If Sand Interlayer Acts Better than Straw Interlayer for Saline Soil Amelioration? A Three-Year Field Experiment

An addition of straw interlayer in the 0.40 m soil depth could effectively reduce salt accumulation in the surface soils by regulating water fluxes, thus mitigating the salt stress to the crop growth and development. However, the positive effects of straw interlayer were weakened with straw decomposition, and whether we could use sand (an indecomposable substance) instead of straw for saline soil amelioration still needs further investigation. Therefore, a three-year field experiment was established with straw and sand interlayers, as well as with no interlayer as a control. Straw interlayer demonstrated an increase of 4.85~13.10% of water content, while the sand interlayer increased 12.41~16.48% of water content in the soil layer of 0–0.40 m depth comparing to the control. Salt contents were lowered by 10.69~17.01% in the same soil layer of the straw interlayer and lowered by 7.00~7.59% in the sand interlayer treatment after irrigation. Data also shows that irrigation significantly increased water content and lowered salt accumulation in the soil plough layer, thus increasing the sunflower emergence rate of 10.49~13.54% in the straw interlayer treatment and 12.53~14.78% in the sand interlayer treatment, respectively. Both the straw interlayer and sand interlayer treatments effectively reduced the evaporation of groundwater and established a beneficial plough layer with a lower salt accumulation throughout the sunflower growth period. At harvesting stage, the evaporation fluxes of salt in the straw interlayer and sand interlayer treatments were significantly lower than that in the control treatment. Lower salt accumulation conferred a beneficial promotion for the growth of sunflower, while the grain yields in the straw interlayer treatment were increased by 8.67% in 2018, 11.00% in 2019 and 17.37% in 2020 compared to the no-interlayer soil, respectively. However, the low water content in the soil layer of 0–0.40 m depth in the sand interlayer treatment inhibited the growth of sunflower, resulting in a significant decrease in the seed yields. It is worth noting that the precipitation effectively alleviated water stress on the sunflower at the middle and late growth stage in the sand interlayer treatment. This study suggests that a maize straw burial of 0.05 m thickness at a depth of 0.40 m soil layer could be used as an effective tillage practice that could improve the distribution of water and salt in saline soils.