5. CONCLUSIONS
A 4-year field experiment demonstrated that straw interlayers (40 cm
soil depth) increased SOC content by 16-24% compared to no straw
interlayer (CK), ranged widely according to the straw input. Compared
with CK, the increase of SOC content was decreased for straw interlayers
with 6 and 12 Mg ha-1, while it was increased for 18
Mg ha-1 with the experimental years. The SOC content
of straw interlayer with 12 Mg
ha-1 was highest in 2015-2017, while it was highest
with 18 Mg ha-1 in 2018. The TN contents of straw
interlayers were increased by 9-13% compared to CK, while the increment
was lower than SOC content. Remarkable increases were obtained in the
soil layers above (20-40 cm) and below (40-60 cm) the straw interlayers.
Therefore, the C:N ratios of straw interlayers increased in 20-60 cm
layers. Compared with CK, straw interlayers decreased the stratification
ratios (0-20: 20-60 cm ) of SOC and TN contents by 5-15% and 4-9%,
respectively, which promoted a uniform distribution of SOC and TN
contents in 0-60 cm soil layer. Overall, straw interlayer with 12 Mg
ha-1 had higher SOC, TN, C:N ratio and lower soil
stratification ratio in 2015-2017, which contributed to salts leaching,
water retention, and yield increments. Our results highlighted the
legacy effects of straw interlayers on soil fertility and productivity
maintained more than four years associated with the amount of straw
input, which led to the underestimation for previous short-term
experiments. In conclusion, straw deep returning as interlayer was an
effective strategy to increase the subsoil nutrients, reduce soil
stratification ratio, and promote saline soil utilization.
Conflict of interest
We declare no competing interest.