Evolution of Soil Structure and Fertility After Conversion of Native Sandy Desert Soil to Irrigated Cropland in Arid Region, China

Abstract

Assessment of soil quality and its direction of change with time is a primary indicator of sustainable agricultural land management. In this study, the temporal changes in soil physical and chemical properties were determined after conversion of native desert soils to irrigated croplands in a marginal oasis of the arid region, northwest China. Soil samples were collected from seven closely located farm fields that had been cultivated for 3, 5, 10, 14, 23, 30, and 40 years after agricultural cultivation, from adjacent remnant uncultivated sandy land (0 year), and from farm fields in an old oasis cultivated for more than 50 years. All the soils in the study were Psamments that derived from the deposition of aeolian sand. After cultivation, significant changes in particle size distribution and aggregate size distribution and stability in the 0- to 20-cm surface soil only occurred in soils cultivated for more than 10 years, showing a consistently increasing pattern with increasing duration of cultivation. The result indicated that soil did not contain enough coarse aggregates to control wind erosion, suggesting the need to maintain residues on the soil surface to aid wind erosion control for these newly cultivated sandy soils. As cultivation time increased, soil organic carbon (SOC), total and available N and P, cation exchange capacity, and CaCO3 concentrations all increased. Soil organic carbon and total N concentrations increased by 6.4 times and 5.9 times, respectively, after 40 years of continuous cropping. The increased silt and clay content caused by irrigation with silt-laden river water plays an important role in the aggregate formation and SOC and nutrient accumulation and retention. The results also indicated that the evolution of desert soil toward the sustainable agricultural soil requires at least 50 years. The absolute amounts of soil aggregate, SOC, and nutrients are still low after 40 years of cropping and were insufficient to support sustaining crop production. Therefore, improved land management such as conservation tillage and crop and grass rotation is imperative to accelerate soil structure and fertility improvement and maintain long-term productivity of the farmlands.