抛荒对冷浸稻田土壤团聚体及有机碳稳定性的影响

Effects of land abandonment on soil aggregate and organic carbon stability in cold waterlogged paddy fields

冷浸稻田是长江流域重要的低产稻田类型之一,近年来抛荒严重,而抛荒对冷浸稻田土壤团聚体的影响并不清楚。本研究以连年种植的冷浸稻田（CWC）、抛荒3年的冷浸稻田（CWA3）和抛荒6年的冷浸稻田（CWA6）为对象,分析抛荒后冷浸稻田土壤团聚体特征以及有机碳稳定性,以期为准确评估抛荒对长期淹水土壤的结构和有机碳的影响提供数据支持。结果表明,不论是0～25 cm土层还是25～50 cm土层,冷浸稻田土壤＜53μm粒级团聚体占总团聚体比例均超过40%；0～25 cm土层土壤＞250μm团聚体比例超过35%；53～250μm粒级团聚体比例低于20%。抛荒使0～25 cm土层＆lt;53μm粒级团聚体占总团聚体比例显著增加,53～250μm粒级比例显著降低。在0～25 cm土层,抛荒使有机碳活性指数Ⅰ（LIc-Ⅰ）在＜53μm粒级和＞250μm粒级上升高,有机碳活性指数Ⅱ（LIc-Ⅱ）在53～250μm和＞250μm粒级上降低；而有机碳难降解指数（RIc）在＜53μm和53～250μm粒级上降低。土壤总有机碳随抛荒时间延长而增加。

Soil structure, which is decided by the stability of soil aggregates to a great extent, significantly influences soil environ-ment. Soil aggregates are secondary particles formed through the combination of particulate minerals with organic and inorganic substances. Soil organic carbon is critical for enhancing soil quality and sustainable production. Even a slight increase in soil organic carbon content could induce a substantial sequestration of excess atmospheric CO2. Cold waterlogged paddy field is one form of low-productivity paddy fields in the central China. This type of paddy field is especially common in the middle and lower reaches of Yangtze River Basin. In recent years, large areas of cold waterlogged paddy fields have been abandoned due to high labor costs and low returns. Due to long-term floods, cold waterlogged paddy fields have very poor soil structures that are often described as mushy soils. Not only is the composition of aggregate proportions and organic carbon of marshy soils are vastly different from that of ordinary paddy fields, the aggregate sizes and organic carbon stability of marshy soils are unclear. It is also not clear how soil structure and organic carbon changed after cold waterlogged paddy field was abandoned. In this study, we investigated the effects of land abandonment on soil total organic carbon, soil aggregation fractions and organic carbon content in cold waterlogged paddy fields under continuous rice cultivation （CWC）, abandoned for three years （CWA3） and abandoned for six years （CWA6）. The results showed that the aggregate compositions were dominated by 〈53 μm particles, accounting for over 40% of the soil in cold waterlogged paddy fields. Then＆gt;250μm particles accounted for over 35%and 53？250μm particles accounted for less than 20%of the 0–25 cm soil layer in cold waterlogged paddy fields. Land abandonment significantly increased the〈53μm aggregate fraction and decreased the 53–250μm aggregate fraction in the 0–25 cm soil layer. Also land abandonment improved labile organic carbon poolⅠindex （LIc-Ⅰ） of the〈53 μm and〉250μm soil aggregates, decreased labile organic carbon poolⅡindex （LIc-Ⅱ） in the 53–250 μm and〉250 μm soil aggregates, and reduced recalcitrant organic carbon index （RIc） in the〈53μm and 53–250μm soil aggregates. Soil total organic carbon increased with increasing length of period of land abandonment.