Phosphorus Buffering Capacity, Water Extractable P, and Total P in Biosolids Treated Soils.
Angela Ebeling1, Larry Bundy1, Daniel Ebeling2, and Faith Blum2. (1) Univ of Wisconsin, 1525 Observatory Dr, Madison, WI 53706, (2) Wisconsin Lutheran College, 8800 W Bluemound Rd, Milwaukee, WI 53226
Biosolids are a product of waste water treatment processes. These processes may affect plant availability and water solubility of phosphorus (P) from the resulting biosolids when they are land-applied. The objectives of this research were to (a) determine changes in soil test P following biosolids P additions (phosphorus buffering capacity - PBC), (b) compare total P and water extractable P as predictors of soil test P change following biosolids P additions, and (c) incorporate PBC values and water solubility values for biosolids into the Wisconsin phosphorus index. An incubation was conducted using five silt loam soils with varying biosolids application histories in a completely randomized design with six P sources (four biosolids with lime, iron (Fe), aluminum (Al), and biological treatments, dairy manure, and an inorganic P fertilizer) applied at 110 kg P ha-1. After incubating for 16 weeks at 25oC and 60% water holding capacity samples were analyzed for pH, Bray P1 (BP1), water extractable P (WEP), phosphorus buffering capacity, and ammonium oxalate extractable P, Fe, and Al for calculating P saturation. Biosolids amended with Fe and Al changed BP1 the least while the lime amended biosolids decreased WEP compared to the control. Also a history of biosolids additions tended to increase soil PBC. The PBC is dramatically affected if water extractable P of the P source is used to calculate the P rate instead of total P. All P source treatments increased the P saturation compared to the control and there was a trend for higher P saturation with increasing biosolids history.