Long-Term Patterns of Soil Test Phosphorus and Phosphorus Loss in Soils Historically Applied with Swine Manure Compost.

Soils continuously receiving organic amendments often result in excessively elevated levels of phosphorus (P), which may cause failure of surface water quality through P losses in soil erosion and surface and sub-surface runoff. Immediate and significant questions remain on fate of soil test P, agronomic sustainability and environmental value of P draw-down, once the high P soils are in process of remediation. A field experiment was conducted to assess the effects of legacy P resulted from historical pig manure compost additions on crop yields and soil test P change under a corn-soybean rotation in a Brookston clay loam soil of the Lake Erie basin in a 9-year period from 2008 to 2016. Water quality effects of soil P losses in both surface runoff and tile drainage were monitored continuously year-round using a state-of-the-art auto-sampling system. Both yields of corn and soybean with legacy P were highly identical to those with continuous P addition. Soil test P with legacy P declined linearly with time at 2.3 mg P kg^-1 year^-1, while with continuous P addition it remained unchanged. Relative to continuous P addition, crop use of legacy P significantly decreased dissolved P and particular P, eventually the total P loss by 36%. Meanwhile, crop production income increased by 15%. The results demonstrate that utilization of legacy P in soils can be an effective practice that enables farmers to improve production profitability, while restoring the ecosystems and health of surface water in lakes and rivers.