Crop‐water Production Functions for Sweet Corn and Cotton Irrigated with Saline Waters

The effect of irrigation water quality (salinity) and quantity on the yields of sweet corn (Zea mayscv. Jubilee) and cotton Gossypium hirsutumL. cv. Acala SJ‐2) was studied in a sandy loam (Typic Torrifluvent) soil. For each of the irrigation water salinities of Co= 1.8, 3.6 and 6.7 dS/m (for corn) and Co= 3.6, 6.7, and 10.5 dS/m (for cotton), 10 amounts of irrigation water (Q) ranging from 0.15 to 2.7 times the class A pan evaporation (Eo) were applied via trickle irrigation. Root zone soil‐water matric potential, water content, and salinity were monitored, and corn and cotton yield components were measured. Time‐averaged root zone soil water content (θ) and soil salinity (EC), as well as crop yield components (Y) were affected by both Qand Co. Results of the analyses of the crop‐water production functions suggest that increasing the amount of irrigation water may compensate only in part for the adverse effects of the salinity of the irrigation water. For corn, using irrigation water of Co= 3.6 and 6.7 dS/m, maximum ear yields were reduced by 8 and 27%, respectively, relative to the maximum ear yield obtained using water of 1.8 dS/m. For cotton, using irrigation water of Co= 6.7 and 10.5 dS/m, maximum seed cotton yields were reduced by 6.5 and 30%, respectively, relative to the maximum seed cotton yield obtained using water of 3.6 dS/m. Analysis of the Y(θ, EC) relationship for each of the corn and the cotton yield components suggested that, due to the mutual effect of θ and EC on Y, the crop response to salinity curve is affected by θ and, in general, should be described by a nonlinear concave expression rather than by the piecewise linear expression of Maas and Hoffman (1977).