Development Of Novel Superabsorbent Polymer And Superabsorbent Controlled Release Fertilizer And Mechanism For Improving Soil Water Retention

Drought and low fertilizer utilization are two key constraints in agricultural development.Superabsorbent polymers?SAP?and controlled release fertilizers are two effective measures to alleviate drought and increase fertilizer utilization.In this study,the commercial superabsorbent polymer?CSAP?was used as the starting point.In chinese rose test,water absorption of CSAP was susceptible by soil solution salt ions in actual application.Therefore,the research was carried out through two perspectives:increasing the salt-tolerance of SAP and reducing the salt concentration of soil solutions by applying controlled-release fertilizers.A new type of modified starch SAP?MSSP?was synthesized,and the action mechanisms of MSSP combining controlled-release fertilizers for soil and crops were discussed by simulation conditions and application experment.In addition,a new type of SAP composite coated controlled-release fertilizer was studied to explore the future development of SAPs.First,common compound fertilizer and controlled-release compound fertilizer combined 0,0.25‰and 0.5‰soil quality of CSAP were applied in soil column simulation and potted chinese rose tests,soil water,nitrogen,potassium leaching rate and physiological characteristics of chinese rose growth were studied.Second,the solution-polymerization method was used to prepare an modified starch superabsorbent polymer,and the structure was characterized by scanning electron microscopy and infrared spectroscopy.The single-factor stepwise optimization method was used to optimize the process,water absorption characteristics of MSSP were determined;then compared with CSAP and Starch-grafted superabsorbent polymer?SGSP?,the soil column simulated irrigation test,wheat and corn pot test and cucumber seedling test were conducted to investigate the action mechanism of the SAPs on soil and crops.Third,the studies on new superabsorbent polyurethane composite coated urea was carried out,which mainly included the optimization and structural characterization of the new fertilizer surface in situ reaction composite process,the effects of different preparation processes on the nutrient release and water absorption characteristics of the fertilizer,yield and fertilizer utilization of crop were also studied by corn test.The main results were as follows:?1?The results of the soil column simulation test showed that compared with CCF combined with the same amount of CSAP treatment,the nitrogen and potassium leaching rates of the CRCF treatment were reduced by 72.4%⁷5.6%and 81.5%⁸4.2%,respectively;There was no difference in nitrogen leaching between the two CCF treatments,but with the increase of the amount of CSAP,the amount of potassium leaching decreased significantly by11.6%²6.3%;The results of rose pot test showed that compared with CCF combined with the same amount of CSAP,the CRCF combined with the CSAP increased the early flowering period of rose by 5⁷ days,extended the flowering period by 5¹0 days,and increased plant height by 12.8%³6.0%,and stem thickness increased by 5.4%¹5.2%,which increased the SOD and POD activities of rose leaves by 12.6%³3.0%and 14.5%³1.1%,respectively.CSAP combined with CRCF could significantly improve soil water and fertilizer retention capacity and ornamental values of the rose compared with CSAP combine CCF,it would better meet the growth and physiological requirements of the rose.?2?By sulfamic acid modification,a sulfonic acid group was introduced into the starch,and a modified starch SAP with a maximum swelling degree of 1026 g/g in deionized water and a maximum swelling degree of 145 g/g in physiological saline was synthesized.The optimal synthesis conditions were:sulfamic acid proportion was 1.2%of the starch mass,the dry modified starch to acrylic acid mass ratio was 1?7.5,the acrylic acid neutralization degree was 70%,and the amount of initiator and cross-linker were respectively 3%and 0.15%acrylic acid weight.The swelling ratios in simulated different pH and salt concentration solutions were significantly higher than CSAP and SGSP.The soil column simulated irrigation experiment showed that:compared with CSAP and SGSP treatments,MSSP significantly reduced the leachate volume by 8.9%and 7.3%,the total nitrogen leaching rates were reduced by 28.7%and 31.0%,and the ammonium nitrogen leaching rates were reduced by 75.3%and 56.7%,Nitrate nitrogen leaching rates were reduced by 22.2%and 22.8%;MSSP significantly increased nitrogen adsorption by 55.3%and 309.4%,and potassium adsorption was significantly increased by 80.0%and 53.7%.Computed tomography experiments showed that MSSP significantly increased the number and proportion of soil pores by 244.3%⁴34.6%and38.1%¹77.8%compared with CSAP and SGSP.The crops experiments showed that the application of MSSP significantly increased the total nitrogen,nitrate nitrogen,available potassium content,and leaf SPAD values in the true solution of the 2018 summer corn soil,thereby significantly increased 25.9%³2.1%of summer corn yield,32.7%⁴5.3%of nitrogen utilization rate,29.3%⁹9.1%phosphorus utilization rate,24.0%potassium utilization rate,and13.6%²9.4%water utilization rate,respectively;The cucumber seedling test showed that applying MSSP significantly increased the root tip number of cucumber seedlings by 23.6%,and improved SPAD value and photosynthetic capacity of leaves.So,compared with CSAP and SGSP,MSSP significantly improved soil water and fertilizer retention capacity and porosity,promoted crops to absorb water,nutrients,crop photosynthesis,and root growth were also incresed,thereby increasing yield.?3?A novel type of composite coating process of superabsorbent polyurethane coated urea?SAPCU?has been developed.Infrared spectroscopy,X-ray diffraction,thermogravimetric analysis,and scanning electron microscopy were used to determine the chemical structure,thermal stability,and micromorphology of the novel water-absorbent controlled release urea.The results show that a superabsorbent polyurethane?SAPU?composite coating was formed by in situ reaction,in which the redundant isocyanate groups in castor oil polyurethane?COP?react with a large number of hydroxyl groups in MSSP to form a urethane bond to connect MSSP powder,MSSP stacked into a film to form a gradual composite coated urea structure of COP-SAPU-SAP;By measuring the nutrient release characteristics and water absorption characteristics of SAPCU,different nitrogen release and water absorption characteristics of SAPCU could be obtained by adjusting the amount of castor oil polyurethane and SAPU.The SAPCUs had a high total nitrogen content of 40.2%⁴2.1%,swelling ratios of120¹60g/?g SAPU?^-1,and nitrogen release period of 60¹50 days.Corn pot experiments showed that SAPCU significantly increased the nitrogen utilization rate by 9.6%compared with the MSSP-blended controlled-release fertilizer application method.In summary,this research improved the shortcomings of poor salt resistance of traditional SAPs by synthesizing new modified starch SAP.Clarified the mechanism of the SAP to improve soil nutrient elements and water availability,increase crops'ability to absorb water,nutrients,and promote photosynthesis and root growth to increase yield.A new synthetic process of water-retaining and controlled-release fertilizer was proposed,and a full-flow technical system for the SAP production,evaluation in the laboratory,mechanism of action,and a variety of SAP-controlled-release fertilizer compound application technologies were constructed.