Modified Bio-based Polymer As Coating Material For Controlled-release Urea And Its Controlled-release Characteristic And Mechanism

Controlled-release coated fertilizer can regulate and control nutrient release,improve fertilizer use efficiency and crop yield,and effectively reduce the negative impact of nutrient loss on the environment.However,the coated materials of the controlled-release fertilizers are usually from petroleum-based materials,which are non-renewable,non-biodegradable,have potential risk to environment and are against sustainable development.Moreover,the price of petroleum-based coated fertilizers is expensive,which further brings a series of environmental and economic problems.At present,bio-based coating materials with low-cost,renewable and green property for controlled-release fertilizers have great advantages and thus becomes a hot topic,but there are two major shortcomings of bio-based materials:one is that they contain hydrophilic groups and are easy to absorb water;the other is that there are some substances which do not react with the curing agent to form the coating.They may be released from the coating shells during N release.Their release may enlarge the micropores in the coating shells resulting in fast N release,which is a bottleneck problem restricting the development of controlled-release fertilizer.In addition,although plentiful studies have reported that coated controlled-release fertilizers can improve NUE and crop yield,the mechanism is seldom researched.In order to solve these problems,liquefied wheat straw and corncob based polyols and castor oil-based polyols were used to react with MDI to produce novel bio-based polyurethane(BPU),and superhydrophobic modification technology was used to modify these BPUs to construct a superhydrophobic bio-based coating materials,which enhanced the hydrophobicity of the coating material and improve its nutrient controlled release performance.Furthermore,the mechanism of superhydrophobicity increase the controlled release performance of the bio-based coating material was explored.In addition,castor oil-based polyols were modified by self-assembly and self-healing technology in order to reduce the porosity of bio-based coating material and improve its hydrophobic properties.Finally,the application of controlled-release urea on direct-seeded rice and transplanted rice system was conducted through field experiments to explore its effect on yield,enzyme activity,gene expression,NUE and soil nutrient.The mechanism of controlled-release urea increased rice yield and NUE was explored through gene expression detection.The main results are as follows:1.Bio-based polyurethane(BPU)coated fertilizer(BPCF)prepared from liquefied wheat straw(LWS).BPU was modified by organosilicon(OS)and nano-silica(NS)in order to improve the nano-scale surface roughness of BPU and reduce the surface energy to make it superhydrophobic.A superhydrophobic modified bio-based coated urea(SBPCF)was prepared.Compared with the smooth and porous surface of unmodified BPCF,many nano-scale rough bumps were observed on the surface of SBPCF,and the nutrient release characteristics of SBPCF were significantly improved.This is because the nanoscale surface roughness of SBPCF prevented the direct contact between water and coating materials and formed an air layer between the film and the water,which slowed down the water entering into the film and nutrient dissolving out of the film,thus greatly enhanced the release performance.In addition,nanoparticles on the surface of SBPCF also blocked the micropore on the membrane,which further slowed down the water entering the membrane and enhanced the release characteristics.The results showed that the superhydrophobic modification technology formed superhydrophobic interface on the surface of controlled-release fertilizer,which slowed down water entering the film and improved the controlled-release characteristics of bio-based coated fertilizer.2.Bio-based polyurethane derived from liquefied corncob coated urea(BCU)was synthesized.The organosilicon(OS)was used to modify the BCU to obtain OS modified BCUS(SBCU),which improved the hydrophobicity of the coating.In addition,OS and nano-silica(NS)was used to further modified BCU to get superhydrophobic liquefied corncob-based coated urea(SSBCU)to achieve superhydrophobicity by reducing surface energy and improving nano-roughness of membrane surface.Moreover,the dispersion and preparation process of nano-materials are greatly simplified,and the production cost is reduced.After superhydrophobic modification,the release characteristics of SSBCU were significantly enhanced,followed by OS modified SBCU and unmodified BCU.Compared with the unmodified membranes,the pore size and hydrophobicity of the modified membranes are also significantly reduced.3.Nano lauric acid copper(NLAC)were synthesized by one-step method using ethanol and water as solvents.The nano-material was successfully used to modify castor oil biopolyurethane to produce superhydrophobic modified bio-based coated fertilizer(SNPCF).Compared with unmodified bio-polymer coated fertilizer(PCF),SNPCF significantly improved the release characteristics,increased the release characteristics.Also,there was air shield observed between the superhydrophobic surface and the water,which could slow down the water entering and nutrient dissolving out of the film.Moreover,NLAC was also sprayed on different substrates such as paper,metal,glass and non-woven fabrics to make its surface superhydrophobic and super-lipophilic.The oil-water mixture can be effectively separated by using the nano-material coated non-woven fabric and 100 mesh nylon mesh,which had high separation efficiency and reusability.In addition,nanomaterials exhibit good antimicrobial activity and long-term stability.Overall,this novel nano-copper materila is easy-prepared,low-cost,multi-functional coating material,which has great potential application in many fields in the future.4.In this study,castor oil-based polyurethane coated urea(PCU)was prepared by the reaction of castor oil-based polyols and MDI.Then,the above materials were modified by layer-by-layer self-assembly technology to prepare self-assembly modified castor oil-based polyurethane coated urea(SPCU).Furthermore hollow nano-silica particles were used to modify the SPCU that load with the sodium alginate to obtain self-assembly and self-healing castor oil-based polyurethane coated urea(SSPCU).The nutrient release rate of SSPCU was the slowest,and the nutrient release rate of SPCU was significantly slower than that of PCU.It was also observed that the micropore of SSPCU was repaired and the number of micropore was reduced.It indicated that self-assembled self-repairing bio-based coating material was successfully prepared.The self-assembly and self-healing mechanism was revealed and the release characteristics was enhanced,which solved the bottleneck problem in the production of controlled release fertilizer,and provides important theoretical and technical support for the development of"environmentally friendly,highly efficient,resource-regenerated"controlled release fertilizer.5.A three-year field experiment was conducted.The effects of four controlled release nitrogen(N)fertilizers(120,180,240 and 360 kg N ha^-1;CRU1,CRU2,CRU3 and CRU4,respectively),conventional urea fertilizer(360 kg N ha^-1;U)and control(no N fertilizer;CK)on gene expression,lodging index,yield,biomass,nitrogen use efficiency(NUE)and soil nutrients of direct seeding rice were studied.The results showed that CRU could significantly increase the expression of nitrogen-related genes and lodging resistance of direct-seeded rice,and CRU could also increase the concentration of NO₃^--N and NH₄⁺-N in rice root zone,especially in the late stage of rice growth,and reduce the leaching of N.The rate of continuous release of nitrogen by CRU was well matched with that of rice demand for nitrogen.The grain yield of rice treated with CRU3 and CRU4 increased by 20.8%and 28.7%respectively compared with that treated with U.Moreover,compared with U,all CRU improved NUE.In conclusion,the application of CRU on direct-seeded rice improved the expression of nitrogen-related genes and lodging resistance,increased yield and NUE and reduced nitrogen leaching.6.The mechanisms of how controlled-release urea(CRU)improves N use efficiency(NUE)and yield in relation to quantitative gene expression of two rice cultivars were investigated with a 2-year field experiment.Soil and water N concentrations in the root zone,root development,enzymes activity,biomass and yield,NUE and N related genes expression amount were determined.The results indicated that,compared with conventional urea,CRU application contributed to improved N concentrations in the root zone,N efficient uptake,increased expression amount of N related genes,enhanced synthesis of protein and enzyme,and ultimately high grain yield and NUE.The gene expression amount of Os NIA(encoding a nitrate reductase assimilator),Os GS(encoding a glutamine synthetase assimilator)and Os GLN(encoding a glutamate synthase assimilator)exhibited a positive correlation with yield.The mechanism involves synchronized release of N by CRU with N requirement of rice cultivars,which enhanced root development and signaled production of N related genes,then further enhanced synthesis of protein and enzymes to absorb,transport and use N,contributing to improved NUE and grain yield.The results suggest that CRU can reduce N loss with huge potential for application in rice production system.