Effects of silicate rock weathering and agricultural cultivation on carbon sequestration in saline soils: an example from the saline soils of Bayannur, Northwest China

Carbon sequestration in arid areas is a crucial component of the carbon cycle in terrestrial ecosystems. As an alluvial plain in the upper reaches of the yellow river, saline soils in Bayannur have a huge capacity for carbon sequestration. Weathering of coarse-grained silicate minerals (feldspar) from the Langshan Mountain generate CO32− or HCO3−, which combine with Ca2+ transported by the Yellow River, forming inorganic carbon sequestration. Additionally, humic substances produced by agricultural activities, alongside microbial residues, contribute to organic carbon sequestration. This research examines the processes and influencing factors of organic and inorganic carbon sequestration in arid regions by analyzing the soluble salts, minerals, elements, and dissolved organic matter (DOM) in the topsoil of Bayannur. The results showed that the topsoil (0–10 cm) was highly alkaline, with pH levels ranging from 8.07 to 9.94. The dominant soluble salts in the soil were Na+ and SO42−. Soil minerals content in descending order was quartz (Qtz), clay minerals (Clay), plagioclase (Pl), calcite (Cal), K-feldspar (Kfs), and dolomite (Dol). The soil organic carbon (SOC) content ranged from 0.16 to 0.89%, while the soil inorganic carbon (SIC) content ranged from 0.93 to 1.86%. The SOC content in the topsoil of Bayannur (cultivated saline soils) surpasses that in natural saline soils (uncultivated), likely due to increased carbon input from crops and agricultural fertilization. Similarly, the SIC content is also higher than that in natural saline soils. This is attributed to the irrigation process, which increases the concentration of Ca2+ in the soil and accelerates the weathering of the topsoil.