Enzymatic activity and microbial biomass in soil amended with biofuel processing byproducts

Abstract

Plant essential nutrient and carbon contained in byproducts associated with biofuel production have increased their value as soil organic amendments. These byproducts include wet distillers grain, and thin stillage from ethanol production, and glycerol from biodiesel production. However, the potential of using these organic materials as soil amendment has not received enough attention yet. As a consequence, this study aimed to assess the impact of wet distillers grain, thin stillage and glycerol applied at three rates equivalent to 100, 200 or 400 kg N ha-1 in case of WDG and TS or 40, 400 or 4000 kg C ha-1 applied alone or combined with 300 kg N ha- 1 as urea in case of glycerol on enzymes activity of alkaline phosphatase, protease and dehydrogenase, and microbial biomass C and N content. Urea and dehydrated alfalfa were also applied at three rates of N for comparison as conventional amendments and reference materials. Amended soil was incubated in controlled growth chambers for 10 days. Addition of urea, DA, WDG and GL+N significantly enhanced phosphatase activity especially at the low rate. Protease activity was significantly enhanced by all amendments addition especially glycerol. All amendments increased dehydrogenase activity, especially TS treatments. With the exception of TS, all amendments showed variable effect but significant on MBC and MBN content. The significant impact of BPB on measured microbial parameters is probably as a consequence of their effect on microbial growth and activity.