| Our country use of the world’s seven percent of arable land to feed 22% of the world’s population, fertilizer plays an important role in the guarantee of national food security. However, brings long-term excessive fertilization not only causes a huge waste of resources, but also brings a lot of environmental problems. Slow/controlled release fertilizer can effectively control the release rate of nutrients and prolong the period of fertilizer. It can improve fertilizer use efficiency and reduce environmental problems caused by nutrients loss. In addition, it can improve the economic efficiency of fertilization and guarante the quality of agriculture products, which is of great significance for the sustainable development of agriculture. This thesis focuses on the development of environmentally friendly, biodegradable, low-cost multifunctional slow/controlled release fertilizer, based on inorganic clay mineral of palygorskite as matrix, urea and slightly soluble ammonium zinc phosphate and ammonium polyphosphate as fertilizer raw materials, chitosan, konjac glucomannan, polyvinyl alcohol, methyl cellulose, cellulose acetate butyrate, and wheat straw of biomass resources as raw materials. Two types of multifunctional organic-inorganic compound slow release fertilizers were prepared by coating method and adsorption. The nutrients content of two types of multifunctional slow release fertilizer, the release properties of nutrients in the soil, the degradation of the coating materials, the influence of the products on water-retention capacity of soil, as well as the function of improving the soil conditioning were investigated in details. The main results are as follows:1. A multifunctional controlled release fertilizer was prepared based on nutrients of urea and ammonium zinc phosphate entrapped in the attapulgite clay matrix, cellulose acetate butyrate as an inner coating and carboxymethyl chitosan-g-polyacrylic/attapulgite superabsorbent polymer used as an outer coating. The contents of the nitrogen (N) and zinc (Zn) of the product were 27.1% and 0.72%, respectively. The product has the preferable slow release property. The superabsorbent used as outer coating not only can slow down the nutrient release rate, but also can improve the water-holding and water-retention capacity of soil. The outer coating of superabsorbent can also promote to amelioration of soil, and it played an important role in regulating the pH value of soil. The introduction of modified natural polymers of carboxymethyl chitosan and biodegradable crosslinkers of N-maleyl chitosan into the superabsorbent polymer can improve the coating degradation. The outer coating material can also improve the water-retention capacity of soil, while avoiding residues in soil cause secondary pollution to the environment. The micronutrient zinc fertilizer was synthesized, which has preferable slow release property. It can be used as a long-term effectiveness micronutrient element zinc fertilizer and used with other base fertilizer.2. A double-coated multifunctional slow release fertilizer was prepared. The urea and ammonium polyphosphate were entrapped in the konjac glucomannan matrix, polyvinyl alcohol/methyl cellulose blend material as an inner coating and konjac glucomannan-g-poly(N-(2-hydroxypropyl)methacrylamide)-co-2-acrylamide-2-methylpropane sulfonic acid) superabsorbent polymer used as an outer coating. The contents of the nitrogen (N) and phosphorus (P2O5) of the double-coated fertilizer were 18.4% and 8.72%, respectively. The double-coated slow release compound fertilizer has the preferable slow release property. The outer coating of KGM-g-P(HPMAm-co-AMPS) superabsorbent prepared by graft polymerization can not only slow down the nutrient release rate, but also improve the water-holding and water-retention capacity of soil. The introduction of natural polymer into the superabsorbent can improve the outer coating degradation.3. A novel amphoteric straw adsorbent was prepared by chemical modification of pretreatment wheat straw. The adsorbent was prepared by using wheat straw as raw materials, which can effectively adsorption removal of NH4+ and H2PO4-. Furthermore, the recovered nutrients-enriched adsorbent materials can be reused as a multifunctional slow release compound fertilizer. It can not only slow down the nutrient release rate, but also improve the water-holding and water-retention capacity of soil. The results of adsorption studies showed that the adsorption with both NH4+ and H2PO4- were quickly, and the adsorption could reach equilibrium within 20 and 30 min, respectively. The adsorption kinetics of both NH4+ and H2PO4- onto adsorbent were well described by pseudo-second-order model. The equilibrium adsorption capacity of adsorbent for NH4+ was 68.4 mg g-1 at abroad range of pH from 5 to 8, while it was 38.6 mg g-1 for H2PO4-at pH values ranged from 4 to 8. The adsorption isotherms of amphoteric straw adsorbent for both NH4+ and H2PO4- were well described by Langmuir model. The adsorption process is mainly physical adsorption, and it is a spontaneous and exothermic process. The contents of the nitrogen (N) and phosphorus (P2O5) of the multifunctional slow release compound fertilizer were 7.81% and 0.7469 mg g-1, respectively. The multifunctional slow release compound fertilizer was prepared by using resource-rich straw as raw materials, which is low-cost and environmentally friendly. The preparation method provides a new way of using the crop resources, which are benefit to the development of economic, environmental and social.4. A novel nanocomposite hydrogel was prepared by in situ graft polymerization. The as-prepared palygorskite nanocomposite can be used as a highly efficient adsorbent to removal and reclaim NH4+ from ammonium wastewater. Furthermore, the recovered nitrogen-enriched adsorbent can be used as multifunctional slow release nitrogen fertilizer. It can not only slow down the nutrient release rate, but also improve the water-holding and water-retention capacity of soil. The adsorption kinetics of NH4+ onto adsorbent was quickly, and the adsorption could reach equilibrium within 10 min. The adsorption isotherm of NH4+ onto adsorbent was well described by pseudo-second-order model. The as-prepared adsorbent has good affinity to NH4+, with the adsorption capacity of 237.6 mg g-1 when 30 wt% PGS is incorporated. The equilibrium adsorption isotherm can be well described by Freundlich model. The results indicate that the adsorption of NH4+ onto adsorbent is a spontaneous and exothermic process. The content of the nitrogen (N) of the multifunctional slow release nitrogen fertilizer was 13.2%. The preparation method of multifunctional slow release compound fertilizer is simple, and the fertilizer is low-cost and biodegradable. The introduction of palygorskite into nanocomposite material, can not only improve the adsorption capacity of the adsorbent, but also slow down the release rate of nutrients. |
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