Evaluation of a model for irrigation management under saline conditions : II. Salt distribution and rooting pattern effects

Increasing salinity is a significant factor affecting the future agricultural productivity in semiarid irrigated regions of the world. Computer simulation models, which can be used to evaluate the consequences of differing management strategies on crop yield and salt distribution in the soil profile, would be valuable. Simulated results from models must be compared with measured results from field experiments to establish their validity. The simulated salt distribution from the ENVIRO-GRO model were compared with measured distribution at the end of they growing season from an experiment that had treatment variables of irrigation water electrical conductivity (EC) of =1.7, 4.0, 5.0, 8.0, and 10.2 dS m -1 and average irrigation intervals of 3.5, 7, 14, and 21 d. Root distribution is an input variable to the model. Therefore, a second objective of the study was to test the sensitivity of the model results to the root distribution. In general, the agreement between measured and simulated salt distributions were better for the longer than for the shorter irrigation intervals. For the shorter irrigation intervals, the measured salt concentration near the soil surface was greater than was simulated. This result is explained by the fact that the model does not separate the transpiration (T) from the evaporation (E) component of evapotranspiration (ET), and assumes that all water is lost by T. The E:T ratio would be expected to increase as the irrigation frequency increases, and E would carry salts to the soil surface. Except for nonsaline conditions with frequent irrigation, the simulated yields were increased by having a deeper root distribution. The effect of a deep root system was greater for the longer irrigation interval when the water storage capacity within the root zone becomes more important.