3.2 Total Nitrogen (TN)
The relative changes of TN content compared to CK in 0-60 cm soil depth were significantly influenced by straw interlayers (p < 0.01), and experimental year ×straw interlayers interaction (p< 0.01) (Figure 3b). Straw interlayers (6-18 Mg ha-1) increased TN content by 8-22% and 6-34% in 20-40 cm and 40-60 cm depth compared with CK. The relative changes of TN content were the largest under SL12 in the first three years of straw interlayer burial (2015-2017) but under SL18 in 2018.
Straw interlayers (SL6, SL12 and SL18) increased TN content (Figure 4b). In 2015, SL12 had the highest TN content, with an increase of 13 and 17% in 20-40 and 40-60 cm depths as compared to CK (p< 0.05), respectively. Similarly, in 2016, compared with CK, the TN content in SL6 and SL12 increased by 18 and 22% in 20-40 cm, and 23 and 15% in 40-60 cm (p < 0.05). In 2017, the changes of TN content relative to CK in SL12 and SL18 increased with the deepening soil layer, with the increase of 16-22% and 13-34%. In 2018, SL18 had the highest TN content compared with other treatments.
Straw interlayers significantly increased TN storage (p< 0.05) (Figure 5b). Compared with CK, straw interlayers increased TN storage by 6-17% in 2015-2018 (p < 0.05).