Phosphorus and Potassium Rate and Placement in Upland Cotton.

Four upland cotton (Gossypium hirsutum) field studies were conducted in Virginia and North Carolina to evaluate preplant phosphorus (P) and potassium (K) management strategies over the 2013 and 2014 growing seasons. Research objectives were to: 1) determine impacts of P and K rate by 2X2 banding and deep placement delivery methods; and 2) compare 2X2 banding and deep placement of complete N-P-K-S blends to current nutrient management practices. The fluid fertilizer application methods were 2X2 banding (5 cm beside and 5 cm below the seed) at planting, and deep placement of P and K blends during strip tillage in bands at depths of 15, 23, and 30 cm. Crop establishment, early season growth, petiole nutrient concentrations during the bloom period, and lint yield were measured. Nine treatments were replicated four times in a randomized complete block design at each site; which included an unfertilized control, granular broadcast fertilizer control, liquid P starter control (ammonium polyphosphate solutions), and three rates of P and K applied in each a 2X2 band and deep placement. Results indicate that nitrogen (N) and P levels in cotton petioles are inversely related. The unfertilized control with no N or preplant P had elevated P concentrations during the first week of bloom with 3,564 mg P/kg dry tissue, whereas plots receiving side-dress N and preplant P ranged from 1,914-2,338 mg P/kg dry tissue at locations 1 and 3. The unfertilized checks also had the shortest plant heights, being significantly lower than all fertilized treatments during 12 out of 18 sampling intervals over locations 1, 3, and 4. At location 1, 2X2 banding increased lint yields producing 2,244 kg lint/ha, while deep placement yielded 2,082 kg lint/ha respectively during 2013.