Minnesota Long-Term Phosphorus Management Trials: The Build Period.

Phosphorus (P) fertilizer management in Minnesota is based on one of two philosophical approaches, Build and Maintain (B&M) and Sufficiency. In recent years, it is argued that higher fertilizer applications associated with the B&M approach are necessary to obtain and maintain greater production levels in today’s agricultural systems. The purpose of these trials was to establish long-term experiments that could be used to test P management strategies on soils with a defined long-term phosphorus history. Six experimental sites were located across Minnesota. At each site, a split-plot randomized complete block experimental design: whole plot treatment is the targeted or established soil test P (STP) Interpretation Class. The STP classes targeted in the whole plots are Low, Medium, High, and Very High. Soil samples were taken at a depth of 15 cm. All sites had corn-corn-corn-soybean rotation except Crookston (corn-soybean-hard red spring wheat-soybean). All sites had reached significant differences among the four established interpretation classes: Very High>High>Medium>Low class. Results for the end of Phase I indicate that grain yield response to STP classes varies among sites and years.  Grain P removal was very responsive to the level of applied P or the target STP class.  At all locations, as the Interpretation Class went from Low to High or Very High, the amount of P removed in the grain also increased.