Effects and causes of different organic materials amendment on soil organic carbon in North China Plain

Abstract: A large number of agricultural organic materials unreasonable is disposed becoming the serious problem of environment pollution produced in China each year. The agricultural organic materials amendment is not only mitigates the environment pollution, but also effectively increases soil carbon sequestration. This study conducted in Wuqiao Experiment Station, China Agricultural University in Hebei province, trying mitigating environmental pollution from agriculture and improving soil carbon sequestration in agriculture system while reduces environmental impacts. Four different types of organic wastes were used in this study with pig manure (PM), biogas residue (BR), biochar (BC) and crop straw (ST). The amount of organic materials is applied by the principles that crop residues returning back to the field based on the yields of wheat and maize yields with 7 500 and 9000 kg/hm2, respectively. Besides, the quantity of C added of BC was equivalent to the total amount of C contained in the crop straw of ST treatment. Whereas, the PM and BR was half of ST, considering the C/N of PM and BR, as well as the situation of the organic fertilizer application of field production. As the principle, 4 treatments were applied for the same amount of nitrogen decided by the highest nitrogen treatment (BR). The shortage of nitrogen of PM, BC and ST were is supplied from inorganic fertilizer which applied with the material before wheat sowing. We compared the effect of organic materials on soil organic carbon (SOC), soil particle organic carbon (POC), soil dissolved organic carbon (DOC) and soil microbial biomass carbon (MBC) in three years, and also analysed the reasons of organic materials amendment on soil carbon sequestration. The present study showed that the SOC in BC, PM and BR treatments were higher than that of ST, respectively, with an average value of 262.4%, 26.8% and 20.7% in the third year. Compared to ST, MBC of BC treatment reduced by 2.9%～35.5% in 2014-2015. DOC in PM and BR treatments were 17.1%～60.1% and 7.2%～64.8% higher than ST. Meanwhile, BC, PM and BR treatments increased 10.8%～148.2%, 9.5%～58.3% and 11.3%～57.6% of POC than ST. Furthermore, there was a significant regression between TOC and POC (R2=0.67，P<0.001), Soil DOC was significantly correlative with MBC (R2=0.52, P<0.001). Biochar improve soil POC accumulation, which would enhance the content and stability of soil organic carbon. Pig manure and biogas residue improved soil labile C (e.g. MBC, DOC and POC), which promote SOC transformation and stability in soil. The effect of biochar pig manure and biogas residue amendment was better than straw returning from the perspective of soil carbon sequestration.