Microbial and enzyme analysis of soil after the agricultural utilization of biogas digestate and mineral mining waste

Abstract

The intensity of organic matter transformation in soil may be subject to various factors, especially to the previously applied non-standard chemical-based fertilizers. The objective of study was to assess the number of selected groups of microorganisms and enzymatic activity in soil after waste utilization. Biogas digestate (1.5 and 3.0%) and mineral mining waste (10 and 20%) were added to podzolic soil. The results demonstrated that the application of these wastes increased the number of microorganisms in the soil. 20% mineral mining waste provided the most favorable conditions for the development of oligotrophs and copiotrophs, whereas 3% biogas digestate most positively affected the total number of bacteria. This waste increased soil enzyme activity proportionally to the applied concentration. The highest activity was obtained for 1.5% biogas digestate. The number of oligotrophs, copiotrophs, and proteolytic microorganisms correlated positively with pH, organic carbon content, total nitrogen, and micronutrients present in the soil, while negatively with phosphorus content. The activity of the majority of enzymes was positively correlated with the content of mineral nitrogen, phosphorus, and potassium. In this study, we were not able to demonstrate a negative correlation between the content of heavy metals and the number of microorganisms in the soil. These results suggest that biogas digestate and mineral mining waste can be used in agricultural practice to improve microbial activity of the subsoil with a large reserve of safety for the soil environment.