Evaluation of Soil Phosphorus Index for No-till Wheat Production in Oklahoma.

Phosphorus deficiency in no-till winter wheat production can result in drastically reduced yields in central Oklahoma.  Current sampling methods and fertilizer recommendations for phosphorus are based on tillage practices and the incorporation of fertilizers such as phosphorus that are relatively immobile in the soil. This study was established to evaluate the yield response of hard red winter wheat (Triticum aestivum L.) to phosphorus fertilizers in both sufficient and deficient soils, the current Soil Phosphorus Index, established soil sampling method, as well as the soil test index for phosphorus in no-till systems.

The effect of surface applied triple super phosphate fertilizer on dryland no-till winter wheat was investigated at six site locations throughout north central Oklahoma during the 2014-2015 growing season.  Two of the locations were located in Waukomis, OK on a Grant silt loam (fine-silty, mixed, superactive, thermic Udic Argiustolls) and a Port silt loam (fine-silty, mixed, superactive, thermic Cumulic Haplustolls).Three sites were located in Red Rock, OK on a Bethany silt loam (fine, mixed, superactive, thermic Pachic Paleustolls) and a Kirkland silt loam (fine, mixed, superactive, thermic Udertic Paleustolls). The Stillwater site was on a Huska Silt Loam (fine, mixed, superactive, thermic Mollic Natrustalfs). Site locations had an initial soil test index ranging from 2-68 ppm phosphorus in the top 30 cm at planting. Phosphorus was applied at rates of 0 to 112 kg ha^-1 in 11.2 kg increments at planting as a top dress treatment. Soil samples were taken pre-plant and post-harvest to a depth of 45 cm with the top 30 cm sectioned in 5 cm increments. Soil samples were extracted using Mehlich III and analyzed on an ICP. Yield response to phosphorus fertilizer will be discussed as well as the correlation between yield response and Soil Test Index for phosphorus throughout the sectioned soil profile.