Soil Phosphorus Accumulation Following 12 Years of Biosolids Application to Continuous Corn Cropping System in Central Minnesota.

Since 2003, a small, private wastewater treatment facility for St. John’s University located in Collegeville, MN has utilized a nearby agricultural field to routinely dispose of its Class B biosolids. The field soil textures range from sandy loam to loamy sand and have been managed under continuous corn (Zea mays L.) production since 2003. Repeated land applications of biosolids to this field has led to extractable phosphorus (P) (Bray-1) soil test values to accumulate beyond state-mandated levels for continued land application. The objective of this research was to quantify a general P budget in this cropping system based on previous management practices and to explore alternative cropping systems. Basic soil information was collected in 2015 and was combined with previous soil tests (including pH, salinity, organic matter %, Bray-I P, potassium, etc.) to quantify basic soil parameters and changes to soil P over time. Land management (crop yields, fertilizer source, and application rates, etc.) records were collected from the field manager and combined with biosolids chemistry data and application rates from the wastewater facility to construct a general P budget from 2003 to 2015. Using this information, we then explored alternative cropping scenarios to identify cropping systems which may sustain greater long-term soil health while maximizing annual P removal from the soil. This research will be used to guide future biosolids and field management decisions.