旋耕转深松和秸秆还田增加农田土壤团聚体碳库

土壤耕作和秸秆还田能够显著影响土壤结构和养分周转,也是土壤团聚体分布及更新周转的主要驱动因素。该研究基于连续9 a的旋耕-深松定位试验,对比了长期旋耕农田转变为深松以及秸秆还田对农田土壤0~50 cm土壤团聚体分布、稳定性及团聚体碳含量的影响,分析了团聚体碳对土壤有机碳的贡献率及相互关系。研究结果表明,将长期旋耕农田转变为旋耕-深松农田显著影响了0~50 cm土层的团聚体分布及其碳含量。旋耕-深松配合秸秆还田(RTS-STS)模式能够显著提高表层土壤较大粒级团聚体的比例,且显著提高了土壤团聚体稳定性,分别比旋耕-深松无秸秆还田(RTA-STA)、旋耕秸秆还田(RTS)和旋耕无秸秆还田(RTA)处理高6.1%、65.4%和87.8%;同时,RTS-STS处理显著提高了0~20 cm土层团聚体碳含量和对有机碳的贡献率,虽然在20~30和30~50 cm土层之间,2个处理的团聚体碳含量差异并不明显,但RTS-STS处理的团聚体碳含量对有机碳的贡献率较0~20 cm土层和RTS处理显著降低。通过耕作方式转变、秸秆还田和两者的交互作用对土壤团聚体分布及其碳含量影响的作用力分析可看出,耕作、秸秆及其交互作用是影响不同土层中各处理在不同粒级团聚体分布比例及碳含量差异的主要因素。通过相关分析表明,土壤有机碳含量与团聚体稳定性及其自身碳含量之间存在显著或极显著的正相关关系。旋耕-深松配合秸秆还田(RTS-STS)模式促进了0~20 cm土壤团聚体的形成和稳定,提高了土壤团聚体碳库和对有机碳的贡献,对提升土壤有机碳水平具有积极意义。

Residue returning with subsoiling replacing rotary tillage improving aggregate and associated carbon

Abstract: Soil tillage and residue returning could exert significant impact on soil structure and nutrient turnover, which were also important driving factors for the distribution and update of soil aggregate. The objectives of this study were to estimate the effects of rotary tillage converting to subsoiling on distribution, stability and associated-C content of soil aggregate based on the 8-year experiment, which included rotary tillage with residue returning (RTS), rotary tillage with residue removing (RTA), rotary tillage converting to subsoiling with residue returning (RTS-STS) and rotary tillage converting to subsoiling with residue removing (RTA-STA). The contribution rate of aggregate-C to soil organic carbon (SOC) and their interaction during rotary tillage converting to subsoiling were also analyzed in this study. The results showed that, the distribution, stability and associated-C of soil aggregate fractions were significantly affected by rotary tillage converting to subsoiling combined with the returning of residue, which not only significantly increased the proportion of soil macroaggregate, but also promoted the stability of aggregate. For example, the aggregate fraction proportions of 1-2, 0.25-1 and <0.25 mm under RTS-STS treatment were significantly higher than those of other 3 treatments in the soil depth of 0-10 cm, and the mean weight diameter (MWD) for stability index of soil aggregate under RTS-STS treatment was also 6.1%, 65.4% and 87.8% higher than RTA-STA, RTS and RTA treatments respectively in this study. And the aggregate fraction proportions of 1-2, 0.25-1 and <0.25 mm under 4 treatments were increased in the soil depth of >30-50 cm compared with that in the soil depth of 0-30 cm. Whereas, the MWD values were significantly decreased under the RTS-STS and RTA-STA treatments in the soil depth of 30-50 cm, and the opposite result was found under RTS and RTA treatments. Meanwhile, RTS-STS treatment significantly increased aggregate associated-C and its contribution rate to SOC in the depth of 0-20 cm. Although there was no significant difference for aggregate associated-C between RTS-STS and RTS treatments in the depth of >20-30 and >30-50 cm, the contribution rate of aggregate associated-C to SOC was decreased under the RTS-STS treatment compared with that in >20-50 cm depth. In comparison to the residue removing, rotary tillage and rotary tillage converting to subsoiling combined with the returning of residue increased the contents of SOC and aggregate associated-C in the soil depth of 0-50 cm. The contribution rate of aggregate associated-C to SOC under RTS-STS treatment was 87.89%, which was 4.9%, 10.3% and 18.6% higher than RTS, RTA-STA and RTA treatments respectively in this study. Tillage method, residue returning and their interaction were important effect factors on the distribution and associated-C of soil aggregate under 4 treatments in the different soil depths according to the force analysis in this study. Additionally, there was significant positive correlation between the SOC and the stability and associated-C(P<0.01) of aggregate by the correlation analysis. The tillage converting combined with residue returning (RTS-STS) can improve the aggregate gathering and stabilizing in the 0-20 cm soil depth, and also increase the contribution rate of soil aggregate associated-C to SOC, which would significantly improve the SOC level in this region.