Soil Properties and Characteristics of Soil Aggregate in Marginal Farmlands of Oasis in the Middle o

The composition and stability of soil aggregate are closely related to soil quality, soil erosion, and agricultural sustainability. In this study, 49 soil samples at the 0-10 cm surface layer were collected from four soil types (i.e., Ari-Sandic Primosols, Calci-Orthic Aridosols, Siltigi-Otrthic Anthrosols, and Ustic Cambosols) in the marginal farmland in the oasis of the middle Hexi Corridor region and was used to determine the characteristics of soil aggregates. The composition of dry- and wet- sieved aggregates and the physical and chemical properties (including soil particle distribution, soil organic carbon (SOC), calcium carbonate (CaCO3), and oxides of Fe3+ and Al3+) of the selected soils were analyzed. The results show that soil particle size distribution is dominated by fine sand fraction in most of soils except Ustic Cambosols. Soil organic carbon concentration is 5.88 ± 2.52 g kg-1 on average, ranging from 4.75 g kg-1 in Ari-Sandic Primosols to 10.51 g kg-1 in Ustic Cambosols. The soils have high calcium carbonate (CaCO3) concentration, ranging from 84.7 to 164.8 g kg-1, which is increased 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, and large dry blocky aggregates (> 5 mm) is dominant in all soils. The mean weight diameter of dry aggregates (DMWD) ranges from 3.2 mm to 5.5 mm. The percentage of > 0.25 mm water-stable aggregate is from 23.8% to 45.4%. The percentage of aggregate destruction (PAD) is from 52.4% to 66.8%, which shows a weak aggregate stability. Ari-Sandic Primosols has the highest PAD. The distribution and characteristics of soil aggregates are in favor of controlling soil wind erosion. However, the stability of aggregate of all soils is weak and soils are prone to disperse and harden after irrigation. The mass of macro-aggregates and DMWD are positively significantly correlated with the contents of soil clay and silt, so