Effect of subirrigation on the subsurface crop environment and crop production

Abstract

Subirrigation of summer squash using a fluctuating water table was conducted in 12 lysimeters containing undisturbed soil cores. The soil consisted of a 45-cm depth of sandy loam topsoil and a sandy clay subsoil. The study consisted of four treatments with three replications. Pour levels of available soil water depletion between irrigations were used as the treatments. The levels of depletion were 10 percent, 30 percent, 50 percent, and 70 percent. Each treatment was irrigated by raising the water table to within 15 cm of the soil surface for the time required to saturate the soil at that depth; then the water table was lowered to the bottom of the lysimeter. An automated shelter covered the lysimeters during rainfall. Oxygen diffusion rates, soil air composition, and soil water potentials were measured. Daily soil temperatures, air temperature, wind speed, solar radiation, and relative humidity were also measured. Oxygen diffusion rates were related to the water content in the soil. A well defined relationship was not established in the coarse textured soil. Yield for the treatment having 50 percent of the available soil water depleted was 50 percent higher than for all other treatments. Water use efficiency and plant efficiency were also highest for this treatment. Dry matter production was highest when only 10 percent of the available soil water was depleted between irrigations. The statistical significance for each of the four factors were (1) yield, 0.20 level; (2) water use efficiency, 0.35 level; (3) plant efficiency, 0.05 level; and (4) dry matter production, 0.01 level. Oxygen diffusion rates were used to determine an oxygen diffusion deficit. The oxygen diffusion deficit was summed with the product of the potential evapotranspiration and the soil water potential and related to crop yield.