中国北方农牧交错带鄂尔多斯高原段土壤表层粒度特征

Characteristics of Soil Surface Grain Size in Ordos Plateau along the Agro-pastoral Ecotone of North China

土壤粒度是描述土壤性质的重要参数,研究农牧交错带土壤表层粒度对土壤质量和沙化程度评价具有科学意义。对不同沉积物类型及土地利用方式土壤表层(0~5 cm深度)粒度进行分析。结果表明:(1)沙黄土、覆沙黄土残积物、风化残积物中粉粒最多,其次为极细砂和细砂,这3个粒级含量之和表现为沙黄土(96.51%)>覆沙黄土残积物(88.29%)>风化残积物(77.58%);风成沙土壤表层以细砂(53.85%)和中砂(26.13%)为主。(2)平均粒径由小到大依次为沙黄土(4.78Φ)、覆沙黄土残积物(4.62Φ)、风化残积物(3.80Φ)、风成沙(2.46Φ);分选性由差到好依次为风化残积物、覆沙黄土残积物、沙黄土、风成沙;偏度呈现为正偏或极正偏;峰值表明风成沙(2.30)粒径分布最为集中。(3)同一地表沉积物中,砾石和极粗砂等粗颗粒在农田较多,粉粒在草地较多,极细砂在林地较多;风成沙中,粉粒在固定沙丘略多,细砂在半固定沙丘较多,砾石、极粗砂等粗颗粒仅在流动沙丘地中分布。(4)土壤颗粒分形维数表现为沙黄土(2.5242)>覆沙黄土残积物(2.4373)>风化残积物(2.3554)>风成沙(2.2815);地表沉积物类型不同,表层土壤分形维数与粒级含量相关性有着明显差异。

The study of soil surface grain size in the agro-pastoral ecotone is of scientific significance to the evaluation of soil quality and the desertification degree. Through the soil surface samples analysis in the study area, we discussed the grain size characteristics of different types of sediments and different land use types. The results showed that:(1)Sand loess, sand covered loess residues and weathering residues have the highest silt content, followed by very fine sand and fine sand. The sum of the contents of the three grain grades is shown as sand loess(96.51%)>sand covered loess residues(88.29%)>weathering residues(77.58%). The surface soil grain components of aeolian sand are mainly fine sand(53.85%) and middle sand(26.13%).(2)Soil grain size parameter results show that the average grain size from fine to coarse is sand loess 4.78Φ, sand covered loess residue 4.62Φ, weathering residue 3.80Φ, and aeolian sand 2.46Φ;the order of sorting coefficient is weathering residual, sand covered loess, sand loess, and aeolian sand;the degree of skewness is positive or very positive;the kurtosis value shows that the grain size distribution of aeolian sand(2.30) is the most concentrated.(3) In the same surface sediment, there are more coarse grains such as gravel and very coarse sand in farmland, more silt in grassland and more fine sand in woodland. In the aeolian sand, there are a little more fixed sand dunes with powder content, more semi-fixed sand dunes with fine sand content, and only coarse grains such as gravel and very coarse sand distributed in the mobile sand dunes.There were more coarse grains(0.56%-9.82%) such as gravel and very coarse sand in farmland, more silt(38.65%-60.33%) in grassland, and more very fine sand(22.46%-39.93%) in forest land. Fixed dunes have the more silt content(12.76%), and semi-fixed dunes have the most fine sand content(57.73%);the coarse particles, such as gravel and very coarse sand, are distributed only in the moving sand dunes(3.12%).(4)The fractal dimension of soil grain is as follows: sand loess(2.5242)>sand covered loess residues(2.4373)>weathering residues(2.3554)>aeolian sand(2.2815). The correlation between the fractal dimension of surface soil and grain content was significance different from that of surface sediment.