Reasonable rotation is of great significance to grassland management. We examined the distribution characteristics, stability, organic carbon content and contribution rate of 0-30 cm soil aggregates in the forbidding grazing, continuous grazing, and rotation in the two-paddock, four-paddock and six-paddock rotational districts in a desert steppe in Ningxia. The results showed that except for the forbidding grazing grassland that was dominated by mechanically stable large aggrega-tes, other water-stable aggregates were mainly composed of microaggregates. Increasing the rotational grazing zoning was conducive to maintain the content of water-stable aggregates in the surface soil and increase the content of large aggregates. The mechanical stability aggregate fractal dimension was the largest in continuous grazing, increased the fractal dimension of the rotation and shepherd partition to reduce the trend, but the fractal dimension of water-stable aggregates did not change. The average weight diameter (MWD) and geometric mean diameter (GMD) of the aggregates were the largest in the pastoral grassland and increased with the increases of the rotational grassland partition. MWD and GMD were negatively correlated with the microaggregate content. The organic carbon content in water-stable large aggregate was higher in the six-paddock rotational district and forbidding grazing, and the two-paddock rotational grazing and continuous grazing were lower. The contribution rate of micro-aggregates organic carbon to soil organic carbon content was higher in this region. In the 0-20 cm soil layer, the contribution rate of organic carbon in large aggregates increased with the increases of rotation. Considering the characteristics of soil aggregates and their organic carbon, the rotation of six-paddock was the most suitable method for rotational grazing in the desert steppe of the study area.
合理的草地轮牧方式对草原的科学管理具有重要意义.以宁夏荒漠草原为研究对象,对围封禁牧、连续放牧和二区、四区及六区轮牧下0~30 cm土层土壤团聚体分布特征、稳定性、有机碳含量及其贡献率进行了研究.结果表明: 除围封禁牧草地以机械稳定性大团聚体为主外,其他处理的土壤水稳性团聚体均以微团聚体为主;增加轮牧分区有利于表层土壤水稳性团聚体含量的保持及大团聚体含量增加.机械稳定性团聚体分形维数在连续放牧下最大,增加轮牧分区则呈现减小趋势,但水稳性团聚体分形维数无明显变化规律;团聚体平均重量直径(MWD)及几何平均直径(GMD)在禁牧草地最大,且随着轮牧分区的增加而增大;MWD和GMD与微团聚体含量呈显著负相关.水稳定性大团聚体有机碳含量以六区轮牧和围封禁牧较高,二区轮牧和连续放牧较低;试验区微团聚体有机碳对土壤有机碳含量贡献率较高,但0~20 cm土层中,轮牧分区越多则大团聚体有机碳贡献率越高.从土壤团聚体及其有机碳特征考虑,六区轮牧为研究区荒漠草原最适宜的轮牧方式.
Keywords: aggregate organic carbon; desert steppe; rotation method; soil aggregate.