Manufacture Of Nano-SiO₂-polyvinyl Alcohol-?-glutamic Acid Composite Coated Fertilizer And Its Nutrient Slow And Release Mechanism

Polyvinyl alcohol?PVA?,as a coating material of slow-released fertilizer,has advantages of low price and friendly to environment.However,the water resistance of PVA film is poor.The slow-released effectiveness of fertilizer coated with the PVA does not last long in soil.The particle size of nano-silicon dioxide?Nano-SiO₂?is small,and Nano-SiO₂ addition could improve the water resistance of membrane materials.?-polyglutamic acid??-PGA?is a kind of environmental-friendly fertilizer synergist.In theory,the PVA properties could be modified by adding Nano-SiO₂ and ?-PGA.In this study,organic high molecular polymerization method was firstly used to prepare composite film materials with different proportions of Nano-SiO₂,fertilizer synergetic ?-PGA and glutaraldehyde.We measured the hydrophilism,permeability properties,infrared spectrum characteristics and surface microstructure of composite membrane materials to optimize the processing parameters.Then,fluidized bed coating and self-assembly modification technology were used to prepare modified Nano-SiO₂-PVA-?-PGA composite coated fertilizers.The infrared spectrum characteristics and surface microstructure changes of membrane materials were conducted to analyze the mechanism of modified membrane formation.The nitrogen release characteristics and mechanism from different coated fertilizers were studied by soil column leaching test and soil incubation experiment test.At the same time,effects of self-assembly coated fertilizer on rape growth and nitrogen utilization were tested by pot experiment.The main results from the study were listed as followed:?1?The suitable ratio of coating materials was screened out.The water absorption of polyvinyl alcohol-?-glutamic acid composite membrane materials was significantly reduced after adding crosslinking agent,glutaraldehyde.When the concentration of PVA was 4%,mass ratio of ?-PGA to PVA was 1.2:3,and volume fraction of glutaraldehyde was 0.3%,water absorption was the lowest,which was 118%.Nano-SiO₂ addition further decreased the water absorption and permeability of composite material films.When its addition amount was 20 g·kg^-1,water absorption rate and NH₄⁺ permeability of the composite membrane materials were decreased by 6.8%³8.2% and 23.8%⁵3.2%,respectively.With Nano-SiO₂ addition,the stretching vibration peak of-OH was widened,transmittance was increased,so its hydrophilic groups were decreased.Besides,the residual ?-PGA could still play the role of fertilizer synergist.The results of scanning electron microscope showed surface of the composite film was getting smoother and more uniform,which may be the main reason that Nano-SiO₂-PVA-?-PGA coated material films could slow down nitrogen releasing.?2?We prepared the Nano-SiO₂-PVA-?-PGA composite coated fertilizer and its nutrient slow and release mechanism was screened out.The results showed that,with Nano-SiO₂ addition,the nitrogen release of PVA-?-PGA coated fertilizer was slowed.On the 35 th day,58.3% of nitrogen leached from the coated fertilizer.Self-assembly treatment further improved the slow-released effects of coated fertilizer.On the 35 th day,only 48.3% of nitrogen leached from the noval coated fertilizer.The SEM results showed that surface of self-assembly treatment exhibited more compact and smoother,the connection between modified film and urea became denser.Additionally,new chemical bonds were cross-linked,which resulted in enhancing the intermolecular force and excellent nitrogen slow-releasing propersity of nitrogen.In soil incubation experiment,nitrogen release curves were related by the first-order reaction model equation.The incubation temperature and soil water content would affect the change of ammonium and nitrate content.?3?The appliacation effects of Nano-SiO₂-PVA-?-PGA composite coated fertilizer was screened out.Compared with ordinary water-based coated fertilizer,the new coated fertilizer significantly increased the yield by 11.6%.Meanwhile,the soluble sugar and vitamin C content of rape were increased,nitrogen use efficiency was improved by 18.9%.In summary,the self-assembly modified coated fertilizer prepared by Nano-SiO₂,PVA and ?-PGA had a good sustained-release and synergist effect,which was proved an environmental friendly coated fertilizer with both sustained-release and synergistic properties.