Synthesis And Characterization Of Bentonite-based Slow-release Nitrogen Fertilizers With The Function Of Water Retention

In view of the low utilization rate of fertilizer and the shortage of water resources in modern agriculture,several types of slow-release fertilizers with the function of water-retention,based on bentonite clay as matrix,urea and ammonium chloride as fertilizer source,sodium alginate,acrylic acid,acrylamide,2-acrylamide-2-methylpropanesulfonic acid,polyvinylpyrrolidone and cotton stalks were used as raw materials,were prepared in this thesis by inverse suspension polymerization and microwave-assisted synthesis method.The structure and properties of samples were characterized through various analysis technologies.The water absorbency and slow-release properties of the product,and the effect of product on growth of cotton plants were systematically investigated.The main findings are as follows:1.A novel p?AA-co-AM?/Bent/urea slow release fertilizer contained 14.98% nitrogen was prepared via inverse suspension polymerization using acrylic acid,acrylamide,bentonite and urea as raw materials.The sample had a water absorbency of 1527.8 g/g in distilled water and 62-205.6 g/g in the salt solution of 0.05-0.25 mol/L?NaCl,MgCl₂,CaCl₂,BaCl₂,FeCl₃?.The water absorbency of the product decreased with increases in saline solution concentration,cation charge,and cation radius.The water absorbency initially increased and then decreased with increased temperature and pH.The accumulative release rate of the product was not above 80% on the thirtieth day in different environment,indacting the sample had excellent slow release property.The release rate decreased with increases in saline solution concentration,cation charge,and cation radius,and the release rate increased with increased temperature and pH.2.A novel NaAlg-g-p?AA-co-AM?/Bent/urea slow release fertilizer contained 13.55% nitrogen was prepared via microwave irradiation using sodium alginate,acrylic acid,acrylamide,bentonite and urea as raw materials.The sample had a water absorbency of 1220 g/g in distilled water and 22.3-287 g/g in the salt solution of 0.05-0.25 mol/L?NaCl,KCl,NH4 Cl,MgCl₂,CaCl₂,AlCl₃,FeCl₃,Na2SO4,Na3PO4?.The addition of the sample to soil could improve the water-retention capacity of soil.The sample exhibited excellent slow-release properties with 56.1% of nutrients were released after 30 days.The germination rate of the sample treatments increased by 18.32% in comparison to that of the pure urea treatments.3.A semi-interpenetrating polymer network CS-g-PAA/Bent/PVP/urea slow-release fertilizer contained 13.55% nitrogen was prepared via microwave irradiation using cotton stalks,acrylic acid,polyvinylpyrrolidone,bentonite and urea as raw materials.The sample had a water absorbency of 1018.4 g/g in distilled water.The addition of the sample to soil could improve the water-retention capacity of soil.The sample exhibited excellent slow-release properties with 60.8% of nutrients were released after 30 days.The sample possessed lower N leaching loss amount of 10.3% compared with urea.The germination rate of the sample treatment increased by 22.04% compared with that of urea treatment.Plant height,root length,fresh weight,and dry weight of cotton seedlings treated with the sample increased by 25.23,29.47,40.22,and 53.33% compared with urea treatment,respectively.4.A novel biochar-based CS-g-p?AA-co-AMPS?/Bent/N-BC slow-release nitrogen fertilizer contained 5.6% nitrogen with the function of water-retention was prepared via microwave irradiation using cotton stalks,acrylic acid,2-acrylamide-2-methylpropanesulfonic acid,bentonite and NH₄⁺-loaded biochar as raw materials.The addition of the sample to soil could improve the water-retention capacity of soil.The sample exhibited excellent slow-release properties with 69.8% of nutrients were released after 30 days.The sample possessed low nitrogen leaching loss amounts?10.3%?,nitrogen migrate-to-surface loss amounts?7.4%?,and high nitrogen use efficiency?64.27%?,as compared to NH4 Cl.The germination rate of the sample treatment increased by 10.00% compared with that of NH4 Cl treatment.Plant height,root length,fresh weight,and dry weight of cotton seedlings treated with the sample increased by 42.65,25.78,68.94,and 50.00% compared with NH4 Cl treatment,respectively.Comprehensive comparison of the equilibrium water absorbency,the water-retention ratio within 30 days,the accumulative release ratio within 30 days,nitrogen content,cost,biodegradability,and other factors of four fertilizer samples indicated that the comprehensive performance of CS-g-PAA/Bent/PVP/urea has significantly superiority over other three fertilizer samples,and the proposed sample have great potential for wide application in modern agriculture.Furthermore,microwave irradiation would be a promising method to produce slow release fertilizers.