Effects of fertilization on wheat yield and soil organic carbon accumulation in rainfed loessial tablelands

Wheat yield and soil organic carbon（SOC）change at the surface layer were investigated by a long-term field experiment with six treatments at the Changwu Ecological Station of the Chinese Academy of Sciences started from 1984 to 2007. The six treatments are fallow (F), control (CK), organic manure (M), nitrogen (N), nitrogen and phosphorus (NP), and nitrogen and phosphorus with organic manure (NPM). The results show that the crop productivity and SOC accumulation are significantly increased under the fertilizer applications. The averaged winter wheat yields of the 23 years are 1.5, 2.6, 2.0, 3.3, and 4.0 t/ha for the CK, M, N, NP, and NPM treatments, respectively. Cumulative amounts of SOC at 0–20 cm soil layer in 2007 are -1.09, 0.76, 8.59, 1.02, 3.42 and 9.5 t/ha for the six treatments. There is a significant correlation between crop yield and SOC content (r=0.80), and moreover, there is a significant correlation between carbon application amount and SOC content (r=0.97), which indicates carbon from farm yard manure plays an important role in improving SOC content. There is a significant difference between the effects of fertilization on carbon sequestration(P0.05) by crop and SOC, and the relationship between soil carbon sequestration rate (Y) and soil organic carbon input (X) can be expressed by a linear equation of Y=0.231X-0.0813 (r=0.98). Fertilization can increase soil productivity and SOC accumulation in the semiarid regions of the Loess Plateau, especially with the combined application of organic and inorganic fertilizer.