An experimental test of the effect of management strategies and rotation on plant-pathogen suppression by soil microbial communities

Soil is a highly complex habitat, with an exceptional diversity of microbial life. Interactions within the microbial community can be manipulated by rotation, tillage and organic amendment. However, the responses are not yet predictable, as the mechanisms linking these to soil suppression are not fully understood. The objective of the current research is to investigate and design management strategies to promote microbial mediated soil suppressiveness toward soil-borne pathogens and measure changes in soil biota due to these management strategies. A wide range of soil biota as well as disease suppressive properties of the soil were assessed in a field trial with a winter wheat based rotation. The objective was to detect shifts in the communities of different soil biota due to cultural and management strategies. Such information could facilitate the design of management strategies to promote microbe-mediated soil suppressiveness toward soil-borne pathogens. Two management systems were compared: (1) a control system including ploughing before sowing which is the currently applied system in the region, and (2) an innovative system targeting a better energy ratio, less greenhouse gas emissions, time saving for farmers and reduction of inputs especially nitrogen fertilization and pesticide applications. Both crop rotations consisted of winter wheat, winter oilseed rape, sugar beet and faba bean, but the innovative system had an additional crop linseed and cover crops between the main crops. Soil management strategies and crop rotation influenced the communities of bacteria, fungi including arbuscular mycorrhizal fungi, and nematodes in soil. Community shifts could be either due to the preceding crop, or due to the management system. Soil suppressiveness differed for 1 out of 3 soil-borne pathogens tested. However, in general the natural soil in the assessed field was quite suppressive against the diseases, and several antagonistic bacteria (Pseudomonas and Lysobacter) were isolated from the soil samples. The results showed the influence of management practices on soil biota and soil suppressiveness, indicating the potential of ecological engineering approaches to IPM through habitat manipulation at the field. However, distinct advises on management practices in relation to IPM will depend on the pathogens present in the field and the environmental conditions such as soil type, crop rotation and management. Extensive research is needed to get sufficient knowledge on the relevant soil processes before practical implementation is possible.