Synthesis And Properties Of Slow-release Nitrogen Fertilizer Based On Carbon Spheres

Nitrogen nutrient loss and non-point source pollution are serious in farmland in China,and more and more attention has been paid to the environment friendly and resource-saving new fertilizers.The most common slow-release fertilizer in modern agricultural production is coated fertilizer,but the coated material is not easy to degrade,and successive years of application will cause pollution to the soil.There is an urgent need for an environmentally friendly fertilizer.Therefore,this study used cheap glucose as raw material to synthesize carbon spheres（CSs）by hydrothermal method,which was applied to fertilizer carrier.And urea and CSs were compounded to prepare a new type of carbon-based slow-release nitrogen fertilizer by direct mixing method,water-soluble soaking adsorption method,hydrothermal method and co-pyrolysis method.The fertilizers synthesized by direct mixing,aqueous soaking and adsorption and hydrothermal method were denoted as SRF-S,SRF-M and SRF-H,respectively.The fertilizers prepared by co-pyrolysis were denoted as SRF-P₁₁₀,SRF-P₁₄₀ and SRF-P₁₇₀,respectively.Scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FTIR）and thermogravimetry（TG）were used to characterize CSs and carbon-based slow-release nitrogen fertilizer to explore their surface morphology and structure.In order to explore the sustained release performance of each fertilizer,hydrostatic leaching and soil column leaching tests were designed in this study.The data were fitted by dynamic model to reveal the mechanism of sustained release.In order to verify the slow-release performance of each fertilizer,we designed two seasons crops of Pakchoi pot experiment to explore its effect on crop growth.The main results are as follows:（1）The results of SEM,FTIR and thermogravimetric characterization of CSs showed that its surface morphology was regular and orderly,its surface functional groups were abundant,and it showed good thermal stability.And it was a good fertilizer carrier.Elemental analysis of the above six fertilizers showed that the nitrogen content of SRF-M was the highest,19.66%.The p H values of six fertilizers were measured and found to be concentrated between 6.15 and 6.64,which can be used as an alkaline soil improver.FTIR results showed that nitrogen in urea was successfully loaded into CSs matrix.Thermogravimetric analysis results showed that SRF-H had the strongest thermal stability.（2）Leaching test results showed that the general trend of nitrogen release rate curve of each fertilizer in water was similar to that in soil,but the total nitrogen release amount of each fertilizer in water was larger than that in soil.Kinetic model fitting showed that nitrogen release from fertilizer in water was more consistent with first-order kinetic model.The release rate of nitrogen in water depended on the concentration of nitrogen.The release of nitrogen from fertilizer in soil was more consistent with Korsmeyer-Peppas dynamics model,and the release of nitrogen in soil followed Fickian diffusion mechanism.In soil column leaching test,the order of nitrogen release rate was U>SRF-S>SRF-M>SRF-P₁₁₀>SRF-P₁₄₀>SRF-P₁₇₀>SRF-H.Within the first 42 days,the cumulative nitrogen release of SRF-M,SRF-S and SRF-P₁₁₀ was 55.78,62.98 and 42.16%,respectively,which were 34.50,27.30and 48.10%lower than that of U,respectively.Therefore,it can be concluded that SRF-M and SRF-S showed excellent slow-release performance,and SRF-P₁₁₀ was the second.SRF-H and SRF-P₁₇₀ were not suitable as slow-release fertilizers due to their total release amounts less than 9%within 42 days.（3）In view of the excellent slow-release properties of SRF-M,SRF-S and SRF-P₁₁₀,we further designed pakchoi pot experiments to explore their effects on crop growth.The results of pot experiment showed that the fresh weight of aboveground part of pakchoi under SRF-M treatment was the highest in the first crop of pakchoi compared with urea treatment group,and the nitrogen use efficiency was improved.Compared with the U treatment group,in SRF-P110 group the contents of soluble sugar and vitamin C were significantly increased,and the contents of nitrate were significantly decreased.The quality of pakchoi has improved significantly.Therefore,SRF-M was suitable for crops with short growth cycle（0-50 d）and can significantly improve the yield of pakchoi.The carbon-based slow-release fertilizer(SRF-P₁₁₀)prepared by co-pyrolysis can greatly improve the quality of pakchoi.In summary,in this study,glucose was used as raw material to prepare CSs.And carbon based slow-release nitrogen fertilizer was prepared by direct mixing method,aqueous immersion adsorption method,hydrothermal method and co-pyrolysis method.Among them,the carbon-based fertilizer prepared by direct mixing method has the best slow-release performance,and can significantly improve the yield and quality of pakchoi compared with the quick-effective nitrogen fertilizer.In addition,the direct mixing method is simple and consumes less energy,which is expected to be a kind of slow release nitrogen fertilizer in agricultural production.