引用本文:姜 宇,刘 博,范昊明,马仁明.冻融条件下黑土大孔隙结构特征研究[J].土壤学报,2019,56(2):340-349.
Jiang Yu,Liu Bo,Fan Haoming,Ma Renming.Macropore Structure Characteristics of Black Soil under Freeze-Thaw Condition[J].Acta Pedologica Sinica,2019,56(2):340-349
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冻融条件下黑土大孔隙结构特征研究
姜 宇, 刘 博, 范昊明, 马仁明
沈阳农业大学水利学院
摘要:
冻融作用会改变土壤微观结构,孔隙特征的变化是其结构性改变的重要体现。研究冻融作用对开展黑土区侵蚀机理研究及合理利用黑土资源具有重要意义。本研究旨在对冻融条件下原状土样的三维结构进行分析,获取孔隙特征的定量指标,进而分析冻融循环对土壤大孔隙的影响,为进一步揭示黑土区季节性冻融对黑土结构的影响提供证据。通过室内冻融循环试验结合CT扫描技术研究黑土原状土体大孔隙在7种冻融循环次数以及两组含水率下的变化规律,探讨在冻融循环作用下原状土体大于1.25 mm的孔隙变化特征。结果表明:在15次冻融循环内,随着冻融循环次数的增多,土壤孔隙度不断增大,在7次冻融循环后增长尤为显著;孔隙数量随冻融循环次数的增多而减小;规则孔隙度(RP)持续减小,不规则孔隙度(IRP)呈减小趋势而加长孔隙度(EP)呈增大趋势;孔径随冻融循环次数的增多而增大,孔径大于3 mm的孔隙孔隙度不断增大;冻融作用使孔隙出现大量分支,冻融循环次数越多分支占比越大。在冻融温差一定时,冻融循环后高含水率土壤比低含水率土壤的上述孔隙特征变化更为显著。研究成果为阐明冻融侵蚀机理、合理评价及利用寒区农田提供理论依据。
关键词:  冻融循环  黑土  原状土  CT  大孔隙
DOI:10.11766/trxb201805230516
分类号:
基金项目:国家自然科学基金项目(41601284)、国家重点研发计划项目(2016YFE0202900)和辽宁省教育厅科学研究项目(LSNYB201610)
Macropore Structure Characteristics of Black Soil under Freeze-Thaw Condition
Jiang Yu, Liu Bo, Fan Haoming, Ma Renming
College of Water Conservancy, Shenyang Agricultural University
Abstract:
【Objective】 Freeze-thaw action will change the microstructure of a soil, and the change in pore characteristics is an important reflection of the change in soil structure. Most of the regions along the mid-latitudes on earth are affected by seasonal freeze-thaw processes, especially the black soil in Northeast China. It is of great significance to study mechanism of the erosion on black soil and rational utilization of the black soil resources. So this study is oriented to analyze three-dimensional structure of the soil under freeze-thaw condition, extract quantitative indices of pore characteristics, and then explore effects of freeze-thaw cycle on soil macropores, in an attempt to provide evidence for further revealing influences of seasonal freezing and thawing on soil structure of the black soil area. 【Method】 In this paper, through indoor simulation experiment of freeze-thaw cycle and with the aid of the CT scanning technique, changes in macropore in the undisturbed black soil samples under different numbers of freeze-thaw cycles and different moisture contents were studied. Undisturbed soil samples, 0~15 cm in depth, were collected with PVC pipe from a typical black soil area for the indoor simulation experiment of freeze-thaw cycle, which was designed to have two moisture contents (30% and 40%), and seven levels of freeze-thaw cycles (0, 1, 3, 5, 7, 10 and 15), each ranging in temperature from -10 to 7°C. With the aid of a medical CT, 1.25 mm in resolution, changes in pores > 1.25 mm in pore size were studied. 【Result】 Results show that with the increasing number of freeze-thaw cycles, soil porosity continuously increased, especially after the 7th freeze-thaw cycles, while the number of pores decreases; regular porosity (RP) and irregular porosity (IRP) continued to decrease, but lengthening porosity (EP) increased; and pore size increased, especially that of those >3 mm in diameter. Besides, freeze-thaw action caused formation of a lot of branches along pores, and the more the numbers of freeze-thaw cycles, the higher the proportion of branches. Among the soil samples subjected to the same temperature variation in freeze-thaw cycles, those high in soil moisture content changed more significantly in pore characteristics than those low in soil moisture content. 【Conclusion】 As affected by freeze-thaw cycle, soil porosity, pore size and pore branching increased, and soil pores changed significantly in shape and distribution. All the findings in this study show that the number of freeze-thaw cycles and soil moisture content are the two major factors affecting pore structure of the soil. Properties of the soils under freeze-thaw cycle is not only a very important research hotspot, but also a major factor concerning sustainable development of the agriculture in Northeast China. In order to reveal mechanism of freeze-thaw erosion of the soil, further study should be done focusing on pore structure characteristics of aggregates and relationships between pore structure characteristics and soil water-holding and infiltration characteristics in the soil under freeze-thaw cycle. The study may provide a theoretical basis for researches on mechanism of freeze-thaw erosion of soil and reasonable evaluation and utilization of farmlands in cold-temperate areas.
Key words:  Freeze-thaw cycle  Black soil  Undisturbed soil  CT  Macropore