COTTON YIELD AND GRADE RESPONSE TO NITROGEN APPLIED DAILY THROUGH A SUBSURFACE DRIP IRRIGATION SYSTEM

Nitrogen is typically applied to cotton (Gossypium hirsutum L.) in two or three split applications, however, with subsurface drip irrigation (SDI), nitrogen can be applied daily. The major objective was to show yield and grade response of cotton where nitrogen was applied daily through a SDI system at two nitrogen application strategies compared with overhead sprinkler (SP) and non-irrigated (DRY) regimens. The SDI system provided daily irrigation and nitrogen to a randomized block design with three irrigation levels (100%, IL1; 75%, IL2; and 50%, IL3); two nitrogen levels, N1 and N2, (67 and 101 kg ha -1); two drip tube lateral spacings, IR and AM (individual row = IR, alternate row middles = AM), with three replications per treatment. Nitrogen was applied in split applications to the SP and DRY areas in a randomized block design. Cotton was planted following peanuts during the 1999 and 2000 growing seasons on a Tifton sandy loam soil (fine -loamy, kaolinitic, thermic Plinthic Kandiudults). In 1999, there was a 6% lint yield increase for N2 (total lint: 1484 kg ha -1), but there was no lint yield difference with nitrogen levels in 2000 (total lint: 1280 kg/ha). There was no yield difference with drip tube lateral spacing or irrigation level except at IL3 (50%) in 1999. Lint yield was higher in both the SDI and SP compared with the DRY regime. Differences within grade parameters were not consistent across years for micronaire, fiber strength, or fiber uniformity with respect to nitrogen applied or irrigation system. Overall, the application of nitrogen on a daily basis with SDI had the same lint yield and grade compared with SP and higher lint yield than the DRY. The lower nitrogen rate (N1) had the same yield as the higher nitrogen rate (N2) which suggests that lower nitrogen rates may be appropriate when using SDI.