levels of 40, 50, 60, 70, 80, 90 and 100 % ET recharge were 50, 100, 100, 150, 200, 200 and 200 kg N ha-1, respectively. Resources were not limiting, for optimum grain yield, 7-day irrigations to recharge 90% ET losses and N at 200 kg ha-1 were the best management choice simulated. The results of the study will be used to develop site-specific recommendations for efficient water and N management.