覆盖方式对旱作小麦田土壤团聚体有机碳的影响

依托中国科学院长武黄土高原农业生态实验站的长期覆盖试验,分析研究秸秆覆盖和地膜覆盖对黄土高原旱作冬小麦田土壤团聚体分布和团聚体有机碳的影响,共包括4种处理:无覆盖(CK)、全年9 000 kg·hm~(-2)秸秆覆盖(M_(9000))、全年4 500 kg·hm~(-2)秸秆覆盖(M_(4500))和全年地膜覆盖(PM)。结果表明:(1)与CK处理相比,M_(9000)处理土壤总有机碳含量提高8.1%(P0.05),M_(4500)和PM处理较CK处理无显著差异。(2)M_(9000)、M_(4500)处理0.25 mm团聚体含量较CK处理分别提高6.6%、4.1%,PM处理降低1.7%。(3)与CK处理相比,M_(9000)处理平均重量直径(MWD)值提高9.2%,PM处理降低14.8%;M_(9000)处理几何平均直径(GMD)提高13.0%,PM处理降低15.7%(P0.05)。(4)土壤总有机碳与0.25 mm团聚体含量、MWD和GMD值呈显著正相关。(5)各处理中,5 mm和0.25 mm团聚体中有机碳含量较高;M_(9000)处理可不同程度地提高各级别团聚体中有机碳的含量,PM处理作用不明显;土壤有机碳主要储存在机械稳定性大团聚体中,且5 mm团聚体对总有机碳的贡献率最大,M_(9000)、M_(4500)处理可提高0.25 mm团聚体有机碳的贡献率。(6)各处理土壤总有机碳与5 mm和0.25 mm机械稳定性团聚体中有机碳呈极显著正相关。因此,长期秸秆覆盖不仅可以提升团聚体水平和稳定性,还可增加团聚体中有机碳含量,有利于土壤有机碳的固定。该区全年9 000 kg·hm~(-2)秸秆覆盖处理效果最好。

Effects of different mulching treatments on the soil organic carbon content in soil aggregates in a rainfed wheat field

To investigate the effects of different mulching treatments on soil aggregate distribution and the content of soil organic carbon in soil aggregates four mulching measures were conducted including CK (without mulching treatment),M9ooo (straw mulching at a rate of 9 000 kg· hm-2),M4500 (straw mulching at rate of 4 500 kg· hm-2),and PM (plastic film mulching) in a rainfed winter wheat field on Loess Plateau.The results showed that compared with CK,soil total organic carbon (TOC) content by Mg00o was increased by 8.1％ (P ＜ 0.05).TOC content by M4500 and PM had no significant differences.Compared with the CK treatment,soil mechanical-stable macroaggregates content became increased by 6.6％ and 4.1％ by M9000 and M4500 treatments,respectively.PM treatment macroaggregates content was significantly decreased by 2.5％ compared with CK.Compared with CK,the soil mean weight diameter (MWD) by M9000 treatment was increased by 9.2％,and was decreased by 14.8 ％ by PM treatment.The soil geometric mean diameter (GMD) byMg000 treatment was increased by 13.0％,and became decreased by 15.7％ (P ＜ 0.05) by PM treatment.TOC has close relationships with soil macroaggregate content,MWD and GMD.TOC could increase mechanical-stable aggregates and enhance the stability.Additionally,TOC was mainly concentrated in aggregates with the agglomeration ＞ 5 mm and ＜ 0.25 mm size.M9000 treatment could improve the organic carbon of all the mechanical-stable aggregates size at different degrees,but PM treatment had no effects.Soil organic carbon was mainly stored in the mechanical-stable macroaggregate.＞ 5 mm size aggregate contribution is the largest within the total soil organic carbons.M9000 and M4500 treatments could improve the contribution rate of the ＞ 0.25 mm size aggregates.Furthermore,there was a significant positive correlation between TOC and ＞ 5 mm,＜ 0.25 mm aggregates organic carbon,indicating that ＞ 5 mm and ＜ 0.25 mm aggregates could be used as a proxy for measuring changes in soil organic carbon.Therefore,straw mulching could not only enhance the aggregate content and stability,but also increase the organic carbon content in aggregate,which is beneficial for soil carbon sequestration with an optimal treatment rate at 9 000 kg· hm-2.