Performance Analysis of AquaCrop and Hybrid-Maize Models in Estimating Crop Yield, Water Use and Plant Phenological and Physiological Variables

The simulation of crop development and growth parameters by any crop model is based on complex interactions between climate, crop and soil parameters and management practices. Given this situation, there is need of crop models that are robust in performance, simple to use, requires smaller number of input parameters that are easily available, transparent in formulation and well supported with comprehensive documentation for end users. Such two crop models including AquaCrop and Hybrid Maize were selected in this study to assess their performance in predicting maize growth and yield parameters in Nebraska. In this dissertation, four chapters addressing the following objectives are presented: The first chapter aims to assess AquaCrop model performance relative to maize canopy cover, biomass, yield, soil water content, and crop evapotranspiration under rainfed conditions, full irrigation and limited irrigation (50, 60, and 75% of FIT) regimes. The model was calibrated and validated using long-term (2005–2010) field measured data and set of calibrated parameters were developed for Nebraskan conditions. The model efficacy was evaluated for both default and calibrated parameters. In second chapter, AquaCrop was tested for predicting maize canopy cover, available soil-water, grain yield, crop evapotranspiration, and water use efficiency when grown at three different planting dates and densities under rainfed and subsurface drip-irrigated conditions in Nebraska, USA. Detailed analyses of model performance, potential reasons for the discrepancies and areas of improvements were discussed. The third chapter evaluates Hybrid-Maize performance relative to simulation of maize growth, yield, and water use parameters under full (FIT), limited irrigation (50, 60, and 75% of FIT) and rainfed conditions over six years (2005–2010) in Nebraska. The differences between model simulated and field observed crop variables were assessed and additional improvements relative to simulation of soil water balance components were suggested. The fourth chapter aims to assess the impact of climate change on maize yield in Nebraska. The calibrated AquaCrop model was used to forecast long-term (2019–2090) yield and analyze the impact of climatic variations relative to the baseline period (1983–2018) on both yearly and decadal (2020s–2090s) basis under two emission scenarios of representative concentration pathways including RCP4.5 and RCP8.5