| A large number of agricultural residues, such as crop straw, poulty excrement and municipal wastes are produced during agricultural activities in China. They will cause serious pollutions into environment as well as resouces waste, if not used properly. It is vital to solve the problem of resource utilization of agricultural residues for sustainable development in China’s agriculture. The conversion of biomass to biochar through pyrolysis under limited O2 condition opens a new way for resource utilization of agricultural residues and it has been widely noticed and studied in recent years. Biochar has a great potential not only to sequestrate carbon and mitigate greenhouse gases (GHGs) emission from soils, but to improve soil properties and nutrition use efficiency, thus enhance crop yields. Moreover, the implement of using biochar as a fertilizer carrier to make biochar compound fertilizer (BCF) can solve the financial cost problem when applied biochar as a soil amendment in large amount. The combination between biochar and conventional chemical fertilizer (CCF) also can significantly improve fertilization use efficiency, which is able to cope with a series of environmental pollution problems caused by low use efficiency of chemical fertilizers.In this study, BCFs were manufactured through combining biochars derived from different bio-wastes and CCF together to make them granular before applying into paddy lands. Then the effects of these BCFs on plant nutrition utilization, GHGs emission from soil and rice yield were investigated. Afterwards, an modification research on previous manufacture craftsmanship was conducted to make two new BCFs, and then their respective surface structure and chemical properties were analyzed before a pot trial with pakchoi planted, in which a CCF and an original rice husk BCF were as comparison to test whether these two new BCFs can have a better performance on plant (pakchoi, Brassica chinensis L.) growth or not. Main results were as follows:(1) Results for field experiment indicated BCFs could slow release ammonia in surface water during former flooding period and reduce nitrate content during latter flooding period as compared with CCF treatment, indicating that nitrogen transformation in surface water was influenced by the application of BCFs and they equipped ability to supply N for a long time. Besides, BCF treatments could reduce total CH4 and N2O emissions from paddies during the whole rice growing season (WRGS) respectively by 25.5～50.6% and 31.0～39.4% over CCF treatment, while no significant difference was observed as for CO2 emissions among treatments. Moreover, BCFs also significantly cut down 29.8～42.9% and 36.4～56.5% as compared with CCF treatment in terms respectively of global warming potential (GWP) for CH4 and N2O under 100 years scale and greenhouse gas intensity (GHGI), which indicated BCFs’great mitigation potential. As to the rice yield, BCF treatments ensured rice grain yield in spite of reducing 20% N application rates as compared with CCF treatment. Peanut husk BCF (PH-BCF) and municipal wastes BCF (MW-BCF) treatment even significantly increased yield by 28.1% and 31.4% over CCF. Besides, BCF treatments improved nitrogen partial factor productivity (NPFP) by 28.1%～63.2% over control, significantly enhancing the N use efficiency.(2) New BCFs were produced by modifying previous manufacture craftsmanship and their respective surface structure and chemical properties were analyzed to show a great deal of sub-micro and nano mineral phases existed around the surface of new BCFs, which were made through converting mixtures of different kinds of clay minerals and activated biomass into biochar before chemical reactions with different nutrients. X-ray photoelectron spectroscopy (XPS) and scanning electron miscroscope (SEM) analysis showed there was a majority of organic functional groups, oxides and different kinds of mineral phases on BCFs’surface, which could contribute to plant growth. And also nutrients distributed evenly on their surface. The Energy Dispersive Spectroscopy (EDS) map displayed a good doublication between C and N, suggesting a possible N slow-release ability.(3) Results for pot trial of new BCFs manifested three BCFs could stimulate pakchoi growth, improve qualities and nutrient use efficiency at different extents as compared with CCF. As to the growth condition of pakchoi, the bentonite pelleted new BCF (BN-BCF) had similar effects with RH-BCF, and better than kaolin pelleted new BCF (KN-BCF). Besides, BN-BCF had a better influence on pakchoi qualities than other two BCFs, significantly decreasing nitrate content by 19% and increased soluble sugar, Vitamin C and chlorophyll content respectively by 35%,22% and 6% as compared with CCF. While to the nutrient utilization, all BCFs significantly stimulated nutrition uptakes by pakchoi over CCF, in which two new BCFs significantly increased the P uptakes by pakchoi as compared with RH-BCF. And to the total fertilization PFP, BN-BCF was also better than other BCFs. Comparatively, the BN-BCF had a better performance in the pakchoi growth, qualities improvement and nutrient utilization as compared with other BCFs.Overall, BCFs manufactured by combining biochars pyrolyzed from different bio-wastes and regular chemical fertilizer together could not only slow release nitrogen in surface water during former flooding period, so to supply N for a long time, but also reduce the GHGs emission from paddies, which indicated their great mitigation potential. Besides, BCFs could ensure or even significantly increase rice yield on the condition of decreasing N input as compared with CCF, improving the N use efficiency dramatically. Furthermore, the modification research on BCF suggested the increase of sub-micro or nano mineral phases and organic functional groups on BCFs’surfaces could further stimulate nutrient utilization efficiency, and have a positive effect on vegetable growth and qualities. From what we’ve found above, it is necessary to go further on the research of BCFs, which will definitely contribute to their future popularization and application, also to the development of our low-carbon and sustainable agriculture. |
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