Soil Phosphorus Dynamics Under Annual Vs. Single Applications of Alkaline Treated Biosolids.

The influence of annual alkaline-treated biosolids (ATB) land application on phosphorus (P) dynamics in soils needs to be better understood for more efficient P management. This four-year study explores the relationship between P accumulation and potential risks of losses, as well as changes in readily available P fractions in soils receiving different rates and application frequency of ATB. The application frequency treatments include annual ATB applications and a one-time ATB application. Application rates include control, 2 Mg ha^-1 lime, 7, 14, 28 and 42 Mg ATB  ha^-1. Treatments are arranged in a split plot factorial experiment with four replications. For the annual ATB applications, the highest Mehlich-3 (M3) extractable P and M3-P saturation index (PSI=[P_M3]/[Al_M3+Fe_M3]) was measured at 28 Mg ATB ha^-1 rate and was not significantly different with 42 Mg ATB ha^-1 rate. Year had no effect on M3-P concentrations and there was no treatment effects on water extractable P (WEP) under annual ATB treatments; however, lower WEP was measured in 2011 relative to the other years (p<0.05). For single biosolids application, similar responses for PSI, WEP and M3-P measures were observed relative to the annual ATB treatments. Total soil P and plant P uptake will be determined in the future for determine P accumulation and plant uptake P in soils.