The Impact of Irrigation and Nitrogen Rate on Yield and Fiber Quality of Determinate and Indeterminate Cotton Cultivars.

Optimizing irrigation quantity and timing at each growth stage is essential to maximizing cotton lint yield and preventing poor fiber quality. Furthermore, yield and fiber quality responses to nitrogen (N) rate and irrigation regimes are hypothesized to vary by cultivar, especially between cultivars of varying maturities and determinacies. In order to quantify cultivar response to N rate and irrigation, a study was conducted in 2012-2014 at the West Tennessee Research and Education Center (WTREC) in Jackson, TN. Two cotton cultivars [PHY 367 WRF (early determinate) and PHY 499 WRF (late indeterminate)] were subjected to six sub-surface drip irrigation regimes [combinations of rainfed to 0.5” water per week at mid-square, 0.5-1.5” per week during early bloom, and 1.0-1.5” per week during late bloom)] and two N rates (80 and 120 lb N/ac). Trial design was a split-split-plot with four replicates. The response of lint yield and fiber quality to N rate, irrigation regime and cultivar varied in each of three years due to different rainfall amount. During 2012 and 2013, PHY 499 WRF significantly out-yielded PHY 367 WRF. Also, in 2012, the 0.5”/wk mid-squaring-1.5”/wk early and late bloom irrigation regime significantly out-yielded the rainfed treatment. However, excessive amounts of rainfall relative to the 30 year normal trends for the location during 2013 and 2014 resulted in no significant yield or fiber quality differences associated with irrigation regimes. The effect of nitrogen rate was only significant during 2014, the 120 lb N/ac increased the cotton yield more than the 80 in most irrigation regimes. However, there was no consistency found in interaction between irrigation regime, N rate and cultivar to impact yield and fiber quality among 3 years of study. Additional research should be conducted to investigate this irrigation system and interactions during more normal-rainfall years.

Key words; sub-surface drip irrigation system, irrigation regimes, nitrogen rates, cotton cultivars