Water Flux below the Root Zone vs. Drip‐Line Spacing in Drip‐Irrigated Corn

Abstract

AbstractUse of microirrigation (drip) is increasing, prompted by factors such as a greater ability to control losses of water and nutrients from the root zone. The cost of drip can be reduced by using wider drip‐line spacings. Our objective was to evaluate water flux below the root zone (1.5‐m soil depth) with a subsurface drip irrigation system having drip‐line spacings of 1.5, 2.3, and 3.1 m near Colby, KS. The soil is a deep silt loam that formed in loess. The crop was corn (Zea mays L.), planted in rows spaced 0.76 m apart. Water flux at the 1.5‐m soil depth was determined in five treatments (Trt.): 1.5‐m spacing, full irrigation; 2.3‐m spacing, 67% of full irrigation; 2.3‐m spacing, full irrigation; 3.1‐m spacing, 50% of full irrigation; and 3.1‐m spacing, full irrigation. With full irrigation, irrigation plus effective rain equaled calculated corn evapotranspiration (ET). Tensiometers were placed below the drip line and at increments of 0.4 m from the drip line at soil depths of 1.4 and 1.7 m. Water flux was calculated by using a hydraulic conductivity (K) vs. matric potential (ψm) relationship, ψm data from tensiometers within the corn plots, and Darcy's equation of water flow. In‐season water fluxes below the root zone (1.5 m) were 51, 118, and 124 mm at drip‐line spacings of 1.5, 2.3, and 3.1 m, respectively. In 1990, corn grain yield was not significantly affected by spacing. In 1991, with drier initial soil‐water conditions, corn yielded significantly less grain at spacings of 2.3 m (11.5 Mg ha‐1) and 3.1 m (10.7 Mg ha‐1) than at a drip‐line spacing of 1.5 m (13.1 Mg ha‐1). If spacing between drip lines is increased beyond 1.5 m in the silt loam soils of western Kansas, there would be an associated increase in internal drainage from the root zone and decrease in corn yields.