Study On Preparation,Degradation Mechanism And Application Effect Of Novel Organic Polymeric Slow And Controlled Release Fertilizers

Compared with quick release fertilizers,slow and controlled release fertilizers have some advantages in increasing the fertilizer utilization efficiency,reducing environmental pollution and increasing crop yield.At present,the commercially available slow and controlled release fertilizers at home and abroad are usually coated fertilizers and urea-formaldehyde fertilizer.However,the membrane shell materials of the coated fertilizers are usually difficult to degrade,and causing secondary pollution in the soil.The coating process is a multistep preparation procedure,leading to the increase of production cost.Urea-formaldehyde fertilizer is only applied to perennial plants,such as forests,lawns,and so on,just because of the long release cycle of nutrient N.Three novel slow and controlled release fertilizers with environmentally friendly,low-cost and high-efficiency were developed by this paper.Their synthesis mechanisms were completely different from the various fertilizers reported by literature to date,and can effectively solve many defects of the existing slow and controlled release fertilizers.In addition,a series of biodegradable organic polymeric slow and controlled release fertilizers were successfully prepared by our group previously.However,their application effects,the degradation mechanisms and the impact of microstructure on the slow release rate of nutrients are still missing.Thus,the tomatoes pot experiments were employed to study the application effects of different types of slow and controlled release fertilizers.Moreover,the relationship of molecular structure,degradation mechanism and slow release properties of the typical biodegradable polymeric slow and controlled release organic fertilizer containing nutrient NPK was also studied by this paper.The specific research contents of this paper are as follows:?1?A new granular slow-release fertilizer prepared by a cold extrusion strategy?GSRFEx?based on urea-formaldehyde?UF?,ammonium polyphosphate?APP?and amorphous silica gel?ASG?was presented.Characterizations showed that there were a strong hydrogen bond interaction and good compatibility among UF,APP and ASG in GSRFEx.Mechanical properties as well as slow-release properties of GSRFEx were greatly enhanced after adding APP and ASG into UF.Rape pot experiments indicated that GSRFEx could improve N use efficiency dramatically and thereby facilitate the growth of rapes.Importantly,as an economical,effective and environment-friendly technology,the cold extrusion had a great potential to be applied in horticulture and agriculture.We hope that our work could offer an alternative method for the design of slow-release fertilizer with desirable properties.?2?A new semi-interpenetrating polymer networks?semi-IPNs?slow-release fertilizer?SISRF?with water absorbency,based on kaolin-g-poly?acrylic acid-co-acrylic amide??kaolin-g-P?AA-co-AM??network and linear urea-formaldehyde oligomers?UF?,was prepared by simple solution polymerization.The structure and properties of SISRF were characterized by various characterization methods.Results suggested that SISRF showed excellent ability to control the slow release of nutrient NPK,and exhibited water absorbency of 68 g/g in tap water.The formation of SISRF with simultaneously good slow-release and water-retention capacity was expected to apply in modern agriculture and horticulture.Meanwhile,the swelling kinetics was well described by pseudo-second-order kinetic model.?3?A new biodegradable polymeric slow and controlled release organic fertilizer containing nutrient N and P was prepared by the polycondensation of urea phosphate with urea-formaldehyde prepolymer.Results indicated that the fertilizer showed good slow release of nitrogen and phosphorus nutrients,and could improve long-term fertility of soil.?4?Application effects of different types of biodegradation organic polymeric slow and controlled release fertilizers were studied by the tomatoes pot experiment.Principal component analysis and cluster analyses were applied to achieve a comprehensive assessment on the effects of different slow and controlled release fertilizers on soil fertility.The results showed that different biodegradable organic polymeric slow and controlled release fertilizer treatments had significant effects on improving the chlorophyll content in leaf,actual yield and fruit quality of tomatoes.Among them,actual yield of the biodegradable organic polymeric slow and controlled release fertilizer containing nutrient Si?GRF?was optimal,and fruit quality of the biodegradable organic polymeric slow and controlled release fertilizer containing nutrient NPK?PRF?was best.The soil fertility quality could be classified into three categories by principal component and cluster analyses,corresponding to high quality soil?the biodegradable organic polymeric slow and controlled release fertilizer containing nutrient Fe-Mn-Cu-Zn?WRF?and GRF?,medium quality soil?PRF and urea formaldehyde fertilizer?UF?,the biodegradable organic polymeric slow and controlled release fertilizer containing nutrient B?BRF??and low quality soil(blank control?CK and conventional organic-inorganic compound fertilizer?OM+CCF??.Therefore,biodegradable organic polymeric slow and controlled release fertilizers could really alter the balance of soil nutrients,enhance soil fertility comprehensively in the aspects of soil physical and chemical fertilities,and improve the supply ability of soil nutrients.?5?The essence of the biodegradable organic polymeric slow and controlled release fertilizer containing nutrient NPK is KH₂PO₄?KDP?molecularly amended urea-formaldehyde?KDP-UF?,there have been reports in the literature recently,and which can improve the slow release properties of nutrients and increase the soil fertility and crop yield.However,until now,the underlying degradation mechanisms and the impact of KDP-UF microstructure on the slow release rate of nutrients are still missing.Here,we identify why KDP-amended molecularly urea-formaldehyde helps to optimize its slow release properties.Fourier transform infrared spectroscopy,X-ray diffraction,X-ray photoelectron spectrometry and scanning electron microscopy demonstrate that a large part of KH₂PO₄ and urea-formaldehyde chains are essentially held together with hydrogen bonds,which promotes the degradation rate of UF matrix and further enhances N-slow release rate.This implies that the functioning of KDP-UF is mainly determined by the formation of intermolecular hydrogen bonds between UF and KH₂PO₄,rather than the copolymerization of UF and KH₂PO₄ reported in previous literature.