Where other factors are not limiting, biosolids are land applied at “agronomic rates” to ensure that surplus nitrogen (above crop requirements) will be minimized. This measure is intended to reduce nitrate leaching and provide groundwater protection. There is no universally accepted method for predicting nitrogen (N) availability and determining the agronomic rate. Recent studies indicate that N mineralization rates and subsequent N availability from biosolids may be higher than historic guidance levels. To evaluate this issue a Water Environment Research Foundation (WERF) study was conceived and is being implemented. The study will evaluate three approaches to predicting N availability: present decay series (mineralization rate) guidance, a field incubation method, and a seven day laboratory incubation method combined with simulation modeling. Each will be compared to actual nitrogen availability estimates based on crop N uptake in field experiments. Field studies will be conducted in a cooperative effort involving the University of Arkansas, Michigan State, Oregon State, Washington State, University of Washington, and Alcorn State University. Biosolids derived from a variety of common processes will be used in the study. By evaluating biosolids with different characteristics and experimenting at locations covering a range of climatic and soil conditions, recommendations for standard practices applicable across the country can be developed.