Influence of Contrasting Biochar Types on Five Soils at Increasing Rates of Application

A series of experiments was established to characterize biochars made from four feedstocks regionally available in the Pacific Northwest (wood pellets, soft wood bark, switchgrass (Panicum virgatum L.) straw, and anaerobically digested fiber) to determine their effect on five soils. Soils were amended with 9.8, 19.5, and 39.0 Mg ha(-1) of each of the four biochars and evaluated for changes in pH, water holding capacity, N mineralization, and soil C. The C content of biochars derived from the herbaceous feedstocks was 60 to 67 kg kg(-1) whereas that of the woody feedstocks was > 75 kg kg(-1). In amended soils we found that biochars, regardless of origin, significantly raised the pH of all soil types 0.1 to 0.9 units, with the greatest impact on a sand soil. The biochars increased the soil C and water holding capacity at the higher rates of amendment depending on soil and biochar type. Nitrogen mineralization rates decreased in three of the five soils across all feedstocks. There were significant correlations (r >= 0.9) between biochar C measured and biochar C added regardless of feedstock or soil type. Our research demonstrates that in temperate soils, biochar feedstock may not be as important a variable as soil type for increasing C content and pH but can influence N mineralization and water holding capacity.