Tillage practices and their impact on soil organic carbon and the microbial community

Abstract: Soil microorganisms are important for climate regulation as well as for plant nutrition. In agricultural soils the microorganisms are affected by management choices, like which type of tillage that is used. Moldboard plowing, the most common tillage practice, increases mineralization which leads to soil organic carbon (SOC) loss, and may thus reduce soil quality. Conservation tillage practices infer less soil disturbance and they are considered to reduce mineralization compared to plowing, and favor fungi to greater extent than bacteria, which has been suggested to result in increased SOC content. Conservation tillage has been implemented by farmers worldwide to reduce soil erosion and also to improve farm economy. The main aims of this thesis were to find out how conservation tillage affect SOC concentrations and the soil microbial community compared to plowing, and which type of farmers that are likely to use conservation tillage and why. The effects of tillage practice on SOC, arbuscular mycorrhizal fungi (AMF), saprotrophic fungi and bacteria, were evaluated using three Swedish long-term tillage experiments, whereas a questionnaire was sent out to Scanian farmers to find out more about conservation tillage use. I found that long-term conservation tillage do not necessarily lead to an increase in SOC concentrations, and that fungi and particularly AMF benefit from reduced tillage. Although the tillage treatment effect on the microbial activity was not consistent, the respiration rate was often higher under conservation tillage than under plowing, at least when measured near the soil surface. Furthermore, a typical farmer who use conservation tillage is highly educated and work more than halftime with crop production. I also learned that crop rotation, labor savings and soil type are often considered when deciding on which tillage type to use. To conclude, use of conservation tillage may not increase SOC concentrations in the studied areas, but can still be attractive to farmers as it benefits AMF and can lead to better farm economy, if implemented on suitable soil and with an adapted crop rotation.