Composition of the microbial community in long-term organic and conventional farming systems

Conventional agriculture has a remarkable influence on nature mainly due to the use of mineral fertilisers and chemical pesticides. Nowadays, organic farming is being increasingly transitioned towards regenerative agriculture. Long-term five-field crop rotation experiment investigated the effect of different fertilisation in organic and conventional farming systems. Soil chemical properties, microbial biomass, and microbial community structure in field trial with winter cover crops (OrgI) and winter cover crops with composted cattle manure (OrgII) as an organic farming system were analysed in comparison with conventional farming system with mineral fertilisers and chemical pesticides (ConvII) or only chemical pesticides without fertilisation (Conv0). Treatments with no extra organic amendments or mineral fertilisers were control for comparison. Two field experiments with different main crops were investigated: potato (pre-crop pea) and spring barley underseeded with red clover (pre-crop potato). All microbial groups (Gram-positive, Gram-negative, Actinobacteria, and fungi) were higher in organic farming systems (OrgII and OrgI) compared to conventional system in both treatments (potato and barley). The experiment with potato showed higher values of microbial biomass but little significant differences between fertilisation regardless of farming practice. The experiment with spring barley with red clover showed lower amount of microbial biomass, but biomass by microbial groups (Gram-positive and Gram-negative bacteria, total bacteria, Actinobacteria, and fungi) were significantly higher in treatments with organic amendments. The relative abundance of microbial community did not show significant differences between farming systems or fertilisation practices, except for higher abundance of Actinobacteria in conventional farming system indicating a significant effect of pesticides on this group. It was found that an organic farming system helps to maintain or increase the abundance of soil microbial community, which is an important part of soil health.