Dynamics of crop yields and soil organic carbon in a long-term fertilization experiment in the Huang-Huai-Hai Plain of China

We analyzed the dynamics of crop yields and soil organic carbon content (SOC) in a long-term fertilization experiment carried out in the Huang-Huai-Hai Plain of China. The experiment with crop rotation of winter wheat and summer maize started in 1990 and had seven treatments receiving N, P, and K at the same rates if it was applied. The treatments were inorganic fertilization (NPK, NP, PK, NK), organic fertilization (ON), half amount of N from inorganic fertilizer and another half from compost (1/2ON), and no fertilization as control (CK). On average, over 14 years (1990–2003), both wheat and maize yields were the highest and most stable in the NPK treatment. Average wheat and maize yields were 23.7% and 18.0% lower in ON, respectively, and slightly but significantly lower (1.9% and 1.5%, respectively) in 1/2ON than those in NPK. Unbalanced inorganic fertilization without K (NP) was not sustainable for achieving high yields. There was a significant logarithmic relationship between roots and compost input and SOC content in 0–20 cm in 2003. Over the time of the study SOC storage in 0–20 cm increased by 12.2 Mg C ha− 1 in ON, 7.8 Mg C ha− 1 in 1/2ON, and 3.7 Mg C ha− 1 in NPK, and decreased by 1.6 Mg C ha− 1 in NK and 1.4 Mg C ha− 1 in CK. Measured dynamics of SOC and model simulation predictions showed that the SOC in NPK, ON and 1/2ON almost reached equilibrium in 2003. These results indicate that although the balanced application of chemical fertilizers of N, P, and K maintains the crop production in the region, it is not an ideal practice from the point view of carbon sequestration in soil. Application of compost alone has a reverse effect on crop yields and carbon sequestration in soil. Therefore, mixed application of organic and inorganic fertilizers is a compromise between food security and soil carbon sequestration in the region.