Agronomic Effectiveness and Environmental Risk of Phosphorus in Biosolids.

A field experiment was established in Fulton County, western Illinois to evaluate the P availability to plant and potential loss through runoff of biosolids relative to triple superphosphate (TSP). Lagoon-aged air-dried biosolids and TSP were incorporated into surface soil in fall 2005 at rates of 0, 163, 325, 488, 650 kg P ha^-1. Corn was planted once every year. We monitored the dynamics of Olsen extractable P in surface (0 - 15 cm) soil for three consecutive years. We collected bulk soil samples from each treatment and conducted simulated runoff studies to determine the potential P loss through runoff. Both Olsen-P in soil and Molybdate-reactive P (MRP) in runoff showed contrasting responses to the P addition for biosolids and TSP. During the first two years of the experiment, the responses of soil Olsen-P and runoff MRP to TSP fertilization were two times greater than those to biosolids-P. The soil Olsen-P and runoff MRP from TSP treatment decreased with time faster than those from biosolids treatment. But, the soil Olsen-P and runoff MRP still responded more to TSP fertilization than biosolids-P in the third year, though the differences in such responses between the two P sources decreased. The study therefore supports our hypothesis that biosolids P could be applied at a rate greater than recommended for commercial P fertilizer. The use of biosolids apparently avoids the “short term” spikes of P release associated with commercial P fertilizers, while still providing adequate plant-available P.