Phosphorus Availability in Sand and Silt Loam Soils from Six Wisconsin Biosolids.

Tighter phosphorus regulations in Wisconsin will cause wastewater treatment plants to be required to remove even more phosphorus from wastewater.  The resulting biosolids will have increased phosphorus levels.  Understanding how different treatment processes affect phosphorus availability from biosolids is important for biosolids to be included in the Wisconsin Phosphorus Index.  The goal of this research is to quantify differences in phosphorus availability among six biosolids collected from wastewater treatment plants in southeastern Wisconsin.  Two eleven week soil incubations were completed using a Kewaunee silt loam and a Plainfield sand soil incubated with six biosolids treatments (2 liquids, 4 solids), potassium phosphate, and a control.  Soil amendments were applied at 40 kg P/ha and incubated at 60% water holding capacity and 25^oC.  Biosolids were characterized for pH, total solids, total nitrogen and phosphorus, as well as total minerals.  Soil was analyzed at the end of the incubation (week 11) for total P, Bray P1, water extractable P, P saturation, and total minerals.  These results should illuminate and quantify differences in phosphorus availability from biosolids applied to soil and provide P source factors necessary for biosolids to be included in the Wisconsin Phosphorus Index.  This will allow agricultural producers to appropriately credit biosolids when land applied and supply adequate nutrients while protecting water quality.