Exploring Options for Enhancing Water Stress Responses of Corn (Zea mays L.) in RZWQM2.

Enhancement of agricultural system models for more accurate simulations of water stress responses of crops can improve their applications in limited water management. Currently, the crop system model RZWQM2 use a ratio of potential root water uptake (supply) to potential transpiration demand as a water stress factor (WSDef) that modulates plant growth processes. We tested two progressive modifications of the WSDef (WSI1 and  WSI2) in the DSSAT-CSM-CERES-Maize (v 4.0) module embedded within the RZWQM2 model for simulating response of corn to different levels of water and compared with the use of current factor. WSI1 was a modification of SWFAC factor for photosynthesis related processes in RZWQM2 using the daily potential root water uptake (TRWUP) calculated by Nimah and Hanks (1973) approach, and WSI2 was with accounting for stress due to additional heating of canopy from unused energy of potential soil evaporation in both the supply and demand terms of the WSI1. These factors were evaluated on the data for corn grain yield, biomass, soil water and canopy cover from multiple water-level experiments conducted at Greeley, Colorado from 2008 to 2011; irrigated and rainfed corn at Akron, Colorado; and irrigated corn at Gainesville, Florida, on different soil types. The stress factors, WSI1 and WSI2 were found to be slightly superior to WSDef in simulations of grain yield and biomass in all the above experiments. In general, when WSI1 and WSI2 gave comparable simulations of grain yields, WSI1 simulations of biomass and LAI were less accurate than WSI2.