Investment Returns from Three Sub-surface Microirrigation Tubing Spacings

Abstract

Sub-surface microirrigation (SMI) tubing costs make up 33 to 60% of total purchase and installation costs of the system, depending on tubing spacing. Purchase and installation costs of SMI systems can be lowered by $290/acre by increasing tubing spacing from 3 to 9 ft. Yields may be reduced due to less uniform placement of water in the crop root zone. The net present values (NPVs) of three SMI tubing spacings were estimated for systems irrigating corn (Zea mays L.) and peanut (Arachis hypogaea L.). The analysis included investment costs for purchasing and installing the irrigation system but did not include water source development costs. Irrigated yield responses and irrigation applications came from field experiments conducted from 1986 to 1995 at Suffolk, VA, on an Uchee loamy sand (loamy, siliceous, thermic Arenic Hapludult) with inclusions of Emporia loamy sand (fine-loamy, siliceous, thermic Typic Hapludult). The 6-ft tubing spacing had the highest NPV of $14/acre. The low NPV indicates it is unlikely to be profitable when water source development costs are included. NPVs of 3-ft and 9-ft spacings were -$28 and -$104/acre, respectively. Six-foot spacing had lower yields and lower investment costs than 3-ft spacing. Increasing the proportion of corn in the rotation lowered the advantage of 6-ft spacing. Higher peanut and corn prices or reduced tubing prices narrowed the difference in NPVs between 3-ft and 6-ft spacings. Six-foot tubing spacing results in highest returns when SMI is used for corn-peanut rotations on sandy soils in Virginia/North Carolina.