Sufficiency Level Vs. Build and Maintain Approaches to Managing Phosphorus for Crop Production.

Phosphorus fertilizer management in Minnesota is based on one of two philosophical approaches, Build and Maintain (B&M) and Sufficiency. Long-term experiments were established at six sites across Minnesota. At each site, four soil test P (STP) Interpretation Classes of Low, Medium, High, and Very High were established over a four-year period. Each STP class was split into two split-plots: one received no additional P fertilizer, and the other received 168, 101, 34 and 34 kg P₂O₅ ha^-1 in the Low, Medium, High, and Very High class, respectively. Corn grain yield and grain P removal were determined during 2015 and 2016 growing season. Overall, 2 of the 6 sites showed significant response to applied-P only in the Low and Medium soil classification classes (Becker, Crookston) in 2015. During 2016 growing season 3 of the 6 sites showed significant response to applied-P only in the Low and/or Medium STP classes (Becker, Crookston,Waseca). Grain P removal was more responsive in both growing seasons, and 4 of the 6 sites showed greater P removal with applied-P especially in the Low and Medium classification classes. The greatest response to fertilizer P was in the Low and Medium STP classes as expected. There was little to no response to applied P in the High or Very High STP classes. In both growing season, there was no evidence at any of the sites that building and maintaining a high soil test level had a greater grain yield potential than applying P fertilizer annually based on soil test level regardless what that level was. The Sufficiency Approach was just as productive with P fertilizer applied to Low or Medium soil testing P soils as higher testing P soils with or without P fertilizer applied.