Phosphorous Loss In Tile Drains From Agricultural Lands, In Comparisons with Surface Runoff.

Phosphorus movement in sub-surface flow can be a significant pathway for soil P loss contributing to eutrophication of surface water resource. Studies were conducted in clay loam soils 1) to compare soil P losses in tile drainage with surface runoff water discharge; and 2) to evaluate the effects of major agricultural management practices on tile drainage P loss, including chemical fertilization, organic amendment, and tillage practices (no-tillage vs. conventional tillage). Soil water discharges, tile drainage and/or surface runoff, were monitored for flow volumes and sampled continuously year-round using auto-sampling systems. Water samples were analyzed for dissolved reactive P (DRP) and particular P (PP). Phosphorus loss in tile drainage accounted for 65-85% of total soil P loss, in which both DRP and PP played important roles. Either the level of soil test P or the flow volume of water discharge could be the driving force of soil P loss in tile drainage, depending on the specific conditions. Increased levels of soil test P with organic amendments increased soil P loss in tile drainage, regardless of tillage practices. The effects of organic amendment on soil P loss were further enhanced with non-tillage, relative to the conventional tillage. Beneficial management practices must be developed to minimize soil P loss in sub-surface flow.