Saponins in soil, their degradation and effect on soil enzymatic activities

Saponins can be potential candidates for the development of safe biopesticides, due to their widely acknowledged insecticidal, fungicidal and nematicidal activity, but information on their effects on soil biological properties is still limited. This study aimed to investigate the short-term fate of saponins from Medicago sativa in soil and their dose-effect relationship with microbial biomass and selected enzyme activities in soils with different origin, physical and chemical properties. Microbial degradation of total saponins ranged from 46 % to 91 %, according to soil characteristics, within 28 days from their incorporation into the soil. Both saponin glycosidic chains and triterpenic aglycones were also microbially degraded, though by dynamics changing among the different soils. In all soils, M. sativa saponins significantly reduced microbial biomass at rates of 10 and 20 mg saponin mixture per g of soil. Microbial enzymatic activities were less affected as indicating an adaptive response of soil microbial communities to the presence of saponins.