Epsilon Archive for Student Projects

Abstract

Addressing the urgent need to adapt and mitigate climate change, a significant focus has been placed on reducing greenhouse gas emissions from agriculture. The cultivation of cover crops is an important agricultural practice, offering a multitude of benefits. These crops are meticulously selected based on the farmer’s goals, the main crops cultivated, soil conditions, and the local microclimate. In the Scandinavian context, oilseed radish (Raphanus Sativus L.), is a popular option, due to it fast growth, deep taproot and termination by frost. While environmental advantages have been well-documented, concurrent greenhouse gas measurements of oilseed radish and its residues have revealed a potential increase in emissions. Given the growing consensus on mitigating anthropogenic N2O emissions, further investigation into oilseed radish as a cover crop is warranted. Such research is imperative to weigh its benefits against its drawbacks and to derive strategies for effective mitigation measures. This thesis aim was to find out the relationships between N2O emission and different ages of frost-killed oilseed radish with a focus on the C:N ratios of the plant material. To address this objective, the hypothesis that the crop age of oilseed radish has an inverse relationship with N2O emissions was tested. Oilseed radish was cultivated in the greenhouse for the purposes of the incubation experiment. The cultivation period lasted 35 days. The three different ages of oilseed radish mentioned, refer to plant material harvested on three specific dates. Age 1 corresponds to plants grown for 21 days and harvested on the 21st day of the cultivation period. Age 2 represents plants grown for 28 days and harvested on the 28th day, while Age 3 indicates plants grown for 35 days and harvested on the 35th day. Subsamples of oilseed radish from each harvest were prepared and analysed for dry matter (DM) content, Total C and Total N. Additionaly, subsamples (6.7g) from each harvest, were randomly selected, packed in zip-lock plastic bags and put in the freezer for the incubation experiment. The soil used for both cultivation and incubation was obtained from soil sampling, air-dried, sieved, and crushed. Subsamples of the soil were taken for further analyses, including total C, total N, and pH measurement. The remaining soil was stored in a cold storage room for the incubation experiment. For soil packing in the incubation cylinders, soil water content was determined gravimetrically, and water was added to achieve 60% WFPS. The experimental setup involved four treatments: cylinders with only soil (control) and soil with oilseed radish frost-killed at three different ages (Age 1, Age 2, Age 3, and Csoil). Each treatment was replicated four times in a completely randomized design. Incubation occurred for 7 days in a dark cabinet at room temperature, followed by sampling and subsequent analyses to quantify N2O, CO2, and CH4 fluxes. Results showed that N2O emissions in the 3 different ages significantly differ from the control treatment. N2O fluxes per dry weight, showed that N2O emissions from oilseed radish frost-killed are notably higher in Age 1 and that can be related with the lowest C:N ratio (6) from the three treatments in the experiment and significantly high emissions. Interestingly, Age 2 didn’t appear to have higher emissions as expected. About carbon dioxide CO₂, emissions were higher in all of the treatments in comparison with the control. CO2 also used as an indicator of the activity of heterotrophs. CH₄ emissions showed no significant differences between treatments. It shows that frost-killed oilseed radish can enhance N2O emissions and other factors except from the C:N ratio should be explored for a better understanding of N2O in different ages of oilseed radish. This study indicates the intricate relationship between the age of frost-killed oilseed radish, its biochemical composition, and the surrounding environmental conditions. The unpredictability of these interactions necessitates further research to accurately determine greenhouse gas emissions from oilseed radish at various ages.