Optimized straw interlayer improves organic carbon and total nitrogen in
soil profile: A four-year experiment in a saline soil
Abstract
Soil salinization is a critical environmental issue restricting
agricultural production. Straw deep returning as interlayer (40 cm) has
been a popularized practice to alleviate salt stress. However, the
legacy effects of straw interlayer associated with the straw input
amount on soil organic carbon (SOC) and total nitrogen (TN) in saline
soil remain unclear. Therefore, a four-year (2015-2018) field experiment
was conducted with four levels (i.e., 0, 6, 12 and 18 Mg ha
-1) of straw returning as interlayer. Compared with no
straw interlayer (CK), straw interlayers increased SOC content by
14-32% and 11-57% in 20-40 cm and 40-60 cm, respectively. Lower
increases were for soil TN content (8-22% in 20-40 cm and 6-34% in
40-60 cm) than SOC content, which led to increase soil C:N ratio in the
20-60 cm soil depth. Compared with CK, remarkable increases of SOC and
soil TN contents in 20-60 cm led to the decrease of stratification
ratios (0-20: 20-60 cm), which promoted uniform distributions of SOC and
TN in soil profiles. Even though soil parameters ranged widely according
to the straw input, 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 salt leaching, water retention, and
yield increment. These results highlighted the legacy effects of straw
interlayers maintained more than four years, which led to an
underestimation for previous short-term experiments, and demonstrated a
great potential for subsoil fertility and salt-affected soil
amelioration.