Corn Harvest and Nutrient Management Impacts On Phosphorus Loss with Surface Runoff.

Research is needed to investigate impacts of expanding bioenergy production systems on soil and water quality. Partial or total biomass removal in addition to grain harvest may change crop P needs, P will be removed that otherwise would be recycled into the soil, and both sediment and water loss may be altered. These changes could result in increased P loss from fields. Furthermore, interest in utilizing manure nutrients to minimize fertilizer use, necessitates research of potential differences for fertilizer or manure management systems. This 2-year study used plots with Clarion loam soil (mixed, superactive, typic Hapludolls) and a field rainfall simulation technique to study P loss from continuous corn (CC) harvested for above-ground biomass, grain, or grain plus a fraction of corn stover; corn-soybean rotation harvested for grain; and switchgrass harvested once per year for total biomass. Nutrient treatments were fertilizer or liquid-swine manure as N-P sources incorporated or injected to 174 m² plots each replicated three times. Simulated rainfall (76 mm hr^-1) was applied to 3 m² small plots until 30 min. of runoff occurred in the fall (after crop harvest) and in the spring after applying treatments and tillage but before planting the crops. The small plots were located in a different portion of large plots each season. We found inconsistent differences for runoff volume, sediment loss and concentration of dissolved reactive P, bioavailable P (estimated by the FeO-impregnated paper method), and total P in runoff among fertilizer or manure treatments and across fall or spring seasons. The largest average losses for all runoff P fractions were for CC managed with manure and total biomass harvest, while the smallest losses were for corn harvested for grain, soybean harvested for grain, and switchgrass harvested for total biomass.