深松和秸秆还田对旋耕农田土壤有机碳活性组分的影响

土壤有机碳(soil organic carbon,SOC)及其活性组分能够敏感响应耕作方式变化及有机物输入。为对比长期旋耕农田进行深松后土壤有机碳各活性组分及比例变化,该研究基于连续7a的旋耕转变为深松和秸秆管理长期定位试验,对比了旋耕无秸秆还田处理(rotary tillage with straw removal,RT)、旋耕秸秆还田处理(rotary tillage with straw return,RTS)、旋耕转变为深松无秸秆还田处理(rotary tillage conversion to subsoiling with straw removal,RT-DT)、旋耕转变为深松秸秆还田处理(rotary tillage conversion to subsoiling with straw return,RTS-DTS)下土壤有机碳(soil organic carbon,SOC)、颗粒有机碳(particulate organic carbon,POC)、易氧化有机碳(readily oxidizable organic carbon,ROC)、微生物生物量碳(microbial biomass carbon,MBC)、溶解性有机碳(dissolved organic carbon,DOC)、活性有机碳(labile organic carbon,LOC)在土壤有机碳中比例的变化及各组分间的相互关系。研究结果表明,耕作方式从旋耕转变为深松和秸秆还田对SOC及其各活性组分均产生显著影响,耕作方式转变、秸秆还田及两者的交互效应是影响SOC及其活性组分的主要因素。秸秆还田显著提高了RTS处理和RTS-DTS处理的SOC含量,分别比RT和RT-DT处理高6.1%~15.6%和19.1%~32.3%。并且转变耕作方式后RTS-DTS处理比于RTS处理SOC含量提高16.9%~20.0%。同时,RTS-DTS处理的POC含量比RTS处理高13.6%~53.8%;但RT-DT和RTS-DTS处理的土壤ROC含量较RT和RTS处理都呈下降趋势,RTS-DTS处理的ROC含量比RTS处理下降4.6%~10%;MBC含量降低23.8%~30.6%。虽然秸秆还田显著提高了各处理的DOC含量,但RTS转变为RTS-DTS处理后,其3个土层的DOC含量下降了8%~41%。相比于RT和RTS处理,RT-DT和RTS-DTS处理0~30 cm各土层中LOC在SOC中的比例显著下降。相关性分析结果表明,除POC与ROC之间无显著性相关关系外,SOC及各组分间均呈显著(P<0.05)或极显著(P<0.01)的相关关系。耕作方式转变为深松和秸秆还田提高了SOC含量的同时,显著降低了SOC中的活性有机碳组分,这更有利于SOC的有效积累,促进土壤碳库的稳定固存。

Effects of subsoiling and straw return on soil labile organic carbon fractions in continuous rotary tillage cropland

Abstract: Soil organic carbon (SOC) and its labile carbon fractions (LOC) including particulate organic carbon (POC), readily oxidized organic carbon (ROC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), can sensitive response to tillage method change and organic matters input. We compared the contents changes of SOC, POC, ROC, MBC, DOC and their correlations, and analyzed change in the proportion of LOC fractions in soil organic carbon (LOC/SOC), based on a 7 years old experiment for tillage method change and straw management including the rotary tillage with straw removal (RT), rotary tillage with straw return (RTS), rotary tillage conversion to subsoiling with straw removal (RT-DT) and rotary tillage conversion to subsoiling with straw return (RTS-DTS). The results showed that SOC contents in the depths of 0-10 and >10-20 cm under RTS-DTS increased by 16.9% and 20.0% compared with those of RTS treatment, respectively; while there had no significant difference on SOC in the depth of >10-20 cm between RTS-DTS and RTS treatments. Compared with the RT and RT-DT treatments, SOC content was increased 6.1%-15.6% and 19.1%-32.3% by the RTS and RTS-DTS treatments in three soil layers. POC contents increased after rotary tillage conversion to subsoiling awith straw return, its contents under RTS-DTS treatment in the 0-10, >10-20 and >20-30 cm soil depths were high 53.8%, 30.7% and 13.6% than those of the RTS treatment, respectively. POC contents were increased 36.8%, 24.5% and 34.0% by RTS-DTS in comparison to RT-DT. The highest POC content was generally observed at the 0-10 cm soil depth in each treatment. These differences of POC contents were significant affected by soil tillage (23.8%-63.0%), straw management (24.2%-72.4%) and their interaction effect (2.6%-25.1%). Compared with the RTS treatment, whereas, the contents of ROC, MBC and DOC were decreased by RTS-DTS in three soil depths. Soil ROC in the 0-10, >10-20 and >20-30 cm soil depths under RT-DT treatment were declined 19.9%, 13.0% and 67.9% than those of RT treatment, and their contents under RTS-DTS treatment were declined with 6.6%, 10.0% and 4.6% than those of RTS treatment, respectively. These decreases were significant related with the tillage method change and straw return (P<0.05). The straw return increased ROC contents in the 0-30 cm soil layers and the content was decreased with the deepening of soil depth. Compared with the RTS treatment, soil MBC contents in three soil depths were decreased 23.9%, 30.6% and 23.8% by RTS-DTS, respectively. Although soil DOC content was increased after crop straw return, the contents were significant decreased by the tillage method change (P<0.05). For example, DOC content was declined 8%-41% by the RTS converting to RTS-DTS. There had significant positive correlations between SOC and POC (r=0.87, P<0.01), ROC (r=0.82, P<0.01), DOC (r=0.55, P<0.05), MBC (r=0.68, P<0.05). Meanwhile, there were significant positive correlations among soil POC and ROC (r=0.75, P<0.01), POC and MBC (r=0.66, P<0.05), ROC and DOC (r=0.75, P<0.01), ROC and MBC (r=0.77, P<0.01), DOC and MBC (r=0.65, P<0.05). The proportions of LOC/SOC were significant decreased by RT-DT and RTS-DTS. Rotary tillage conversion to subsoiling with straw return could increase the SOC and POC content while decrease ROC, MBC, DOC fractions and LOC/SOC proportions, which would advantage to accelerate accumulation and stability for SOC pool.