On‐Farm Winter Wheat Response to Nitrogen‐, Phosphorus‐, Potassium‐, and Sulfur‐Rich Strips in Oklahoma

CORE IDEAS: Thirty‐two percent of the locations had an increase in grain yield with increased nutrient inputs. Wheat response to additional N was potentially due to underestimated yield potential or N losses attributable to ammonia losses, immobilization, leaching, or environmental conditions. Response of wheat to additional P was likely a result of underapplication of P fertilizer, especially on low‐pH soils Winter wheat grain yield response to K fertilization in the high soil test K environment was potentially due to enhanced vegetative growth of wheat during drought conditions. Soil test SO₄–S levels were adequate to produce grain yields above estimated yield goals. Temporal and spatial variations both play a major role in nutrient requirements and availability. This study was conducted to highlight variability in nutrient requirements across landscapes, soil types, and environments, and to evaluate if Oklahoma producers’ current fertilization management schemes for nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) are maximizing winter wheat (Triticum aestivum L.) grain yields. Nutrient‐rich strips of N, P, K, and S and a farmer‐practice strip were established in 2011–2012 and 2012–2013 at 42 and 40 locations in Oklahoma, respectively. Urea (46–0–0), triple super phosphate (0–46–0), potash (0–0–60), and gypsum (19% S) were used as sources of N, P₂O₅, K₂O, and S, respectively. The N‐, P‐, K‐, and S‐rich strips were applied with an additional 105 lb N/acre, 105 lb P₂O₅/acre, 119 lb K₂O/acre, and 43 lb S/acre, respectively, on top of the farmer's fertility practice. Surface (0–6 inches) and subsurface (6–12 inches) soil samples were collected prior to nutrient applications. Of the 82 nutrient‐rich strip locations established, 59 were harvested. Winter wheat grain yield was increased with the addition of N at seven locations, P at nine locations, and K at eight locations. No yield response to additional S fertilizer was observed at any location. A total of 19 locations, 32%, responded to the addition of N, P, or K, demonstrating that there is opportunity for Oklahoma wheat producers to increase yield through improved nutrient management.