Bacterivorous nematodes correlate with soil fertility and improved crop production in an organic minimum tillage system

Organic farming systems are generally based on intensive soil tillage for seed bed preparation and weed control, which in the long-term often leads to reduced soil fertility. To avoid this, organic farming systems need to adopt conservation agriculture practices, such as minimum tillage and diligent crop rotations. However, minimum tillage generally delays soil warming in spring causing reduced nitrogen mineralization and thus poor plant growth. This negative effect needs to be compensated. We hypothesize that, in a diverse crop rotation, organic minimum tillage based on frequent cover cropping and application of dead mulch will improve soil fertility and thus crop production as confirmed by a number of chemical and biological soil indicators.We made use of two long-term field experiments that compare typical organic plough-based systems (25 cm) with minimum tillage systems (Results from the field experiments showed an increase of macronutrients (+52%), micronutrients (+11%), microbial biomass (+51%), microbial activity (+86%), and bacterivorous nematodes (+112%) in minimum tillage compared with the plough-based system. In the accompanying greenhouse bioassay, pea biomass was 45% higher under minimum than under plough tillage. In conclusion, the study showed that under organic conditions, soil fertility can be improved in minimum tillage systems by intensive cover cropping and application of dead mulch to levels higher than in a plough-based system. Furthermore, the abundance of bacterivorous nematodes can be used as a reliable indicator for the soil fertility status.