3.1. Soil Organic Carbon (SOC)
The relative changes of SOC content compared to CK were
influenced by straw interlayers,
and experimental year × straw interlayers interaction (p< 0.05) (Figure 3a). The relative changes of SOC content were
decreased with the experimental years for SL6 and SL12, while it was
increased with the experimental years for SL18. The highest SOC changes
were found in 20-40 cm and 40-60 cm depths with 14-32% and 11-57%,
respectively. In the first two years of straw interlayer burying, the
relative change of SOC of each soil layer was the largest in SL12, but
in later years SL18 showed an advantage. In 2018, the relative change of
SOC under SL18 was the largest among all treatments.
The SOC content gradually decreased with deeper soil layers and
increased in the straw interlayers (p < 0.05) (Figure
4a). In 2015, the SOC content in SL12 with the greatest magnitude and
increase by 19-57% (p < 0.05) compared with no straw
interlayer. In 2016, the SOC content of straw interlayers was
significantly increased by 24-31% and 32-35% (p <
0.05), respectively at the depths of 20-40 cm and 40-60 cm, compared
with CK. Straw interlayer burial late stage (2017-2018), the SOC content
of SL18 were higher than other treatments, and the largest increase was
found in the depths of 20-40 cm and 40-60 cm.
Straw interlayers significantly affected SOC storage (p< 0.05) (Figure 5a). Compared with CK, SL6, SL12 and SL18
increased SOC storage by 8-22%, 14-34%, and 16-23% in 0-80 cm soil
depth from 2015 to 2018, respectively. The SOC storage in SL12 with
greatest magnitude among all straw treatments in 2015-2017.