Management of Municipal Biosolids Affects Organic Nitrogen Mineralization and Elephantgrass Yield.

Adequate nutrient supply is necessary for high-yielding bioenergy crops, but minimizing production cost is critical. Municipal biosolids (MBS) represent an alternative source of nutrients to commercial fertilizers, thus understanding the effect of management practices on MBS nutrient release patterns is important. This study evaluated the effect of season of application and incorporation of MBS on organic N mineralization. Polyester litter bags containing 25 g of MBS were incubated in the field during the 2007 and 2008 elephantgrass (Pennisetum purpureum Shum.) growing period. Treatments were season when MBS were placed in the field (summer vs. spring) and incorporation (5-cm depth vs. surfaced-applied). The effect of incorporation on dry matter (DM) yield of elephantgrass was also evaluated in a separate experiment in the same area. Total organic N mineralized was 347 and 428 g kg^-1 in 2007 and 2008, respectively. Average daily organic N mineralization rates during the first 48-d period after incubation were greater for summer compared to spring application, with values of 7.3 and 4.6 g kg^-1 d^-1 in 2007 and 6.7 and 4.7 g kg^-1 d^-1, respectively, in 2008. Incorporation of MBS resulted in an additional 70 g organic N mineralized kg^-1 of organic N than for surface-applied MBS (22% increase). Further, when MBS were incorporated, elephantgrass DM yield was not different than when N was supplied by ammonium nitrate fertilizer, and DM yields in both treatments were greater than when MBS were surface-applied. Results suggest that MBS is a viable alternative to commercial fertilizers and that incorporation of MBS should be encouraged in order to maximize crop yield while minimizing nutrient losses.