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

Abstract

This study examined the effect of addition of byproducts generated from the biofuel industry on soil quality as measured by response of soil enzyme activity, microbial biomass C (MBC) and N (MBN) content and microbial quotient (MQ) to the addition of these materials over a short period of incubation. Byproducts of ethanol manufacture utilized included: wet distillers grain (WDG) and thin stillage (TS) that were applied at 3 rates of N (100, 200, and 400kgNha−1), whereas glycerol, a byproduct of biodiesel production, was applied at 3 rates of C (40, 400 and 4000kgCha−1) alone (G–N) or combined with 300kgNha−1 as urea (G+N). Urea and dehydrated alfalfa (DA) were applied at the same N rates as WDG and TS, as reference amendments. With the exception of TS and G–N, alkaline phosphatase activity was significantly enhanced by WDG, G+N, urea and DA addition, especially with low and medium rates. All amendments significantly increased dehydrogenase activity, but the rate effect was variable among all treatments. Protease activity was also enhanced by all amendment additions, with TS being less effective than others. All amendments with exception of TS significantly increased MBC, MBN and MQ. TS had no effect on these parameters, which is attributed to less organic carbon added relative to nitrogen in this amendment. Overall, addition of biofuel processing byproducts to soil stimulated microbial growth and enzyme activity; supporting their potential use as soil amendments to recycle plant nutrients and enhance soil biological activity.