Stratification of soil organic C, N and C:N ratio as affected by conservation tillage in two maize fields of China

The effects of conservation tillage on profile distributions of soil organic carbon (SOC), total N (TN), and C:N ratios were not well documented in China. The work was conducted at two field experimental sites in the northeast of China. Soils were Cambisols and continuously cultivated with maize (Zea mays L.) for 12 years (Jianping site) and 5 years (Changtu site). Two treatments were conducted at each site and were traditional tillage (TT, i.e., mouldboard plow with residue incorporation) and conservation tillage (CT, i.e., no-tillage with residues left on the soil surface). The responses of SOC and TN stocks to CT differed between the sites and among the soil depths. In the surface soil (0–20 cm), SOC and TN concentrations and C:N ratio were uniformly-distributed under TT. These same response variables decreased with increasing depth under CT. The stratification ratios of SOC for surface to deeper depth (i.e., 0–5 cm:20–40 cm) ranged from 1.5 to 1.8 under CT but only from 1.2 to 1.3 under TT. CT also increased stratification of soil TN and the C:N ratio compared to TT.