黄土高原不同草地类型对水稳性团聚体粒径分布及稳定性的影响

Effects of different grassland types on particle size distribution and stability of water stable aggregate on the Loess Plateau

本研究在甘肃兰州选择了4种不同类型的人工草地与天然草地为研究对象,分别为苜蓿草地、冰草草地、柠条灌木草地及针茅草地,其中针茅草地为天然草地。分析了4种草地类型0~40cm土层的土壤水稳性团聚体粒径分布特征、平均重量直径(mean weight diameter,MWD)以及它们之间的差异性和相关性。结果表明,>2mm和<0.25mm粒径的水稳性团聚体为优势粒径;在土壤表层0~20cm,针茅草地>0.25mm粒径的水稳性团聚体显著高于其他草地类型(P<0.05),而在20~40cm土层,苜蓿草地最高,说明在表层针茅草地对土壤结构的改良最优,随土层加深苜蓿草地对土壤结构的改良效果突出;苜蓿草地MWD值由表层0~10cm的1.04mm降低到30~40cm的0.72mm,下降了31%,而其他草地类型下降了50%~80%,说明苜蓿草地对不同层次土壤结构改良效果的差异性最小。MWD值与>0.25mm粒径的水稳性团聚体含量和有机质呈极显著的正相关关系,与土壤容重呈极显著的负相关关系,表明水稳性大团聚体和有机质含量的增加可有效促进土壤结构的改良,加强土壤结构的稳定性,提高土壤的抗侵蚀能力。

Vegetation restoration can promote the formation of soil aggregates. The stability of soil structure is related to the water-stable aggregate content. The higher the content of water-stable aggregates, the more is the improvement in the soil erosion-resistance. Different plants have different effects on the water-stable aggre- gate component of soils. To evaluate the stability of soil structure under different grasslands, we studied differ- ent artificial grasslands and natural grasslands, including Medicago sativa, Agropyron cristatum, Caragana korshinskii and Stipa capillata in Lanzhou city, Gansu province. A soil aggregate analyzer was used to meas- ure the size distribution of water-stable aggregates. The aggregate size differences and correlation of particle size distribution and mean weight diameter （MWD） of water-stable aggregate of the four different grasslands were analysed for the 0-40 cm soil depth. The results showed that the most abundant particle size of water- stable aggregates was 〉2 mm or d0.25 ram. For the 0-20 cm depth the proportion of water-stable aggregates of 〉0. 25 mm particle size in S. capillata grassland was significantly higher than other grasslands （P〈 0.05）. For the 20-40 cm depth, the proportion of water-stable aggregates of 〉0.25 mm particle size was highest in M. sativa grassland. Hence, S. capillata grassland had the most improved soil structure for the 0- 20 cm depth, while the M. sativa grassland had a better effect on soil structure at greater depth in the soil pro- files. The MWD value for soil samples from M. sativa grassland decreased 31% from 1.04 mm in the 0--10 cm depth to 0.72 mm in 30--40 cm soil depth. These results indicate that in M. sativa grassland, soil struc- ture improvement does not greatly differ between soil depths. There were extremely significant correlations be- tween the MWD value, the proportion of water-stable aggregate in 〉0. 25 mm particle size category and soil organic matter content. Generally, the MWD value and soil bulk density were significantly and negatively cor- related. The results demonstrate that increase in the proportion of soil water-stable macro-aggregate and soil organic matter are effective ways to promote soil structure improvement, and enhance soil structure stability and resistance to erosion.