Effects of cover cropping on the aggregate stability of Shajiang black soil and its organic carbon fractions

Abstract

为探究覆盖作物种植对淮北平原砂姜黑土团聚体稳定性和有机碳组分的影响，本研究以淮北平原砂姜黑土为研究对象，研究不压实及压实处理下不同覆盖作物类型（休闲、苜蓿、油菜、萝卜+毛苕子混播）对表层土壤（0~10 cm和10~20 cm）团聚体稳定性及其有机碳组分的影响。结果表明：与休闲相比，种植不同覆盖作物（苜蓿、油菜、萝卜+毛苕子）均能显著提高两种压实处理0~10 cm土层有机碳（SOC）含量，其中苜蓿处理增幅最大（14.3%）；在10~20 cm土层，仅苜蓿处理显著增加了SOC含量（9.17%~10.8%）。在0~10 cm和10~20 cm土层，各覆盖作物处理土壤水稳性团聚体平均质量直径（MWD）的变化规律与土壤有机碳完全一致，均表现为苜蓿处理显著提高了两个土层的MWD。与休闲相比，3个种植覆盖作物处理均能显著提高0~10 cm土层水稳性大团聚体（≥2 000 μm）的含量；10~20 cm土层中仅苜蓿处理在两种压实处理下水稳性大团聚体（≥2 000 μm）含量较休闲处理有显著提升。种植覆盖作物使不同粒级团聚体SOC含量均呈现出增加的趋势，其中苜蓿处理显著增加了0~10 cm和10~20 cm土层≥2 000、250~<2 000 μm和53~<250 μm团聚体SOC含量。与休闲处理相比，苜蓿、油菜和萝卜+毛苕子处理均显著增加了0~10 cm和10~20cm土层土壤颗粒有机碳（POC）含量，其中苜蓿处理的增幅均为最大（25.2%~34.5%）。覆盖作物对土壤矿物结合态有机碳（MOC）含量无显著影响。与不压实处理相比，压实处理对SOC、POC和MOC含量以及水稳性团聚体MWD均无显著影响。研究表明，种植覆盖作物尤其是苜蓿可以显著提高砂姜黑土总有机碳和颗粒有机碳含量以及水稳性团聚体的稳定性，从而改善砂姜黑土质量并提升其生产力。

This study investigated the effects of cover crops on aggregate stability and organic carbon fractions of the Shajiang black soil in the Huabei Plain. Four cover cropping treatments（fallow, alfalfa, oilseed rape, and radish with hairy vetch mixture）with or without compaction operations were used in this study. Soil samples were collected from layers at depths of 0-10 cm and 10-20 cm. Soil aggregate size distribution, soil organic carbon（SOC）, and its fractions（particulate organic carbon, POC, and soil mineral-associated organic carbon, MOC）were measured. The results showed that cover crops significantly increased SOC content in the 0-10 cm soil layer when compared with the fallow treatment（P<0.05）, particularly in the case of alfalfa treatment（14.3%）. Only the alfalfa treatment increased SOC in the 10-20 cm soil layer（9.17% - 10.8%, P<0.05）. The alfalfa treatment significantly enhanced mean weight diameter（MWD）in both soil layers compared with the fallow treatment. The three cover crop treatments significantly increased the amount of ≥2 000 μm aggregate in the 0-10 cm soil layer as compared with the fallow treatment, but no significant increase was observed in the 10-20 cm soil layer（with an exception of the alfalfa treatment）. The alfalfa treatment significantly increased SOC of aggregates ≥2 000, 250-<2 000 μm, and 53-<250 μm in both the soil layers. Cover crops significantly augmented the POC compared with the fallow treatment；the largest increase was found with the alfalfa treatment regardless of the soil layers（25.2%-34.5%）. Cover crops had no effects on MOC. Compaction had no effects on the SOC, POC, and MOC contents and MWD. The study showed that cover crops, particularly alfalfa, significantly boosted POC content and hence promoted SOC accumulation and aggregate stability, thus enhancing the Shajiang black soil quality.