Incorporation of Municipal Biosolids Affects Organic Nitrogen Mineralization and Elephantgrass Biomass Production

Municipal biosolids (MBS) represents an alternative source of nutrients for the production of bioenergy crops like elephantgrass (Pennisetum purpureum Schum.). Two experiments were conducted during 2 yr in Florida to evaluate the effect of soil incorporation vs. surface application of MBS on: (i) elephantgrass dry matter (DM) yield, tissue N and P concentration and removal, and soil C and P (Exp. 1); and (ii) organic N mineralization and DM decomposition rates of MBS measured in the field using a litter bag incubation technique (Exp. 2). In Exp. 1, three treatments supplied 350 kg total N ha(-1) yr(-1) from surface-applied municipal biosolids (MBS-SA), soil-incorporated municipal biosolids (MBS-INC), and surface-applied ammonium nitrate (NH4NO3). A fourth treatment provided 700 kg total N ha(-1) yr(-1) from MBS-SA (double rate of municipal biosolids, 2x-MBS). In Exp. 2, MBS was field incubated in litter bags placed on the soil surface or at a 5-cm soil depth. Elephantgrass DM yield, and N and P removal were greater for MBS-INC than MBS-SA. Dry matter yield for MBS-INC was not different than for NH4NO3 fertilizer (22.5 vs. 24.3 Mg ha(-1)). Removal of N and P increased 39 and 10 kg ha(-1) yr(-1), respectively, for MBS-INC and MBS-SA. Total organic N mineralized was greater for MBS-INC (386 g kg(-1)) than MBS-SA (308 g kg(-1)). Incorporation of MBS increases elephantgrass DM yield and nutrient removal compared to surface application and allows MBS to replace a greater proportion of inorganic N fertilizer.