Soil properties and soil aggregate characteristics in marginal farmlands of oasis in middle Hexi Corridor region

Chino. 土壤团聚体组成及其稳定性与土壤质量、土壤侵蚀和农业可持续性有着密切联系。在甘肃河西走廊中段近几十年来开垦的边缘绿洲区4种土类中（砂质新成土、正常干旱土、旱耕人为土和干润雏形土）采集49个农田表层土样（0～10 cm），用干筛和湿筛法分析土壤团聚体组成及其稳定性，并分析了与土壤团聚体形成有关的土壤物理、化学性状。除干润雏形土外，大部分土壤粒级组成以沙粒为主；土壤有机碳含量低，平均为（5.88±2.52）gand#8226;kg-1，4种土类中有机碳平均含量平均为4.75～10.51 gand#8226;kg-1，以砂质新成土最低，干润雏形土最高；碳酸钙含量普遍较高，平均含量为84.7～164.8 gand#8226;kg-1，随土壤粘粉粒和有机碳含量的增加而增加；不同土类＞0.25 mm的干团聚体平均变动在65.2%～94.6%，干团聚体组成以5 mm的大块状团聚体（土块）为主，平均重量粒径（DMWD）变动在3.2～5.5 mm；0.25 mm的水稳性团聚体变动在23.8%～45.4%，团聚体破坏率（PAD）为52.4%～66.8%，团聚体组成和特征有利于抵抗土壤风蚀，但稳定性差，灌溉后易于分散、沉实板结、通透性差。土壤粘粉粒、有机碳、碳酸钙及铁铝氧化物均对团聚体的形成有显著作用，以土壤粘粒和细粉粒作用最大，有机碳和碳酸钙作用次之；但有机碳和碳酸钙对团聚体的稳定性较粘粉粒的影响更为明显。退耕种植多年生苜蓿后，土壤有机碳、团聚体数量及其稳定性显著增加。对生态脆弱的边缘绿洲区新垦土地，退耕还草或推行草粮轮作，是改善土壤结构、提高土壤肥力、减轻土壤风蚀的可持续土地利用的有效途径。

Inglés. Soil aggregate composition and stability are closely related to soil quality, soil erosion and agricultural sustainability. In this study, 49 soil samples at 0-10cm surface layer were collected from four soil types (i.e. Ari-Sandic Primosols, Calci-Orthic Aridosols, Siltigi-Otrthic Anthrosols and Ustic Cambosols) in marginal farmlands of oasis in middle Hexi Corridor region to determine the characteristics of soil aggregates. The composition of dry-sieved and wet sieved aggregates and some selected soil physiochemical properties including soil particle distribution, soil organic carbon, calcium carbonate（CaCO3）and oxides of Fe3+ and Al3+ were determined. Results show that soil particle size distribution is dominant in fine sand fraction in most of soil types with exception of Ustic Cambosols. Soil organic carbon concentration is (5.88±2.52)gand#8226;kg-1 on average, and ranges from 4.75 gand#8226;kg-1 in Ari-Sandic Primosols to 10.51 gand#8226;kg-1 in Ustic Cambosols. There is a high Calcium carbonate（CaCO3）concentration in the soils and ranges from 84.7 g kg-1 in Ari-Sandic Primosols to 164.8 gand#8226;kg-1 in Ustic Cambosols, indicating an increasement with soil fine particle and organic carbon content. The percentage of 0.25 mm dry aggregates ranges from 65.2% in Ari-Sandic Primosols to 94.6% in Ustic Cambosols, while large dry aggregates (5 mm) are dominant in all soils. Mean weight diameter of dry aggregates (DMWD) ranges from 3.2 mm to5.5 mm. Mass of 0.25 mm water-stable aggregate is 23.8%-45.4%. Percentage of aggregate destruction (PAD) ranges from 52.4% to 66.8%, showing a poor aggregate stability. Ari-Sandic Primosols have the highest PAD. Better distribution and characteristics of soil aggregates are favorable for controlling soil erosion caused by wind. However, the stability of aggregate for all soils is low and soils are prone to disperse and harden after irrigation. The mass of macro-aggregates and DMWD are positively correlated with the content of soil clay and silt, soil organic carbon (SOC), CaCO3, and oxides of Fe3+ and Al3+. Soil fine silt and clay, SOC and CaCO3 are important factors of aggregation in this region. Effects of SOC and CaCO3 on aggregate stability are more significant than that of soil silt and clay. Converting cropland to alfalfa forage land can increase SOC concentration, and in turn, enhance the formation of aggregates and stability. For the marginal farmlands in this fragile ecological area, returning cropland to alfalfa grassland or performing crop-grass rotation is an effective and basic strategy to improve soil structure and quality, mitigate soil erosion by wind and to enhance oasis agricultural sustainability.