Effects of Biosolids Application and Harvest Management On Soil Carbon and Nitrogen in Biofuel Production Systems.

Management has large potential impact on biofuel system sustainability.  Biosolids application rates and harvest frequency effects on soil carbon (C) and nitrogen (N) under switchgrass (Panicum virgatum L.) were investigated. Anaerobically digested, pasteurized and dewatered biosolids were applied once to a long-term switchgrass stand at rates of 0, 153, 306, and 459 kg N ha^-1in a plot study at Orange, VA. Soil was sampled to 5 cm depth before treatment application and after two growing seasons to determine treatment effects on soil bulk density, and C and N concentration and mass.

Biosolids application increased (P<0.05) soil C and N by 6.2 and 0.5 g kg^-1 over the control, but differences among biosolids treatments were not detected (mean = 37.7 and 3.0 g kg^-1). Biosolids increased (P<0.05) soil C and N stocks by 4.4 and 0.3 Mg/ha over control (15.4 and 1.3 Mg ha^-1), although no differences among biosolids rates were observed (mean =19.8 and 1.6 Mg ha^-1). Soil C and N concentrations were greater under in one-cut management, but no differences of mass C and N were observed. Biosolids application did not affect soil bulk density, but harvesting twice per season increased (p=0.027) soil bulk density over that of the one-cut system (1.2 vs. 1.1 g cm^-3).  Sustainability metrics in biofuel systems are affected by harvest management and fertility inputs. Biosolids can serve as an alternative N source and can increase soil C and N, and thus have potential to improve biofuel production system sustainability.