Changes in soil carbon and nitrogen content, associated with aggregate fractions, after conversion of sandy desert to irrigation farmland, northwest China

Abstract

Soil organic carbon (SOC), soil inorganic carbon (SIC) and silt and clay are the main cementing substances formed by soil aggregates in arid areas. In this study, SOC, SIC and total nitrogen (TN) contents were analysed for different soil aggregate fractions that were reclaimed from different times (5, 15, 20, 35, 40, 50 and 60 years), in northwest China. Our results show that, as cultivation time increased from 0 to 60 years, the number of >2, 2–0.25 and 0.25–0.053 mm aggregates increased from 2.76%, 7.23% and 1.40% to 12.44%, 18.32% and 7.88%, respectively, and the stability of aggregates gradually increased from 0 to 0.43. We also found that the OC in the >2, 2–0.25 and 0.25–0.053 mm aggregates increased from 4.97, 3.81 and 2.63 g kg−2 to 9.45, 7.16 and 4.22 g kg−2, and the TN content increased from 0.70, 0.54 and 0.37 g kg−2 to 1.05, 0.90 and 0.70 g kg−2, while the IC in the >2 mm aggregates decreased from 7.22 to 6.22 g kg−2, and the IC content of the 2–0.25 mm aggregates increased from 5.16 to 7.3 g kg−2. Increasing the silt and clay particle content of soil may be an effective means to achieve continuous improvements in agricultural productivity for newly reclaimed land in the ecologically fragile marginal oasis area.