Management of grasslands by mowing versus grazing – impacts on soil organic matter quality and microbial functioning

Abstract

Although 30% of the European surface area is covered with grasslands, little is known about the effect of their management on soil quality and biogeochemical cycling. Here, we analysed soil from an experimental site in Western France, which had been under either grazing or mowing regime for 13 years. We aimed to assess the effect of the two management practices on the biogeochemical functioning of the soil system. To this end we compared soil organic matter (SOM) composition and microbial properties at two depths. We analysed for elemental, lignin and non-cellulosic polysaccharide content and composition, microbial biomass, soil microbial respiration and enzyme activities. Our results showed higher soil organic carbon (SOC) and nitrogen contents in the surface soil under grazing as compared to mowing. Soil biogeochemical properties also differed between grazing and mowing treatments. In particular, soil under grazing showed lower lignin and higher microbial biomass. Despite the similar non-cellulosic polysaccharide content under both treatments, microbial community under mowing was characterised by higher enzyme production per microbial biomass, leading to more degraded SOM in the mowing system as compared to grazing. We conclude that grazing and mowing regimes impact differently biogeochemical soil functioning. Higher and more diverse carbon input under grazing compared to mowing may lead to enhanced substrate availability and thus more efficient microbial functioning, which could favour SOC sequestration through formation of microbial products.