Irrigation and Sidedress Nitrogen Management of Cotton in a Well-Drained Sandy Soil.

North-Central Florida is characterized by entisol soils which have excessive permeability, resulting in the possibility of rapid soil water depletion or nutrient leaching following high intensity precipitation events. This results in the possible need for both supplemental irrigation and in season nutrient applications during a single growing season. The primary objective of this research is to assess the possible interactions between varying irrigation and side-dress nitrogen (N) applications in cotton. A field study was initiated in 2015 at the University of Florida’s Plant Science Research and Education Unit in North Central Florida (29° 24' 38" N, 82° 10' 12" W). Irrigation and sidedress N treatments were randomized in split plot arrangement with irrigation as the whole plot and sidedress N rates as the sub-plot. Irrigation treatments included: 1) 100% of plant available water (PAW) replacement; 2) a treatment consisting of 50% of PAW replacement until first flower and then 100% of PAW replacement; 3) 50% PAW replacement for the entire season; and 4) a rainfed control. Sub-plots consisted of NH₄NO₃ source applied at first square and flower at 0, 22, 34, and 45 kg N ha^-1 per application. In 2015, there was no irrigation by nitrogen interaction on lint yield, and irrigation applied relatively early in the growing season (< 60 DAP) also had no effect on lint yields. Sidedress N applications greater than 45 kg N ha-¹ did not result in an increased amount of plant N uptake or lint yield. These results indicate that yield maintenance can occur with reduced amounts of early season irrigation, and sidedress N applications of 22 kg ha^-1 at first square and first flower.