Minnesota Long-Term Phosphorus Management Trials.

Phosphorus fertilizer management in Minnesota is based on one of two philosophical approaches, Build and Maintain (B&M) and Sufficiency. Field research in the 1970s and 1980s suggested the Sufficiency approach applied less P fertilizer than the B&M approach while grain yields were similar indicating greater profitability with the Sufficiency approach. 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 as the Sufficiency approach will not maximize yield potential. These concerns led to the establishment of long-term field experiments that could be used to test phosphorus management strategies on soils with a defined long-term phosphorus history. The primary objective of Phase 1 (2010-2014, Build Period) of these experiments is to establish trials at six different locations across Minnesota with STP interpretation classes ranging from Low, Medium, High, and Very High. Initially at all sites, P fertilizer was applied at rates of 0, 30 , 60, and 90  lbs. P₂O₅ ac^-1 to whole plots with targeted STP interpretation categories of low, medium, high, and very high, respectively. In fall of each year, soil samples are taken from each split-plot to a depth of 6 inches to determine changes in STP levels. Two sites are having calcareous soils and are developing STP levels differently than other sites. Therefore, P fertilizer application rates are changed over years at few sites to achieve STP levels falling in the targeted STP interpretations categories. Crop biomass, P uptake and yield data are also taken from each plot to relate to STP levels or targeted STP interpretations categories.