CO2 Flux from Farmland across Salinization Gradients during 1 Freeze–Thaw Periods under Winter Irrigation

Fan Luo¹Xinghong He¹Yiwei Chen¹Rui Gao¹Yuan Ma¹Shiyuan Liu¹Yao Guan¹Yuying Ma^2*

• ¹Tarim University, Aral, China
• ²Tianjin Agricultural University, Tianjin, China

Winter irrigation, as an effective agricultural practice, exerts positive effects on spring-sown 9 crops and is widely applied in Xinjiang, China. Under the influence of seasonal freeze–thaw cycles, 10 the mechanisms by which winter irrigation affects farmland carbon emissions are of great 11 significance for both agricultural production and greenhouse gas emissions. Therefore, conducting 12 relevant research is extremely necessary. A field plot experiment was conducted with three salinity 13 gradient levels. The flood irrigation and drip irrigation were applied during the non-growing period 14 following cotton harvest, with three irrigation amounts. The results indicated that as the soil froze 15 and thawed, CO2 emissions exhibited a trend of initially decreasing and then increasing. During the 16 pre-freezing period, winter irrigation intensified salt accumulation in the unfrozen zones, thereby 17 restricting gas emissions. The rate of decline in CO2 fluxes increased with irrigation amount, and 18 this effect became more pronounced as soil salinity increased. In the high-and medium-salinity 19 treatments, irrigation significantly reduced CO2 emissions, with the emissions under the irrigation 20 treatments being approximately half of those observed in the control treatment. However, during 21 the thawing period, the redistribution of soil salt and moisture weakened the effect of irrigation and 22 irrigation no longer had no significant effect on CO2 emissions. The soil salinity became the only 23 influential factor. Moreover, since CO2 emissions during the thawing period were much higher than 24 those during the pre-freezing period, the overall effect of winter irrigation on CO2 emissions across 25 the entire freeze–thaw cycle was not significant. From the perspective of carbon sequestration and 26 emission reduction, winter irrigation is a neutral agricultural practice, neither reducing carbon 27 emissions nor increasing the risk of carbon release.