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Biosolids Amendment and Harvest Frequency Affect Nitrogen Use Dynamics of Switchgrass Grown for Biofuel Production

Biosolids Amendment and Harvest Frequency Affect Nitrogen Use Dynamics of Switchgrass Grown for Biofuel Production

Nitrogen use efficiency (NUE) is a crucial index for developing sustainable bioenergy cropping systems. The objective of this study was to examine switchgrass (Panicum virgatum L.) NUE by using a low-cost organic amendment under different harvest frequencies. Aerobically digested biosolids were applied at 0, 153, 306, and 459 kg N ha−1 in a small plot study, and lime-stabilized biosolids were applied at 0, 77, and 154 kg N ha−1 in a field-scale study in Virginia, USA. Switchgrass was harvested once or twice per season. Switchgrass N concentration and N removal were measured to estimate switchgrass NUE, annual N recovery (ANR), and partial factor productivity (PFP). Across N rates, biosolid application increased biomass N concentration and removal by 29 % and 84 % and decreased NUE, ANR, and PFP in the plot study, but effects were inconsistent in the field study. Low NUE, ANR, and PFP obtained with a single, end-of-season harvest were likely functions of low feedstock N concentrations. Switchgrass harvested in summer had highest N concentrations. Cutting twice per season removed more N than cutting once; the resulting increase in NUE reflects differences in feedstock N concentrations rather than differences in yield. Our results suggest that biosolids can be applied as an alternative N source to support plant growth, and cutting once per season is preferable in sustainable biofuel production systems.

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