To plow a lot, a little or not at all
For farmers who focus on crop production, tillage, such as plowing, has long been a fundamental part of agriculture. The plow is an effective tool that incorporates weeds to reduce interference with the new crop. During plowing the soil microorganisms are also brought into contact with new food resources. When the microorganisms decompose organic matter, nutrients that promote crop growth are released. At the same time microbial respiration increases and soil carbon is released in the form of carbon dioxide. In the long run, plowing can cause soil to become less fertile, as the return of soil organic carbon does not outweigh the amount of carbon that is respired.
To reduce the negative impact of plowing, some farmers have begun to use different reduced tillage methods. Some farmers have even stopped doing any tillage before sowing. These new methods mean that the soil is less disturbed and the amount of plant residues left on the surface increases, which protects the soil against erosion. Farmers who use these milder forms of soil cultivation also save both time and money, as fewer hours and less fuel is required. Reduced tillage could also potentially benefit soil carbon sequestration, thus reducing the negative climate impact of agriculture.
Sofia Hydbom has studied how different combinations of plowing and harrowing affect the soil's microorganisms and its carbon content. The results show that the amount of symbiotic fungi increases with reduced tillage, and there is also evidence that the amount of saprotrophic fungi increases. However, her studies could not show that reduced tillage is an adequate measure to increase the soil's carbon content.
- I found that the respiration rate in the upper soil layers was often higher when not plowing. This is probably due to the higher amount of crop residues at this depth, compared to in plowed soil where the residues are buried deeper, says Sofia Hydbom.
Sofia has also studied how farmers in Skåne relate to reduced tillage. Sofia's survey shows that the choice of tillage method is determined by factors such as crop rotation, time, crop yield and the soil texture.
- Saving time and money are common arguments for transition to reduced tillage, but some of the farmers in Skåne point out that reduced tillage sometimes lead to an increased use of pesticides, says Sofia Hydbom.
Sofia Hydbom defends her thesis Tillage practices and their impact on soil organic carbon and the microbial community on Friday, December 8th.