Biochar amendments make the harvesting of crop residue for bioenergy production sustainable

The Pyrolysis-Biochar-Bioenergy Platform (PBBP) has the potential to be developed into a new economically-viable industry that helps mitigate climate change. However, the harvesting of crop residues for bioenergy production inherently removes plant nutrients from soils and expropriates organic residues that are needed to build new soil organic matter. Here we consider whether the biochar co-product of PBBP is effective for making the harvesting of crop residues sustainable. A Minnesota agricultural field lost 7 Mg of C per hectare as a legacy of 19 years of crop residue harvesting. Residue harvesting also adversely impacted other measured soil quality parameters. Data compiled from nine studies, indicate that biochar amendments improved numerous soil quality parameters, including soil organic C, total N, bulk density, pH, CEC, aggregation, porosity, soil water retention, available K, and available P. The analysis indicates that 6 to 11 Mg of biochar C could be produced from maize residue harvested from one hectare of land for 19 years, which is enough to fully compensate for the loss of SOC and the degradation of soil quality on the Minnesota field. However, biochars need to be prepared at peak pyrolysis temperatures of 500 & DEG;C or higher to be stable and biochar amendments need to be combined with other soil conservation practices to allow sustainable harvesting of crop residues for the production bioenergy.