Computer simulation of the irrigation potential of selected low water holding capacity soils
A soil-moisture program developed by Shaw has been used to determine a weighted seasonal stress index. This weighted seasonal stress index was used in a regression equation to estimate corn yield. By including an irrigation cycle in the program, the response to irrigation was simulated;Eight sites were chosen to evaluate the effect of irrigation on corn yield on low moisture-capacity soils in Iowa. The average yield increases ranged from 822 Kg/ha at Cedar Rapids to 3261 Kg/ha at Doon. The greatest irrigation amounts were applied in northwest Iowa (Doon), and the least amounts were applied in eastern Iowa. The soil-moisture program was run for two soils, Webster and Dickman, in southwest Minnesota (Lamberton). On Dickman sand, the average yield increase due to irrigation was 4518 Kg/ha, and for the Webster soil, the average yield increase due to irrigation was 2144 Kg/ha;The original program was modified to represent conditions existing at the Cisne soil in Fayette County, Illinois. In the first modified program, excess moisture above field capacity gradually filled each layer until the first layer reached saturation. The average yield increase due to irrigation was 3755 Kg/ha in the program, in which starting soil moisture was at field capacity. In the same program, when saturation was assumed as the starting soil moisture, the average yield increase due to irrigation was 3429 Kg/ha. In the second modified program, daily rainfall filled each layer to saturation and a subroutine was constructed to allow for downward movement for water until field capacity is reached. For the situation when the starting soil mositure was assumed to be at field capacity, the average yield increase due to irrigation was 4678 Kg/ha. When the starting soil moisture was assumed to be at saturation, the average yield increase due to irrigation was 4564 Kg/ha. The original soil moisture program was run in order to represent what would happen if the soil had an excellent drainage system. The average yield increase due to irrigation was 4827 Kg/ha;Data and information about water supply and use were also reviewed to evaluate the possibility of irrigation of low water-holding capacity soils in Central Iowa. It concluded that irrigation is possible if an appropriate water resources plan was in operation for this area. Such a plan would include storing seasonal surface water and withdrawals from deeper aquifers in the region.