Source and Timing of Nitrogen, Potassium, and Sulfur Sidedress Applications in Virginia Cotton.

Five upland cotton field studies were implemented in Virginia and North Carolina to: 1) establish an optimal nitrogen (N) fertilizer rate and timing; 2) agronomic evaluation of potassium sulfate coated urea; 3) assess the value of side-dressed potassium fertilizer on mitigating potassium deficiencies observed during the mid to late bloom period in upland cotton production. A total of 16 fertilization treatments were applied in 2012 using urea ammonium nitrate (UAN) solutions, granular urea and potassium (K) sulfate coated urea (KSCU) formulations, along with foliar applied potassium nitrate. Only fourteen treatments were implemented in 2013 with a greater emphasis placed on N rate and KSCU formulations. Side-dress N applications were applied at 1^st square and 1^st bloom, with petioles and leaves being sampled at the 1^st and 4^th weeks of the bloom period. Petiole samples were analyzed for total N, K, and sulfur (S) in 2012. In, 2013, petiole and tissue samples were collected with petioles being analyzed for nitrate-N, total N, K, and S and a complete nutrient analysis completed on the tissue samples. In 2012, petiole N was strongly correlated to side-dress N rates during the 1^st week of bloom with R²  values of .95 and .84 at locations 1 and 2 respectively. Side-dress N rates were weakly correlated to N concentrations by the 4^th week of bloom during 2012. Only location 2 responded to the added sulfur from the potassium sulfate coated urea during 2012; while potassium concentrations in the petiole were not affected at either location. In 2013, initial data show N rates applied at 1^st square correlated to petiole nitrate levels during the 1^st week of bloom with R² values of  .78 and .59. Petiole results from the early bloom period are more responsive to side-dress N applications and were a stronger predictor of yield during 2012. The high correlations of N rates and lint yield to petiole N levels during the first week of bloom show promise as an in-season N management tool.