Biosolids processing effects on first- and second-year available nitrogen

Simple, reliable estimates of biosolids N availability are needed to develop land application programs that will benefit crops without risk of excess nitrate leaching. This study was conducted to assess the effect of biosolids processing on plant available nitrogen (PAN) release during the first and second growing seasons after application. We compared 14 sources of biosolids and a range of inorganic N rates in two replicated field experiments on established tall fescue (Festuca arundinacea Schreb.). The biosolids encompassed a range of treatment and dewatering/drying processes. A single biosolids application was made in May of the first year, and tall fescue yield and N uptake were measured by harvest for the next two growing seasons. Inorganic N was split across multiple applications each year. Fertilizer efficiency regression equations were developed for the inorganic N treatments, and used to calculate biosolids PAN from N uptake data. Year 1 PAN was similar across a range of biosolids treatment processes. For nonlagoon biosolids, PAN averaged 37 +/- 5% of total biosolids N. Lagoon biosolids PAN ranged from 8 to 25% of total N, with the oldest, most stable biosolids having the lowest PAN. Year 2 PAN averaged 13 +/- 2% for nonlagoon biosolids, excluding heat-dried materials, which were lower (5 to 8%). Our calculations indicated that about half of the Year 2 PAN became available during the cool season, suggesting that winter cover cropping may be needed to reduce the potential for nitrate leaching loss in summer annual cropping systems.