耕作方式转变和秸秆还田对土壤活性有机碳的影响

深松是解决长期旋免耕后耕层浅薄化、亚表层(15~30 cm)容重增加等问题的有效方法之一,长期旋免耕后进行深松显著影响土壤有机碳及其组分的周转。为对比转变耕作方式对土壤活性有机碳(LOC)及碳库管理指数的影响,该研究基于连续6 a的旋耕转变为深松和免耕转变为深松定位试验,对比了2012-2014年长期旋免耕农田进行深松对农田土壤活性有机碳及碳库管理指数的影响。研究结果表明,耕作方式转变和秸秆还田均对土壤LOC含量、活性有机碳与有机碳的比例(LOC/SOC)和碳库管理指数产生显著影响。相对于原旋耕秸秆还田处理(RTS),虽然旋耕-深松秸秆还田处理(RTS-STS)提高了0~30 cm土层的LOC含量,但其土壤中LOC/SOC比例和碳库管理指数显著下降。而免耕-深松秸秆还田(NTS-STS)处理和耕作方式未转变的免耕秸秆还田处理(NTS)在0~10 cm土层其LOC含量无显著性差异,但NTS-STS处理显著提高LOC/SOC比例。耕作方式转变导致RTS-STS处理碳库管理指数随着土层的加深而逐渐降低,而NTS-STS处理则呈逐渐升高趋势。耕作、秸秆、年份、耕作与秸秆、耕作与年份及3者交互作用是导致耕作方式转变后各处理0~30 cm的LOC含量变化的主要作用力(P0.05)。秸秆还田条件下,将长期旋耕处理转变为深松可显著降低土壤SOC中的LOC比例,降低碳库管理指数,促进土壤碳库的稳定性;而长期免耕处理转变为深松能够显著提高土壤下层(10~30 cm)的土壤碳库活性。

Effect of tillage method change and straw return on soil labile organic carbon

Abstract: Subsoiling is an important method to solve the problem of subsoil compaction in 15-30 cm depth due to the increase of bulk density or the decrease in porosity after long-term no tillage or rotary tillage. Although subsoiling is of growing concern in Chinese agriculture production system and it could significantly influence the different fractions in soil carbon pool, there are few information on soil labile organic carbon (LOC) and carbon pool management index response to the conversion from long-term no tillage and rotary tillage to subsoiling in the North China Plain. The objective of this study was to estimate the changes in soil LOC content, the ratio of LOC fraction to soil organic carbon (LOC/SOC), and the soil carbon pool management index (CMI) by six-year tillage method change experiment. The experimental treatments including rotary tillage with residue removal (RTA), rotary tillage with residue return (RTS), rotary tillage converting to subsoiling with residue removal (RTA-STA), rotary tillage converting to subsoiling with residue return (RTS-STS), no tillage with residue removal (NTA), no tillage with residue return (NTS), no tillage converting to subsoiling with residue removal (NTA-STA), no tillage converting to subsoiling with residue return (NTS-STS). The results showed that tillage method changes significantly impacted soil LOC, LOC/SOC and soil CMI in this study. In comparison to RTS treatment, RTS-STS increased the content of soil LOC in the 0-30 cm depth, but the LOC/SOC ratio and soil CMI declined. However, soil LOC content was decreased in the 0-10 cm layer while increased in the 10-20 cm layer. Meanwhile, soil LOC contents under the RTS-STS and NTS-STS treatments were significant higher than that of the RTA-STA and NTA-STA treatments. Tillage and residue factors played a key role for the change of soil LOC content in different layers (P<0.05). Soil LOC/SOC also presented a significant difference after tillage method changed. For the RTA-STA and RTS-STS treatments, the ratio of LOC to SOC declined in the 0-30 cm layer (P<0.05). Although there was no significant difference on soil LOC/SOC between NTA-STA and NTS-STS treatments in the 0-10 cm layer, the LOC/SOC value under NTS-STS treatment was great higher than that of NTA-STA treatment in the 10-30 cm layer (P<0.05). Observations of soil CMI declined with the deepening of soil layers after RTS was converted to RTS-STS, but the opposite result was showed after NTS was converted to NTS-STS. Tillage, crop residue, experiment years and their interactions significantly affected the soil LOC after tillage method changed according to a multi-way ANOVA (analysis of variance) analysis (P<0.05). The conclusions are drawn that soil LOC, LOC/SOC and soil CMI can be decreased by long-term RT converting to RT-ST, which will promote soil carbon sequestration, but the adopting of NT converting to NT-ST might enhance the activity of soil carbon pool in the 10-30 cm depth.