3.3. C:N ratio
The relative changes of C:N ratio
compared to CK were higher in the early stage of straw interlayer burial
(2015-2016), especially in 20-40 cm and 40-60 cm depths, which increased
by 9-12% and 19-26%, respectively. Subsequently, the relative changes
of C:N ratio between straw interlayer treatments fluctuated slightly
(Figure 3c).
The C:N ratio increased at the beginning while subsequently decreased
with increasing soil depth (Figure 4c). In 2015, compared with CK, SL6,
SL12 and SL18 increased C:N ratio by 12, 17 and 9% in 20-40 cm soil
depth, and 36, 34 and 16% in 40-60 cm depth, respectively (p< 0.05). In 2016, compared with CK, straw interlayers
increased C:N ratio by 6-15% in 20-40 cm depth, SL12 and SL18 increased
C:N ratio by 17 and 21% in 40-60 cm (p < 0.05). In
2017, straw interlayers (6-18 Mg ha-1) boosted C:N
ratio by 8-11% and 6-9% in 20-40 cm and 40-60 cm depth compared with
CK, respectively. In 2018, C:N ratio increased with increasing amount of
straw interlayer, but no significant difference with CK.
3.4. Stratification
ratio s of SOC and TN
The stratification ratios of SOC and TN were influenced by straw
interlayers (p < 0.001) and experimental year (p< 0.01) (Figure 6). Compared to CK, straw interlayers
decreased the stratification ratios (0-20 cm: 20-60 cm) of SOC and TN by
5-15% (Fig. 6a) and 4-9% (Fig.
6b) (p < 0.05). In contrast, the stratification ratios
of SOC and TN for 0-20 cm: 60-80 cm showed an opposite trend.