Profile storage and vertical distribution (0–150 cm) of soil inorganic carbon in croplands in northeast China

Abstract

In addition to soil organic carbon (SOC), soil inorganic carbon (SIC) is also an important reservoir of carbon (C) in arid and semiarid areas, and often contributes a large amount to total soil C. Despite carbonate soils distributed in some regions of northeast China, few data are available on SIC stock, especially in deep soils, resulting underestimation of total soil C. Based on 25 soil profiles (>150 cm) sampled from cropping lands of Lindian County, a typical region of carbonate soils in northeast China, we calculated SIC stock and its distribution in soil profiles and explored their relationship with soil physical and chemical properties. Results showed that SIC density (SICD) within 0–150 cm depth ranged from 109.0 to 331.7 Mg ha−1, with an average of 259.0 Mg ha−1, accounting for 68% of total soil C stock. The ratio of SIC to SOC ranged from 0.1 to 8.0 across soil profiles and was less than 1.0 on average in the upper 40 cm. The SICD in soil profiles were 55.6, 114.4, and 88.9 Mg ha−1 in the 0–40, 40–100, and 100–150 cm, respectively. The stocks of SIC and SOC in the 100–150 cm depth accounted for 23% and 6%, respectively, of the total soil C stock across soil profile. The SIC/SOC ratio was negatively correlated with total nitrogen, available phosphorus and potassium. A structural equation model analysis showed that soil depth combined with soil physical and chemical properties significantly affected the SIC/SOC ratio. Our study highlights the importance of SIC in total C stocks, and indicates SIC stock below 40 cm dominates the total C in soil profile, and SIC stock in deep layers (100–150 cm) can contribute one third to the total stock in the profile (0–150 cm). The distribution of soil C components throughout soil profiles as influenced by soil properties depends on soil layers.