SUBSURFACE DRIP IRRIGATION LATERAL SPACING AND MANAGEMENT FOR COTTON IN THE SOUTHEASTERN COASTAL PLAIN

Abstract

The cost of drip irrigation can be reduced by using both wider lateral spacings and the same laterals formultiple years, as with subsurface placement. Multiple, low-rate fertilizer and water applications may reduce N fertilizerneeds by improving efficiency and limiting the potential for leaching. The combination of these technologies may makedrip irrigation of cotton profitable. Four years of continuous cotton and two years of cotton rotated with peanut wereevaluated. Two subsurface drip irrigation lateral spacings (every row, 1 m, and alternate furrow, 2 m) and threesidedress-nitrogen methods (STD, single application of 112 kg/ha; INC, 112 kg/ha in five equal applications; and GOS,applications determined by GOSSYM/COMAX) were evaluated for cotton during 1991-1994. Two of the sidedressnitrogenmethods (STD and GOS) were evaluated for a rainfall-only treatment. Lint yields did not differ between thelateral spacings in any year. Yields for irrigated treatments were 16 and 65% greater than rainfall-only yields in 1992 and1993, respectively. The GOSSYM/COMAX-managed nitrogen treatment received 30% less nitrogen fertilizer than othertreatments, but had similar lint yield. Several fiber physical properties were affected by irrigation and nitrogen, but theseeffects were small and inconsistent. For continuous cotton, or cotton rotated with peanut, the wider lateral spacing ispreferred to the every-row spacing because of its lower initial cost (about 30%). The combination of lower system cost,longer system life, and lower N-fertilizer requirements could make subsurface drip irrigation of cotton profitable forsoutheastern Coastal Plain soils, and reduce the potential for ground water contamination.