Land uses have significant impacts on the changes of land surface covers and ecological processes. Land use type is closely related to the soil fertility and soil carbon pool function. The Ganzhou District and Linze County of Gansu Province, as the typical oasis-desert ecotones, is located in the middle of Heihe River Basin in northwest arid region of China. The topsoil samples were took from the 0-20 cm depth land surface. The topsoil was sampled at Ganzhou District and Linze County during 2011-2012. The soil nutrients were tested in the laboratory including soil organic matter, total nitrogen, total phosphorus, total potassium and pH. We compared the sampled soil nutrients with the national secondary soil survey data in 1980s which have the similar parameters of soil nutrient and pH.
The results showed that the soil organic matter and total phosphorus decreased by 3.54% and 12.5%, respectively, during 2011-2012 in comparison to 1980s. Whereas, the soil total nitrogen, soil total potassium and pH increased by 74.4%, 98.2%, and 4.9%. There had no significant differences of soil nutrients among the desert, cropland and meadow in 1980s. However, the soil nutrients of forest were significantly higher than those of the above three land uses such as soil organic matter, soil total nitrogen and soil total potassium. During the period of 2011-2012, the soil total phosphorus, soil total nitrogen of cropland were significantly different from those of the forest, meadow and desert. The results indicated that the long-term farming activity of cropland reduced soil organic matter by 4.94% and soil total phosphorus by 5.02%, but increased soil total nitrogen by 86.93% and made soil more alkaline. The results also showed that the desert can increase of soil organic matter and soil total nitrogen by 86.93% and 71.70% whereas decrease the soil total phosphorus and soil alkalinity as well. Therefore, the cropland expansion and long-term farming activities can lead to the soil fertility degradation coupling with the risk of salinization. However some natural ecological systems, such as the desert, are favor to improve the soil fertility and soil carbon sequestration.