CONJUNCTIVE USE OF SALINE AND NONSALINE WATERS .3. VALIDATION AND APPLICATIONS OF A TRANSIENT MODEL FOR WHEAT

A transient state model for numerical simulations of water and solute transport and plant water uptake (V-H model) was modified and applied to develop saline irrigation strategies for wheat grown in Northern parts of India. Three modifications made in the sink term were: (1) allowing for increased tolerances to salinity stress at progressive growth stages of wheat; (2) time and depth patterns of root distribution as fitted to experimental data, i.e. a logistic function for rooting depth with time and an exponential function to define root distribution; and (3) reductions in osmotic stress due to ion pair formations on concentration of soil solutions with water uptake. With these modifications, the V-H model allowed for good agreement between observed and predicted wheat yields under various conjunctive use modes of saline and non-saline water (mean square error, MSE=0.0027) as well as quantities and salinities of irrigation water over the years varying in rainfall (MSE=0.0074). Production functions for different salinity waters and their quantities are also presented. Simulations indicated higher benefits of increasing frequency with saline irrigations when the quantity of water applied for each irrigation is simultaneously reduced. Otherwise, such a practice was predicted to increase salt load in soils, thus negating the benefits through aggrevated salinity. Potentialities of using higher salinity waters for wheat production increased when such waters were introduced late in the season.