Phosphorus loss with surface runoff as affected by bioenergy-based residue and nutrient management systems for an Iowa loam soil

Growing interest in biofuel generation with cellulosic biomass from row crop residues necessitates research to investigate biomass and nutrient management systems impacts water quality. The objective of this research was to evaluate the impact of a range of cropping and corn biomass harvest systems on P loss with surface runoff as affected by N--P management based on inorganic fertilizers or liquid swine manure. A 2--year rainfall simulation study was conducted on established field plots with Clarion loam soil (mixed, superactive, Typic Hapludolls). Eight treatments, each replicated three times, were set up in a completely randomized block design using 174 m2 plots. Treatments consisted of continuous corn (CC) harvested for total above--ground biomass or grain managed with N--P fertilizer or N--based liquid swine manure for corn (four); CC harvested for grain plus a fraction of cornstalks managed with N--P fertilizer (one); corn--soybean rotation harvested for grain managed with N--based manure for corn (one treatment, but each crop phase was planted each year); and switchgrass managed with N--P fertilizer or in plots with a long history of manure application (two) harvested once per year for total biomass. The P fertilizer was applied at rates necessary to maintain recommended optimal soil--test P for crop growth. Simulated--rainfall (76 mm hr-1) was applied to 3 m2 microplots, located in different parts of each large plot each year until 30 min of runoff occurred in the fall and in the spring of each year. Residue cover, total runoff, sediment loss, and concentrations of dissolved reactive P, bioavailable P (estimated by the FeO--impregnated paper method), and total P in runoff were measured. The largest losses of all runoff P fractions were for CC managed with N--based manure and total biomass harvest, which showed the highest soil P concentrations among the grain crops. Differences among all other treatments were small and inconsistent in the fall season, but in spring the two switchgrass treatments showed the lowest loss of bioavailable and total P.