| Biochar (BC) refers to the highly aromatic substance remaining after pyrolysis of biomass under complete or partial exclusion of oxygen. Its application has been suggested as an effective measure of abating climate change by sequestering carbon. BC not only is the source of soil humic substances, but also can improve soil structure and soil fertility. But it should take some time to work with soil to achieve a relatively stable state because biochar application rate is usually higher. Therefore, a3-year field experiment was conducted to investigate the effect of biochar on soil organic carbon (SOC) cycling. BC was applied as a basal soil amendment in2009at the rate of0,10,20and40t hm-2and in2012(the third year after BC application), the aggregates of soil were obtained using physical dispersion procedure and13C-NMR analytic technique, and soil organic carbon, humin fractions and soil aggregates were studied to provide the basis for carbon sequestration and green house gases mitigation.The main findings were as follows:1) BC has persistent effects on soil total organic carbon (TOC) and its fractions. BC application significantly increased SOC storage by9.15%～15.49%, and TOC, readily oxidation carbon (ROC), particulate organic carbon (POC) and microbial biomass carbon (MBC) were also increased by12.75%～23.36%,12.60%～28.00%,10.88%～34.00%and7.97%～12.35%, respectively by BC application. The results suggested biochar-sourced organic carbon could be steadily maintained in soils (3years at least), which was related to the capabilities of BC to improve soil structure and promote crop growth. TOC was very significantly correlated with ROC and MBC, while there was a very significant correlation among ROC, POC and MBC. Thus, BC application is a continuous effective measurement to improve organic carbon storage and the contents of soil active organic carbon of paddy soil.2) The effects on soil humin structure by BC were based on different humin fractions. The HA-C content and its alkylate significantly decreased by1.06%～1.48%and1.92%～2.10%, respectively, while HM-C content significantly increased by11.63%～46.67%after adding biochar to soil. Wheat straw BC and its HM had the same structure (aromatic C), Further illustrating that HM-C increased because BC application on soil organic carbon increased mainly in the increase of HM-C. HM in soil had more complex molecule structure and enhanced Hydrophobic by BC to benefit for soil organic carbon and aggregate stability;3) BC was beneficial to stability of soil aggregates. The content of organic carbon in aggregates were higher in the200～20μm and lower in the<2μm. BC treatments significantly increased the rative contents of2000～200μm by6.54%～12.93%, respectively. And significantly decreased the rative contents of20～2μm and<2μm by1.84%～6.54%and1.00%～2.28%, respectively. The particle organic carbon and total nitrogen distribution. The SOC and TN of soil aggregates were distributed consistent, mainly in2000～200μm and <2μm fractions. The BC treatments of20and40t hm-2significantly increased SOC concentration by11.01%～18.75%,35.62%～56.86%and38.96%～40.08%respectively in the2000～200μm,20～2μm and<2μm fractions. And BC treatments significantly increased TN contents by13.54%～23.44%and11.31%～54.96%, respectively. SOC were mainly stored in2000～20μm fractions, and the storages of SOC were increased in2000～200μm but decreased in<2μm fractions with BC application. Therefore, BC plays an important role in soil structure and increases the storage of SOC in rice paddy soil. |
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