ABSTRACT

A common practice in areas with limited water supplies is to irrigate more uniformly and to spread a small amount of water over bigger areas. The main dilemma under these water-limited conditions is to decide between two irrigation strategies. The first is to design for a smaller flow rate and irrigate more land resource, or the second is to reduce the irrigated area and apply the flow rate that is closer to the higher potential yield. The objectives of the study were 1. To determine the optimum design capacity for cotton irrigated with a subsurface irrigation system in the Saint Lawrence area of Texas. 2. Determine the effect of different row spacing and patterns on the optimum capacity. Crop production functions for different cotton row spacings (ultranarrow, 30, and 40 in) and two planting row patterns (1 planted and 1 skipped, and 2 planted and 1 skipped) were obtained from literature and then used to conduct an economic analysis to obtain the optimum water allocations for West Texas. The crop production function obtained for this study showed a linear yield response as water allocations increased. When fixed and variable costs were included in the net return function, returns above breakeven were achieved when seasonal water allocations greater than 1.9 GPM/ac or with 23.3 inches per acre per season (including rainfall, pre-season irrigation and in-season irrigation) was considered. The ultranarrow (UNR) produced the highest net returns followed by the 30 and 40 in row spacings respectively.