土地利用方式对土壤团聚体稳定性和有机碳含量的影响

探究不同土地利用方式下土壤团聚体的粒径分布、稳定性及有机碳在各粒径团聚体中的分布规律,以期为重庆地区土壤结构的改善及土壤有机碳库的维持及提高提供依据.以重庆市北碚区6种土地利用方式(针阔叶混交林、竹林、果园、旱地、水田和荒草地)为研究对象,采用湿筛法对土壤进行粒径分组,对比分析了6种土地利用方式处理下土壤团聚体和团聚体有机碳在0～20、20～40、40～60和60～100 cm土壤剖面中的分布规律.结果表明,不同土地利用方式下,土壤的结构和肥力水平存在显著的差异.在0～100 cm土层土壤的各粒径团聚体中,6种土地利用方式的团聚体粒径均以 0. 25 mm为主;其中,竹林 0. 25 mm团聚体含量最高,其次是荒草地,旱地与果园含量最低.不同土地利用方式下0. 25～2 mm的粒径团聚体主要分布在0～20 cm土层(28. 78%～50. 08%),而0. 053～0. 25 mm和0. 053 mm的粒径团聚体主要集中在40～60cm土层.在整个土壤深度内,竹林和荒草地的土壤团聚体MWD和GMD均高于其他土地利用方式,即二者的土壤团聚体稳定性较强.土壤团聚体稳定性与土壤团聚体有机碳呈极显著正相关(r=0. 569,P 0. 01),在0～100 cm土层中,土壤0. 25～2 mm和0. 053 mm粒径的有机碳含量较高,其中0. 25～2 mm的最高,平均含量为56. 54 g·kg~(-1).除旱地土壤各粒径团聚体有机碳含量在20～40 cm土层内最高,其他土地利用方式下土壤各粒径团聚体内有机碳含量均随土壤深度的增加而降低,表现出显著的表层富集现象.总体上,6种土地利用方式下,竹林和荒草地在各土层中的土壤团聚体稳定性较好,且在各土层中,竹林土壤各粒径团聚体有机碳含量最高.

Effects of Land Use Type on the Content and Stability of Organic Carbon in Soil Aggregates

The distribution and stability of soil aggregates under different land use types, and the distribution of organic carbon in various aggregates, were explored in order to provide a basis for the improvement of soil structure and the maintenance and improvement of soil organic carbon in Chongqing. Focusing on six representative subtropical land use types in the Beibei District of Chongqing (coniferous and broadleaf mixed forest, bamboo forest, orchard, dryland, paddy field, and waste grassland), soils were sorted using the wet sieving method and the six soil types were compared and analyzed. The distribution of aggregates and their organic carbon content were determined at soil profile depths of 0-20, 20-40, 40-60, and 60-100 cm for each land use type. The results showed that there were significant differences in soil structure and fertility levels under the different land use types. Among the particle size aggregates of the 0-100 cm soil layer, the aggregate particle size of the six land use types was mainly >0.25 mm; the content of >0.25 mm aggregate fraction of bamboo forest soil is the highest, followed by the grassland soil, and the dryland and orchard soils is the lowest. Granular aggregates in the size class 0.25-2 mm were mainly distributed in the 0-20 cm soil layers (28.78%-50.08%), while the aggregate size fractions 0.053-0.25 mm and<0.053 mm were mainly concentrated in the 40-60 cm soil layers. Across the entire profile depth, the aggregate MWD and GMD of the bamboo forest and barren grassland soils were higher than the other land use types, i. e., the soil aggregates in these soils were more stable. The stability of soil aggregates was significantly positively correlated with soil aggregate organic carbon content (r=0.569, P<0.01). In the 0-100 cm soil layer, the organic carbon content of soil aggregates was higher for the 0.25-2 mm and<0.053 mm fractions, with an average content of 56.54 g·kg^-1 in the 0.25-2 mm fraction. Except for the organic carbon content of the soil aggregates with different particle size of dryland was the highest in the 20-40 cm soil layer, while under the other land use types, the organic carbon content in soil aggregates decreased with depth, showing significant surface enrichment. Overall, under the six different land use types, the soil aggregates in bamboo forest soils and waste grassland soils showed good stability, and at each soil depth, the organic carbon content of aggregates was highest in the bamboo forest soil.