Modification of a maize simulation model under different water, nitrogen and salinity levels

Irrigation, salinity and nitrogen (N) are the three major limiting environmental factors inmaize yield potentials especially in arid and semi-arid regions. An integrated water and N MaizeSimulation Model (MSM) was modified for salinity conditions using 2009-2010 fieldexperiments data in southwest of Iran. Irrigation levels were: I1=1.0ETc+0.25ETc as normalleaching amount, I2=0.75I1 and I3=0.5I1, salinity of irrigation water: S1=0.6, S2=2.0 and S3=4.0dS m-1 and N fertilizer rate: N1=0, N2=150 and N3=300 kg N ha-1. Data of the first and secondyear were used to calibrate and validate the modified model, respectively. The MSM model wasmodified by including the combined effects of water and salt stresses using different wateruptake functions. Furthermore, N uptake via mass flow process was also modified. By thismodification, the soil salinity was also estimated by the model. Calibration/validation resultsshowed that the water uptake function of Homaee and Feddes led to a better estimation of allparameters than those obtained by other water uptake functions. Based on the NRMSE and dindices, the modified MSM model presented a very good to fair estimation of soil water content,salinity and N, evaporation, transpiration, evapotranspiration, leaf area index, total dray matter,N uptake and grain yield. Besides, under saline irrigation water there was much higher risk tothe groundwater contamination by nitrate leaching.