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

The cost of drip irrigation can be reduced by using both wider lateral spacings and the same laterals for multiple years, as with subsurface placement. Multiple, low-rate fertilizer and water applications may r educe N fertilizer needs by improving efficiency and limiting the pote ntial for leaching. The combination of these technologies may make dri p irrigation of cotton profitable. Four years of continuous cotton and two years of cotton rotated with peanut were evaluated. Two subsurfac e drip irrigation lateral spacings (every row, 1 m, and alternate furr ow, 2 m) and three sidedress-nitrogen methods (STD, single application of 112 kg/ha; INC, 112 kg/ha in five equal applications; and GOS, app lications determined by GOSSYM/COMAX) were evaluated for cotton during 1991-1994. Two of the sidedress-nitrogen methods (STD and GOS) were e valuated for a rainfall-only treatment Lint yields did not differ betw een the lateral spacings in any year Yields for irrigated treatments w ere 16 and 65% greater than rainfall-only yields in 1992 and 1993, res pectively. The GOSSYM/COMAX-managed nitrogen treatment received 30% le ss nitrogen fertilizer than other treatments, but had similar lint yie ld. Several fiber physical properties were affected by irrigation and nitrogen, but these effects were small and inconsistent. For continuou s cotton, or cotton rotated with peanut, the wider lateral spacing is preferred to the every-row spacing because of its lower initial cost ( a:bout 30%). The combination of lower system cost, longer system life, and lower N-fertilizer requirements could make subsurface drip irriga tion of cotton profitable for southeastern Coastal Plain soils, and re duce the potential for ground water contamination.