Differences in Phosphorus Availability Among Six Southeast Wisconsin Biosolids.

Maintaining a balance between controlling runoff/erosion losses of phosphorus (P) and providing adequate nutrients via soil amendments continues to be an important aspect of sustainable agricultural management.  Biosolids are beneficially reused by land application to provide nutrients and reduce landfill waste.  While research has shown that P availability from biosolids is different from that of manures, there has been little research to quantify the differences in P availability among different kinds of biosolids.  Agricultural producers using a P Index would benefit from knowing accurate P availability factors for specific biosolids.  The goal of this research is to quantify differences in phosphorus availability among six biosolids collected from wastewater treatment plants in southeastern Wisconsin.  An eleven week soil incubation was completed using a Plano silt loam soil incubated with six biosolids treatments (2 liquids, 4 solids), potassium phosphate, and a control (completed in quadruplicate).  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 time 0 (immediately after application) and at the end (week 11) for total P, Bray P1, water extractable P, P saturation, and total minerals.  These results should illuminate and quantify the anticipated differences between biosolids as related to phosphorus availability in soil.  Continuing the research with subsequent incubations using other agriculturally important soils in Wisconsin and more Wisconsin biosolids will help build a database that can be used to establish P availability factors for biosolids that can be used in the P Index.  This will allow agricultural producers to appropriately credit biosolids when land applied and supply adequate nutrients while protecting water quality.