Study On Preparation Of Multifunctional Fertilizers And Regulation Mechanism Of Nutrient Release

Fertilizer brings convenience to agricultural production.With the improvement of agricultural production technology and the enhancement of people’s awareness of ecological and environmental protection,traditional fertilization methods can no longer meet the needs of smart agriculture in the new age.At the same time,the long-term and high-intensity utilization of land leads to the decline of soil quality to varying degrees.As a plasticizer in mulching film and shed film commonly used in agriculture,DEHP is frequently detected in facility soil.In order to improve crop yield and take into account the concept of coexistence of soil conservation and utilization,environmentally friendly intelligent controlled release fertilizers that respond to the external environment,match the needs of crop growth nutrients,and reduce nutrient loss and ecological pollution stand out among many technologies.Therefore,in this study,the preparation technology of urea and formaldehyde slow-release fertilizer was adopted,and the polymer slow-release fertilizer（SRF）containing nitrogen,phosphorus and potassium was prepared by polymerization of potassium dihydrogen phosphate on the basis of traditional urea and formaldehyde fertilizer.At the same time,the thermosensitive polymer material PNIPAM and sodium alginate loaded with nano-silica were used to form a semi-interpenetrating network polymerization gel,and the polymer slow-release fertilizer was coated to prepare a temperature-sensitive controlled release fertilizer.In addition,the controlled-release fertilizer was innovatively combined with DNHP-S2,a DEHP degradation bacterium screened by the laboratory,to finally prepare the multi-functional fertilizer MF.The prepared multifunctional fertilizer was applied into the soil to preliminarily explore the law and mechanism of nutrient release under actual conditions,and further explore the response of soil nutrient elements inorganic nitrogen and available phosphorus to nutrient release from fertilizer.The effects of pakchoi on plant growth were studied,and the regulation mechanism of multifunctional fertilizer application on soil nutrients was revealed.The main conclusions are summarized as follows:（1）Urea-formaldehyde polymer was prepared in the alkaline environment in the presence of potassium hydroxide and reacted with potassium dihydrogen phosphate to form polymer slow-release fertilizer SRF with polymerization of P and K.Through FTIR analysis and SEM characterization of SRF,FTIR showed that the vibration peaks of-N-H-group,-CH₂-group and P=O group were obtained at 3358cm^-1,2964cm^-1and 1244cm^-1,respectively.SEM showed that the structure of SRF changed compared with the synthetic substance.The linear polymer characteristics showed that the polymer slow-release fertilizer was successfully prepared.（2）PNIPAM-SS semi-interpenetrating network envelope gel formed a semi-interpenetrating network structure under physical cross-linking between PNIPAM and sodium alginate supported nano-silica.FTIR analysis showed that the bonding of sodium alginate with nano-silica significantly enhanced the peak value of Si-O bond at 1102cm^-1.FTIR analysis of PNIPAM-SS showed that the physical crosslinking mode was PNIPAM-SS.The principle of controlled release of its coated gel is as follows:PNIPAM in higher or lower than the LCST,under the temperature response of hydrophilic group and hydrophobic group leading role switch,at the same time due to the adhesion and p H value of the sodium alginate inductance,and under the condition of mild met bivalent ions can rapidly form the properties of the gel,guarantee the stability of the gel in the process of fertilizer release capsule,realize self-healing performance,make PNIPAM coated SRF.The neutral alkaline environment of biochar attached to the coating material provides a habitat for the repair bacteria DNHP-S2 of multi-functional fertilizer.When the fertilizer is released into the environment,the high concentration of salt surrounding the fertilizer reduces the harm to bacteria.（3）The Pseudo second order dynamic equation was used to perform linear fitting for the release of multifunctional fertilizer in complex soil environment,and it was concluded that the release equilibrium time of MF was 88.50 days at 35℃and 84.03 days at 25℃,which were similar to the actual monitoring results.The Pseudo second order dynamic equation could simulate the release process of multifunctional fertilizer in soil.The release of multifunctional fertilizers in soil showed delayed release characteristics.The correlation analysis of nutrient release of multifunctional fertilizer at 35℃and 25℃with inorganic nitrogen and available phosphorus,chemical indexes p H and EC was conducted.The results showed that there was a high positive correlation between temperature and soil NO3--N,NH4+-N,MF-N and MF-P release.（4）The nutrient release and transformation and retention of MF in soil showed time and temperature differences.The addition of MF significantly increased the contents of NO₃^--N,NH₄⁺-N and AP in soil,but had no significant effect on p H and EC of soil chemical properties.Multifunctional fertilizers can respond to the changes of the external environment to regulate the release of nutrients,and release more nutrients in a higher temperature environment.At 35℃,the growth characteristics of Pakchoi were significantly improved,the residual amount of DEHP in soil was decreased,the soil nutrient balance was guaranteed,and the risk of DEHP absorption by pakchoi was reduced.