Seasonal patterns of N2O and CO2 emissions from Finnish agricultural soil under oat with and without cover crops as affected by reduced rainfall

Nordic agricultural production faces multiple challenges in a warming climate. Although predictions indicate an overall increase in annual mean precipitation in northern Europe, increasing temperatures may lead to earlier snowmelt and drying of soil during springtime, as well as longer growing season and higher evapotranspiration increasing the risk of summer droughts. The use of cover crops in agriculture is one of the climate-smart practices that have multiple benefits, such as increasing SOC, reducing N losses, and increasing biodiversity. Still, the question whether cover crops and their diversity increase resilience against climate extremes such as drought, and how the combined effects of cover crops, their diversity and drought affect greenhouse gas (GHG) emissions from soil remain largely unknown. We studied the effect of cover crop diversity and drought on soil and crop C and N dynamics and GHG (CO₂, N₂O) emissions in a biodiversity cropland experiment with or without shelters that remove 50% of incoming precipitation for two years. GHG emissions were measured with the manual dark chamber method twice a week during growing season and once a week during off-season. Soil temperature and water content were measured continuously, and the soil was sampled for mineral N and total C and N analysis seasonally.

The preliminary results showed that reduced rainfall did not affect N₂O emissions significantly during the growing season in either year. During off-season, reduced rainfall led to elevated N₂O emissions irrespective of cover crop diversity treatments. However, the effect was absent in the second year, indicating that factors other than drought were driving the N₂O production. Contrary to N₂O, drought did not affect CO₂ emissions during off-season in either year. Overall, during both years off-season N₂O emissions dominated the annual N₂O balance in all diversity treatments, highlighting the importance of including off-season measurements to the annual N₂O balance estimation.