Source and Timing of Nitrogen, Potassium, and Sulfur Side-Dress Applications in Virginia Cotton

Two field studies were implemented in Virginia to evaluate 1) nitrogen fertilization practices on petiole nitrogen concentrations and lint yield and 2) mitigation of late season potassium deficiencies using potassium sulfate coated urea (37-0-9-3S). A total of sixteen nitrogen fertilization treatments were applied using urea ammonium nitrate solutions, granular urea formulations, and foliar applied potassium nitrate at different nitrogen rates and timings. Fertilizer was applied at first square and first bloom with petioles being sampled at the 1^st and 4^th weeks of the bloom period. Petioles were sampled from the fourth fully unfurled leaf down the main stem and 24 petioles were collected from the 1^st and 4^th rows of four row plots. Petioles were analyzed for percent nitrogen, potassium, and sulfur.  There was a strong linear relationship between nitrogen rate applied at first square and percent nitrogen in petioles during the 1^st week of bloom with R² values of 0.96 and 0.84 at locations 1 and 2, respectively. At the 4^th week of bloom nitrogen applied at first square weakly predicted nitrogen concentration in cotton petioles with R² values of 0.33 and 0.52 for locations 1 and 2, respectively. Nitrogen concentrations fell from 1.7-3.85% during the1st week of bloom to less than 1% at both locations during the 4^th week of bloom. Only location 2 responded to the added sulfur from the potassium sulfate coated urea during 2012.  Potassium concentrations in the petiole were not increased with soil applied potassium in the form of potassium sulfate coated urea at either location. However, there was a difference in potassium concentrations between locations at the 1^st week of bloom. This was most likely due to different rates of potassium applied preplant based on soil test recommendations.