绿洲农田土壤团聚体组成及有机碳和全氮分布对秸秆还田方式的响应

Response of composition of soil aggregates and distribution of organic carbonand total nitrogen to straw returning in an oasis area

通过田间定位试验,在甘肃干旱灌区,研究了不同小麦秸秆还田方式(NTSS: 25~30 cm 高茬收割立茬免耕;NTS: 25~30 cm高茬秸秆覆盖免耕;TIS: 25~30 cm 高茬秸秆深翻耕;CT:传统不留茬深翻耕—对照)对农田土壤团聚体及有机碳和全氮分布特征的影响,以期为优化试区种植模式与提高农业可持续发展提供依据。结果表明:免耕秸秆还田处理(NTSS、NTS)≥0.25 mm团聚体含量较高,与CT相比,在0~10、10~20、20~30 cm土层分别提高5.4%与12.5%、13.3%与14.1%、11.1%与19.2%,以NTS提高幅度较大。NTSS、NTS提高了0~10、20~30 cm土壤团聚体的平均重量直径,较CT处理分别提高6.7%与11.6%、7.6%与8.1%,以NTS提高效果最明显。NTSS、NTS处理土壤有机碳和全氮含量均高于 CT 处理,在0~10、10~20、20~30 cm土层,有机碳含量分别增大8.1%与13.3%、7.4%与11.4%、7.8%与12.8%;全氮含量分别提高14.6%与17.9%、14.5%与17.9%、16.2%与20.5%,同样,以NTS提高土壤有机碳及全氮程度较大。各级别团聚体中有机碳和全氮含量均随土层深度增加而减小,团聚体中有机碳和全氮含量随团聚体直径减小而增加,NTS处理在各土层各级别团聚体均保持较高的土壤有机碳及全氮含量。因此,前茬小麦25~30 cm秸秆覆盖免耕还田是干旱灌区增强土壤团聚体形成、提高土壤有机碳及全氮含量的适宜栽培措施。

A field experiment was carried out in arid irrigation regions to determine the effects of different wheat straw retention approaches on distribution characteristics of organic carbon and total nitrogen of soil aggregates in farmland, including (i) no tillage with 25 to 30 cm high straw standing (NTSS);(ii) no tillage with 25 to 30 cm high straw covering (NTS);(iii) conventional tillage with 25 to 30 cm high straw incorporation (TIS);and (iv) conventional tillage without straw retention (CT, the control).The results showed that no-tillage with straw retention (i.e., NTSS, NTS) had higher content of soil aggregates ≥ 0.25 mm than that of CT treatment, NTSS increased the content of soil aggregates ≥ 0.25 mm by 5.4%, 13.3%, and 11.1% in 0~10 cm, 10~20 cm, 20~30 cm soil depth, respectively and NTS increased it by 12.5%, 14.1%, and 19.2% in three soil depths, respectively.In particular, NTS treatment had the greatest effect on increasing content of the soil aggregates.NTSS and NTS treatments increased the average weight diameter (MWD) of soil aggregates by 6.7% and 7.6% in 0~10 cm and by 11.6% and 8.1% in 20~30 cm soil, respectively, in comparison to CT.NTS treatment had the highest increasing effect on the MWD.NTSS and NTS treatments improved soil organic carbon and total nitrogen contents;NTSS improved soil organic carbon by 8.1%, 7.4%, and 7.8%, improved total nitrogen by 14.6%, 14.5%, and 16.2% in 0~10 cm, 10~20 cm, and 20~30 cm soil, respectively.Similarly, NTS improved soil organic carbon by 13.3%, 11.4%, and 12.8%, improved total nitrogen by 17.9%, 17.9%, and 20.5% in three soil depths, respectively;and NTS treatment had the highest increasing percentage on soil organic carbon and total nitrogen.The contents of soil organic carbon and total nitrogen in different sized soil aggregates were decreased with increasing soil depth.The contents of soil organic carbon and total nitrogen of soil aggregates were increased with decreasing size.In all, NTS treatment had higher contents of soil organic carbon and total nitrogen in various soil depths and sizes.Therefore, our results indicated that no-tillage with 25 to 30 cm height of straw covering is recommended as the feasible farming method to enhance the formation of soil aggregates and improve the contents of soil organic carbon and total nitrogen in the arid oasis region.