4.3 Responses of SOC and TN to moisture and salinity in saline soil
The previous studies have showed that the straw interlayer can effectively increase water content, reduce salinity, and significantly increase crop yield (Zhao et al., 2016; Zhang et al., 2020). Furthermore, we found that SOC and TN contents were positively correlated with soil moisture and negatively with salt during 2015-2017 (p <0.01). In this study, the experimental plots were irrigated before planting sunflowers, and the straw interlayers could have extended the residential time of water in the upper part of straw interlayer and increased the water content in soil. Meanwhile, salt leaching was promoted to reduce the soil salt in root distribution layer (Zhao et al., 2016; Zhang et al., 2020). Additionally, the high-moisture and low-salt environment may be more conducive to the survival of soil microorganisms, thereby transforming the straw interlayer and increasing the SOC and TN contents (Li et al., 2017).
The SOC and TN contents had significantly negative correlation with soil salinity only in 2018 (p <0.01). With the increase of the straw interlayer burial period, the depth of the interlayer became thinner, and the regulation of water and salt weakened (Zhang et al., 2020). However, the salt content in 0-40 cm layer remained at a moderately level within the fourth year of straw interlayer burial. It may be beneficial to crop growth and residues induced-C transformation. Furthermore, the correlation analysis also confirmed that sunflower yield had a significant positive correlation with SOC and TN. Overall, straw interlayer with a single dose of 12 Mg ha-1 was recommended for improving SOC and TN during the first three years, it was beneficial for lowing soil salinity, while benefiting soil water content and crop yield in saline soil.