Preparation And Propertics Of Environmentally Friendly Multifunctional Slow/controll Release Fertilizer

With the increasing public concern toward human health, environmental protection, and natural resource sustainability, there is a shift toward the development of sustainable agriculture that sustains food production with minimal fertilizer nutrient loss. This is an important task of the scientific and technological innovation of agricultural fertilizers. This thesis focuses on the development of efficient, environmentally friendly, low cost multifunctional slow/controlled release fertilizers, based on attapulgite clay as matrix, urea, ammonium sulfate, ammonium chloride, and potassium dihydrogen phosphate as fertilizer raw materials, sodium alginate, guar gum, starch and its derivatives, cellulose derivatives, humic acid, poly(acrylic acid), poly(itaconic acid), polyacrylamide, etc. as coating materials. Granulator was used to prepare a series of multifunctional organic-inorganic coated slow/controlled release fertilizers. The release behavior and mechanism of the products, the influence of the products on soil conditioning, as well as the degradation of the coating materials were determined systematically. The main results are as follows:1. A slow-release multielement compound fertilizer (SMCF) was prepared. The nutrients (H2NCONH2, KH2PO4, and K2Cu3(P2O7)2·3H2O) were entrapped in the alginate matrix granules, and the crosslinked sodium alginate-g-ploy(acrylic acid)(SA-g-PAA) superabsorbent polymer was used as coating. The product could significantly improve the water-holding capacity and decrease the moisture evaporation of soil. Moreover, the partially degradable superabsorbent materials used as coating can alleviate the pollution which was caused by conventional non-degradable superabsorbent polymer materials. The nutrient Cu in K2Cu3(P2O7)2·3H2O showed excellent slow-release property, which is available in the soil so as to be assimilated by plants for a long period.2. A multifunctional double coated slow release fertilizer was prepared based on nutrients urea and potassium dihydrogen phosphate entrapped in the attapulgite clay matrix, sodium alginate used as an inner coating and sodium alginate-g-poly(acrylic acid-co-acrylamide)/humic acid superabsorbent polymer used as an outer coating. The introduction of APT can slow fertilizer nutrients release due to its adsorption capacity and provide abundant nutrients. Natural polymer sodium alginate as coating materials, not only made the process simple, but also can slow fertilizer nutrients release. The superabsorbent used as outer coating not only slowed down the nutrient release, improved water-holding capacity of soil, but also regulated the pH value of soil.3. A multifunctional slow release organic-inorganic compond fertilizer was prepared based on nutrients urea and potassium dihydrogen phosphate entrapped in the attapulgite clay matrix, guar gum used as an inner coating and guar gum-g-poly(itaconic acid-co-acrylamide)/humic acid superabsorbent polymer used as an outer coating. The use of environmentally friendly hydrophilic polymer guar gum as coating materials played a role in controlling nutrient release to some extent based on its high viscosity. The introduction of guar gum and humic acid in the preparation of the superabsorbent polymer guar gum-g-poly(itaconic acid-co-acrylamide)/humic acid not only enhanced water absorption capacities, reduced the cost, improved its degradability, but also provided a kind of organic fertilizers for plant growth. The superabsorbent used as outer coating played an important role in slowing down the nutrient release, improving water-holding capacity of soil, and regulating the pH value of soil.4. An environmentally friendly coated nitrogen fertilizer was prepared based on ethyl cellulose as an inner coating, carboxymethyl cellulose/hydroxyethyl cellulose composite material as an outer coating. Ethylcellulose played an important role in slowing down the nutrient release due to its hydrophobicity and excellent film-forming ability. The degradable composite absorbent material carboxymethyl cellulose/hydroxyethyl cellulose used as outer coating materials can adsorb the nutrition element in the process of absorbing water, which was helpful in retarding nutrient release, improving water-holding and water-retention capacity of soil.5. A controlled release fertilizer system based on starch acetate with high degree of substitution and weakly cross-linked carboxymethyl starch/xanthan gum absorbent with trisodium trimetaphosphate as coating materials was developed to improve fertilizer use efficiency. The N release can be controlled by changing the thickness of coating and the content of plasticizer. The polysaccharide based absorbent material carboxymethyl starch/xanthan gum used as a novel coating played an important role in holding water in soil. Moreover, when the absorbent material was degraded, it can be used as an organic fertilizer to increase soil organic matter content and improve soil fertility.6. The nutrient release behaviors of the several multifunctional slow/controlled fertilizers were determined by burying an amount of products in sealed plastic mesh bags in the soil. The results showed that although the processing is simple with the hydrophilic polymer sodium alginate and guar gum used as inner coatings, the slow release properties were compromised compared with ethyl cellulose and starch acetate. The results of the effect of the multifunctional fertilizer products on water-holding and water-retention capacity of soil showed that, the absorbent materials we prepared played an important role in holding water in soil. Moreover, the composite absorbent materials carboxymethyl cellulose/hydroxyethyl cellulose and carboxymethyl starch/xanthan gum were prepared based on environmentally friendly natural polymer, which could reduce the excessive reliance on petroleum-based products of superabsorbents to some extent. The products with the characteristics of non-polluting and low-cost could be expected to have wide applications.In conclusion, several kinds of environmentally friendly multifunctional slow release organic-inorganic compond fertilizer were prepared in a simple process by using the coating materials with extensive source, low cost, and non-polluting properties. The structural and chemical characteristics of the products, as well as the aspects of performance were examined. This work will lay the theoretical and practical foundation to some extent for expending the types of coated slow/controlled fertilizers and promoting the practical applications.