Effects of long-term application of Vinasse on physicochemical properties, heavy metals content and microbial diversity in sugarcane field soil

Vinasse is the waste liquid of molasses fermentation for alcohol production from sugarcane mills. The adequate utilization and treatment for vinasse have received increasing attention. Among the alternatives considered for the reuse of vinasse, irrigation in sugarcane fields is most common solution. However, few researchers consider the impact on the soil fertility, soil heavy metals content and soil microbial diversity by long-term application of vinasse in the fields. In order to evaluate the cumulative impact arising from the long-term application of vinasse, different treatments, viz., (1) soils not irrigated with vinasse, (2) soil irrigated with vinasse for 2 years, (3) soil irrigated with vinasse for 7 years, (4) soil irrigated with vinasse for 13 years, (5) soil irrigated with vinasse for 18 years, have been applied to sugarcane fields in Shangsi County, Guangxi, China. The pH, organic matter, total and available N, P, K, the concentration of Cu, Pb, Cr, Zn, Ni, Cd and As, as well as the diversity of microbial community of the soil samples were determined. The results showed that after long-term irrigation by vinasse, soil acidification was observed, organic matter, N and K content increased, but no significant changes in the increase in P content were observed. The potential ecological risk of Cd, Cr, Pb, Zn, Cu, Ni and As was low, indicating that accumulation of heavy metals in the soil was negligible when long-term irrigation with vinasse was practiced. The diversity of microbial community expressed as relative abundance of the predominant species in irrigated soil was slightly reduced due to influence by the physicochemical properties of soil, especially soil pH. Consequently, the proper management of vinasse irrigation and periodic monitoring of soil quality parameters are required to ensure safe and long-term irrigation