Frequent Drying-Wetting Cycles Following Freeze–Thaw in Manured Clayey Soil Increase CO2 Emissions

Abstract In cold climates, it is important to improve the health of clayey soils by incorporating organic matter. However, it is necessary to consider the environmental impact of this practice. This research investigates how CO 2 emissions from clayey soils with different organic matter content could be affected by modified drying-wetting cycles following freeze–thaw events, influenced by global warming. A trial with three replications was carried out under laboratory conditions with two different freeze–thaw cycles (FT1: 5 and FT2: 10 times) followed by three different drying and wetting cycles (DW1: 18 times every 3 days, DW2: 9 times every 6 days and DW3: 6 times every 9 days) in clayey soils with varying organic matter contents from cow manure (OM1: 2.47%, OM2: 3.30% and OM3: 5.46%). Frequent drying-wetting cycles with increasing manuring, CO2 emissions increased. Considering the main treatment effects, average CO 2 emissions increased by 26.9% and 75.8% in the OM3 treatment compared to OM2 and OM1 treatments, respectively, and by 23.7% and 44.5% in the DW1 treatment compared to DW2 and DW3 treatments, respectively. The highest average CO 2 emission was observed in the OM3-FT2-DW1 treatment (1.004 g m⁻ 2 h⁻ 1 ), which was 152.6% higher than the lowest value in the OM1-FT1-DW3 treatment. The soil exhibited significant ( p < 0.001) increases in electrical conductivity, available phosphorus (P 2 O 5 ), total Kjeldahl-N, wet aggregate stability, and porosity as organic matter content increased, while pH values decreased, resulting in higher CO 2 emissions. The study also found that CO 2 emissions increased significantly ( p < 0.001) with higher soil moisture and water evaporation (H 2 O emissions), but decreased with higher soil temperature. In conclusion, it was determined that the increased frequency of drying-wetting, when considering the significant decrease in CO 2 emissions in OM2 and OM1 treatments compared to OM3, suggests that the rates of organic matter added to the soil should be limited to levels that will ensure the maintenance of soil health and the environment.