Field trial results of straw yield with different harvesting methods, and modelled effects on soil organic carbon. A case study from Southern Finland

We estimated the effects of different cutting heights and harvesting strategies on the amounts of harvestable residue biomasses and allocation of residue biomasses in the soil. A case study on regional straw biomass resources was performed with the different crops cultivated in Varsinais-Suomi (Southern Finland) at present (averages of 2003-2012) and in the predicted future warmer climate (scenario RCP 4.5, year 2055). We also estimated, with the help of the Yasso07 model, the effects of different residue incorporation intensities on soil organic carbon (SOC) at present and in the future warmer climate. The results suggested that cutting height has a significant impact on the amount of straw biomass incorporated in the soil and subsequent change in SOC. The impact depended on crop species and variety. When straw is collected and used e.g. in energy production, harvesting practices leaving greater stubble heights could help to maintain soil fertility. The Yasso07 model suggests that in the predicted future warmer conditions, more straw could be collected without decreasing SOC, as mineralization of SOC in the warmer climate is expected to increase less than organic carbon amendments caused by higher crop and root biomasses. Collection and usage of straw as a renewable energy source always decreases greenhouse gas (GHG) emissions in comparison to fossil fuels. However, collecting straw every second year instead of every year, even with higher stubble, would decrease field traffic and spare the soil from compaction and the farmer from extra work, while still significantly decreasing GHG emissions.