Responses of soil carbon, nitrogen, and wheat and maize productivity to 10 years of decreased nitrogen fertilizer under contrasting tillage systems

Excessive nitrogen (N) fertilizer application can cause resource waste and environmental pollution. Thus, whether the rate of N applied can be decreased under no-tillage, which usually increases soil carbon (C) and N stocks, has become an important topic. We hypothesized that a certain extent of N fertilizer application decrease under no-tillage can still maintain higher soil C and N stocks and yields of wheat and maize, however, the effects under different tillage systems may be different. To find the appropriate N fertilizer applications and tillage methods to keep higher soil C and N and crops yields, 10 treatments, including 2 tillage patterns (conventional tillage: CT and no-tillage: NT) and 5 fertilization rates (100%, 75%, 50%, 25% and 0 N of the common N fertilizer application), were tested in triplicate via a randomized block design on a Hapli-Udic Argosol during 2006-2016. The annual wheat and maize yields of 100% N, 75% N and 50% N under CT and NT treatments were significantly higher than those of 25% and 0 N on the studied period (P < 0.05). Higher yield stability of the wheat and maize were found under 75% and 50% N application compared to other N rates. However, the yield stability of wheat was lower than that of maize. The SOC concentration, SOCS and CSR of 75% N application were increased by 1.5, 2.2 and 20.6% than those of 100% N application respectively, in the 0-40 cm soil depth. The STN concentrations of NT-100 and NT-75 were significantly higher than those of other treatments (P < 0.05). The STNS and NSR in the NT-100 treatment were significantly higher than those of other treatments (P < 0.05). NT could lead to more accumulation of SOC and STN in the surface soil depth (0-20 cm) during 2007-2016. In conclusion, 75% of the common N application rate under NT and CT were better choices for sustainable agricultural development.