Preparation And Characterization Of Environment-Friendly Slow/Controlled Release Fertilizers

Slow-release fertilizers can increase the utilization rate of fertilizers and improve the quality and yield of crops,which had drawn extensive attention.In this paper,two new slow-release fertilizers were synthesized from dimerized fatty acids and sawdust.Dimer acid-based coated controlled release fertilizers not only had excellent controlled release properties,but also improved fertilizer utilization rate;Sawdust cellulose-based water retention fertilizers can not only absorb water and hold water,but also improve soil structure and delay fertilizer release.1.The polyurethane coating materials were synthesized by dimer acid,which coated the urea particles through the drum coating process.Firstly,the dimer acid-based polyester polyol was synthesized by reacting the dimer fatty acid with macrogol-400?PEG-400?.Secondly,polyester polyol reacted with polymethylene polyphenylene isocya-nate?PM-200?to form polyurethane coatings?PU?.In order to further improve the controlled release properties,polyether polyol was introduced to form the modified polyurethane coating materials?MPU?.Polyurethane coated controlled release fertilizers?PUF?and modified polyurethane coated controlled release fertilizers?MPUF?were prepared by coating urea with PU and MPU materials.The structure and properties of the two coating materials were analyzed by FTIR,SEM,NMR and TGA.The results show that compared with PU,the surface of MPU was more delicate and smooth,and cross-section of MPU displayed less micropores,while the PU surface was rough and has a large number of micropores on the cross section of PU;the thermal stability of MPU was improved by 70°C(T_20%),the water contact angle increased by 11°,the water absorption and porosity decreased by 72%and 26%,respectively,and the nutrient release period increased by 67 days.Therefore,MPUF has a better controlled release effect and has a broad application prospect.2.The water retention slow-release fertilizers were synthesized by sawdust.Firstly,the lignin was removed in the sawdust,and then reacted with a certain proportion of acrylic acid,acrylamide and urea under nitrogen at 70°C.Finally,the sawdust-based water retention slow-release fertilizers were obtained.The nutrient release performance of SC-g-PAA/PAM/Urea was studied.The structure and properties of water-retaining fertilizers were analyzed by FTIR,SEM EDS and TGA.In addition,the water absorption and water retention of SC-g-PAA/PAM/Urea were also analyzed.The 30%cumulative nutrient release in the water at 500 min indicated that the fertilizers had a good slow releasse property.The microstructure of SC-g-PAA/PAM/Urea displayed that the surface of the fertilizers were rough and could absorb a large amount of water.In addition,SC-g-PAA/PAM/Urea had excellent water absorption and water retention,which can be extended by 18 days when 2 g of water-retaining fertilizers were added.In addition,the water absorption in the 0.01 mol/L NaCl solution was the highest,108 g/g;the water absorption rate was the highest,231 g/g in the solution with pH 7.This study shows that the water-retaining fertilizers have a water-retaining and slow-release function and have broad prospects in agricultural production.