Soil Phosphorus Accumulation Following 20 Years of Wheat-Fallow with Biosolids.

Beginning in 1993, biosolids have been applied every other year to a wheat-fallow field north east Colorado.  The biosolids were applied at five different rates, but for this study we focused on the control, 4.5 Mg/ha (agronomic rate), and 11 Mg/ha.  Soil samples were collected down to 120 cm, following wheat harvest in 2013, in zero contamination tubes.  The samples were then separated into 5-10 cm depth increments in the lab prior to analysis.  The samples were then analyzed for CaCO₃ and total P.  The soil P was also fractionated into three inorganic pools and five organic pools.  The results of the study will be presented.