Fertilization enhancing carbon sequestration as carbonate in arid cropland: assessments of long-term experiments in northern China

Soil inorganic carbon (SIC), primarily calcium carbonate, is a major reservoir of carbon in arid lands. This study was designed to test the hypothesis that carbonate might be enhanced in arid cropland, in association with soil fertility improvement via organic amendments. We obtained two sets (65 each) of archived soil samples collected in the early and late 2000's from three long-term experiment sites under wheat-corn cropping with various fertilization treatments in northern China. Soil organic (SOC), SIC and their Stable C-13 compositions were determined over the range 0-100 cm. All sites showed an overall increase of SIC content in soil profiles over time. Particularly, fertilizations led to large SIC accumulation with a range of 101-202 g C m(-2) y(-1) in the 0-100 cm. Accumulation of pedogenic carbonate under fertilization varied from 60 to 179 g C m(-2) y(-1) in the 0-100 cm. Organic amendments significantly enhanced carbonate accumulation, in particular in the subsoil. More carbon was sequestrated in the form of carbonate than as SOC in the arid cropland in northern China. Increasing SOC stock through long-term straw incorporation and manure application in the arid and semi-arid regions also enhanced carbonate accumulation in soil profiles.