Municipal Biosolids as an Alternative Nutrient Source for Bioenergy Crops: I. Elephantgrass Biomass Production and Soil Responses

High-yielding bioenergy crops remove large quantities of soil nutrients. Nutrients must be replenished in a manner that minimizes production costs and negative environmental impact. Class A municipal biosolids (MBS) were evaluated as an alternative nutrient source to inorganic fertilizer for 'Merkeron' and Chinese Cross elephantgrasses (Pennisetum purpureum Schum.) in a 2-yr field experiment in Florida. Elephantgrass plots received 0, 33, 67, or 100% of total N applied (350 kg ha(-1) yr(-1)) from MBS, with the remainder from NH4NO3. Dry matter (DM) yield, tissue N and P concentrations and removal, and soil C and P concentrations were assessed. Elephantgrass yield decreased linearly from 24.2 to 20.1 (Merkeron) and 24.3 to 16.9 Mg ha(-1) (Chinese Cross) as the percentage of N supplied by MBS increased from 0 to 100. Nitrogen removal decreased from 208 to 127 kg ha(-1) yr(-1) over the same range of N from MBS. Phosphorus removal ranged from 28 to 43 kg ha(-1) yr(-1), but the effect of N source was not consistent. There was no effect of percentage of N from MBS treatment on soil responses including water-extractable (WEP), Mehlich-1, or total P, nor was there an effect on total C concentration in the Ap horizon. Replacing 33% of N from inorganic fertilizer with N from MBS reduced elephantgrass biomass production 0 to 11%, so there is potential benefit to including MBS in a fertilization program for bioenergy crops, even in situations where MBS are limited to P-based application rates.