Ageing Effect Of Biochar On Soil Nutrients And Growth Of Rice

Biochar plays a positive role in improving crop yield and promoting low-carbon and sustainable development, due to good physical and chemical properties. However, the stable properties of biochar also possess some instability. After applying to the soil, its physical and chemical properties also have slight change overtime, which is ageing. Aging might have an effect on soil quality and crop yield. In order to elucidate the aging possess of biochar, analyze its mechanism and effects on crop growth, the experiment with three treatments including biochar, biochar with soil, and soil were performed. Two approaches of accelerating aging process, including freeing-thrawing cycle and dry-wet cycling, were conducted to simulate the changing process of the physical and chemical properties of biochar and explore the roles of biochar in the changes of the soil nutrition. Experiments on cold tolerant rice seedlings with high-selection pressure were conducted as a method to examine the influence of ageing biochar on plant growth. The results of this study provide us with a basis and reference for a proper application of biochar in agricultural production. Main results are as follows:1. Biochar, especially rice husk biochar, is better to retain the morphology and cell chamber structure of raw material. Compared with the raw material, some characteristics of biochar are significantly improved including carbon content, silicon content, ash content, fixed carbon content, specific surface area, vtotal and pore size. While the volatile content of biochar is significantly lower than the raw material’s. Surface structure analysis concluded that the specific surface area of biochar was100times and the total pore volume was about10times higher than that of raw material’s. These indicated that biochar had large surface area, or rich pore structure.2. Aging treatment has a significant impact on the physical and chemical properties of biochar. The surface structure, pH values, element composition, oxidation of the surface, absorption capacity of biochar changed in the ageing process. In the simulation test of freeze-thaw cycles, pH of biochar displayed upward trend after the first decline in25cycles, and then return to the initial level, indicating that the pH of biochar is not easy to change. Reason for this phenomenon is concerned with carbonate content and functional groups of biochar. Freeze-thaw cycle processes have a greater impact on the surface properties of biochar. Biochar surface oxidation occurs rapidly and significantly in the early, and then stabilized in the latter stage. Surface oxidation degree is higher than the whole. In the first11cycles, oxide is about2times higher than that of the overall oxidation. The results showed that surface oxide of biochar protect the internal particles from further oxidation. In the first25freeze-thaw cycles, adsorption capacity of biochar to hydroquinone changes from the5.928mg.g-1to11.73mg.g-1, indicating that freeze-thaw cycle treatment increase adsorption capacity of biochar. In alternating wet and dry cycle simulation study, the pH of biochar reduce gradually. The change of the element is less than that in the freeze-thaw cycle treatment. The change of adsorption isn’t significant. Overall, the different treatment significantly affects the aging process of biochar, the effect of alternating wet and dry treatment on biochar ageing is less than that of the freeze-thaw cycle.3. It was showed that exogenous application of biochar could effectively reduce the loss of nitrogen in soil leaching solution and affected the C/N ratio in soil. In the freezing and thawing cycle conditions, the amplitude of C/N ratio was B>M>S. We speculated that application of biochar could affect the activities of microorganism in soil and the C/N ratio. Additionally, we also found that in the freezing/thawing cycle and leaching conditions, the content of potassium reduced drastically. The possible reason may be that the content of potassium in biochar was much higher, more than10-30times, than that in soil.4. Ageing biochar has a great impact on rice growth. It could reduce the contents of chlorophyll and carotenoids in rice seedling significantly. Under chilling stress, ageing cycles have different effect on physiological properties of rice seedlings. Total chlorophyll and carotenoid contents in the5cycles were significantly higher than that at other cycles. The exosmosis conductivity in the15cycles were significantly lower than that at other cycles. The expression of protein biosynthesis genes of GAs in the11and20cycles were significantly lower than that of other cycles.