Developing and Evaluating some Derived Models for Modeling Simultaneous Water and Nitrogen Deficit Stress

Water and nitrogen are the most important effective limiting factors for agricultural production in arid and semi-arid regions. Therefore, determining the amount of root water uptake under simultaneous water and nitrogen deficit stress conditions can play a key role in farm water management particularly in saving water and fertilizer with the purpose of maximum crop yield and consequently the maximum economical profit. The objective of this research was to introduce and evaluate derived models under simultaneous water and nitrogen deficit stress conditions and consequently calibrating their parameters for basil. In order to do so, derived models from the composition of Mitscherlich-Baule (MB) for nutrients stress conditions and models of Feddes et al., (F), van Genuchten (VG), recommended exponential (EXP) and Homaee et al., (H) for water stress conditions and also the composition model of Liebig-Sprengel (LS) for nutrients and model of Feddes et al., (F) for water stress conditions were presented and evaluated. This experiment was conducted with four irrigation water quantity levels including 120, 100, 80, and 60 percent of crop water requirement and four nitrogen fertilizer levels including 100, 75, 50, and zero percent of fertilizer requirement based on soil fertility test with three replicates. The results indicated that among the evaluated models, based on calculated statistical indices, the derived model of MB-EXP, MB-F, MB-VG, and MB-H had the best fitting on the measured data respectively.