Preparation And Properties Of Environment Friendly Slow Release Urea With Water Retention

Water and fertilizer are two important factors in agricultural production.Shortage of water resource,regional disparity and conventional low utilization rate of fertilizer have restricted the sustainable development of China agriculture.Slow-release fertilizers with water-retention,combined slow release fertilizers and water absorbent material,is a new technology to enhance the efficiency of fertilizer and water,reduce the times of fertilization and irrigation,and has been a new direction of fertilizer research at home and abroad.In this paper,firstly,a series of membrane materials were prepared and optimal conditions were studied.And,physical and chemical methods were applied to evaluate and investigate the structure,water absorption,degradation,antibacterial and nutrient absorption of membrane materials.Furthermore,slow-release urea with water-retention(WRACU)was prepared by aqueous solution polymerization,which the membrane material was directly synthesizied on the urea surface.And the structure,nutrient release ability and integral regulation and control of water and fertilizer effect to be evaluated and investigated.The main conclusions are as follows:(1)Using sodium alginate(SA),kaolin(KL),acrylic acid(AA)and acrylamide(AM)as raw materials,N,N-Methylenebisacrylamide(MBA)as the cross-linking agent and potassium persulfate as the initiator,degradable membrane material was synthesized by aqueous solution polymerization.When the dosage of SA,AM,KL,MBA and initiator were9wt%,40wt%,7wt%,0.04wt%and 0.16wt%of total monomer mass,respectively,the reaction continued at 80?for 2 h.The water absorption rates of the membrane material(WRA1)were 308g.g^-1and 56 g.g^-1,in pure water and saline water,respectively.SA could enhance the biodegradability of the membrane material.With the dosage of SA increasing from 0 to 12wt%of total monomer mass,its degradation rate in soil increased from 3.02%to 25.98%,and increased with the increased dosage of SA.(2)Quaternary ammonium salt(RADM)and Nano-Ti O₂were introduced into the membrane material to improve its antibacterial property,reduce the loading quantity of microorganism on the surface of the membrane material,thus reducing the degradation rate.With the increased dosage of RADM,the antibacterial property of membrane material resin was enhanced.When the dosage of RADM was 3wt%of total monomer mass,the antibacterial rate to fungus,bacillus subtilis and soil bacteria suspension were 62.67%,32.40%and 31.74%,respectively.The microorganism growth experiment indicated that RDMA could reduce the loading quantity of microorganism on the membrane material.Therefore,the degradation rate of the membrane material in soil can be adjusted by regulating the dosage of RADM.Nano-Ti O₂could play the roles of antibacterial and improving the photodegradation with light resources.Considering the degradability and water absorption ability of the membrane material,the proper reaction conditions were determined as(which the membrane material(WRA2)was prepared according to this):the dosage of RADM and Ti O₂were 2wt%and 1wt%of total monomer mass,other reaction conditions were the same as(1).(3)The two kind of membrane materials prepared not only had the water absorption ability but also had the adsorption property for nutrients.In the urea solution and the co-existence system of urea and monopotassium phosphate solution,the adsorption quantity for nutrients increased with the increased concentration of nutrients.The application of membrane material in soil could improve the nutrient utilization efficiency and water utilization efficiency,reduce the leaching loss of nutrients,improve the biomass of crops,increase the nutrient residue in soil and prolong the fertilizer efficiency.Comparing to the control,under the application dosage of 1 g WRA1 or WRA2 per kilogram soil,the water utilization rate was improved by 10.93%and 19.53%,the utilization rate of nitrogen was increased by 54.53%and 47.21%,while the corn biomass was improved by 6.80%and 19.50%.And the alkali-hydrolyzable nitrogen,available phosphorus and rapidly available potassium of soil were improved by 8.18%and15.29%,23.48%and 42.41%,17.92%and19.79%.(4)Based on(1),water retention slow-release urea(WRA1CU)was successfully prepared by aqueous solution polymerization,which the membrane material was directly synthesizied on the urea surface.Moreover,the structure of WRA1CU was characterized by scanning electron microscope(SEM)and infrared spectrometer(IR).There was a distinguishable interface between the coated material and the core urea under the SEM.Indicating the membrane material was closely adhered to the core urea and there was also some holes.The coated layer was even and compact.Through the IR analysis,there was no reaction between the membrane material and the core urea.(5)Based on(2),a series of water retention and slow-released urea(WRA2CU)was prepared.The influence of the dosage of RDMA and Nano-Ti O₂,and the coated rate on the performance of WRA2CU was investigated and the structure of WRA2CU was characterized by SEM and IR.Nano-Ti O₂had almost no influence on the water absorption and initial nitrogen dissolution rate of the WRA2CU.While RDMA could improve the water absorption and reduced the initial nitrogen dissolution rate.SEM graph displayed that the surface of the WRA2CU was more compact and rough,and has a larger specific surface area than the WRA1CU.Meanwhile,there was also no reaction between the membrane material and the core through IR analysis.(6)WRACU could improve the soil maximum water holding capacity,with the increasing range as 8-20%and reduce the ammonia volatilization loss of fertilizer in soil by over 70%,compared with urea.The 7D solution rate test and soil column leaching experiment indicate that:the initial nitrogen dissolution rate of WRACU was about 30%and the cumulative nitrogen dissolution rate of 7 days was 80%in deionized water,while the nitrogen dissolution rate at the 1st day was only 21.20%and the cumulative nitrogen dissolution rate of 4 weeks was 52.31%in soil.Pot experiments showed that:compared with urea,the corn biomass improved by 10%or above,the water and the nitrogenuse efficiency increased by 24.50%and 73.50%.The nitrogen and the potassium leaching loss reduced by 20.27%and 26.23%,and it barely had influence on the leaching loss of phosphorus.And the alkali-hydrolyzable nitrogen,available phosphorus and rapidly available potassium of soil were improved by 8.0%,70.92%and 8.67%.The study indicatied that the prepared WRACU behave good biological effects and huge application valuation in agriculture.