Studies On The Preparation And Properties Of Water-retention And Slow-release Fertilizers

In this thesis, we prepared several types of slow release fertilizers with the function of water-absorption and water-retention, which can improve the utilization of fertilizer and water resources at the same time. The effects of reaction conditions such as the contents of monomers, initiator, crosslinker and the neutralization degree of acrylic acid on the water absorbencies were studied systematically. The samples were characterized by FTIR and SEM. The slow release properties of samples in soil, the largest water-holding ratio and the water retention properties of soil with samples were also investigated. The slow release mechanisms of the samples in soil were speculated. The diffusion kinetics of urea in hydrogel was also studied. The main conclusions were drawn as followings:1. Using acrylic acid, polystyrene, urea and ammonia as the main materials, we prepared a coated urea fertilizer with the function of slow release and water retention, which possessed the three-layer structure: the core was urea granule, the inner coating was polystyrene, and the outer coating was crosslinked poly(acrylic acid) containing urea. The fertilizer contained 33.6% nitrogen, and its water absorbency was 76 g/g in tap water at atmospheric pressure. The slow release property of the sample could be adjusted by the thickness of inner coating, and the slow release mechanism of nutrient was speculated. This provided a theoretical basis for the realization from slow release to control release.2. Using acrylic acid, urea formaldehyde, urea, ammonia and attapulgite as the main materials, a coated nitrogen fertilizer with the function of slow release and water retention was prepared, which possessed the three-layer structure: the core was urea granule, the inner coating was urea formaldehyde (a kind of insoluble fertilizer), and the outer coating was crosslinked poly(acrylic acid)/attapulgite composite. The fertilizer contained 28.3% nitrogen, and its water absorbency was 80 g/g in tap water at atmospheric pressure. The introduction of attapulgite reduced the cost of the sample and enhanced its swelling properties. The slow release property of the sample could be adjusted by the molecular weight of urea formaldehyde and the thickness of inner coating. 3. Using acrylic acid, acrylamide, magnesium ammonium phosphate, urea, ammonia and sodium humate as the main materials, a coated urea fertilizer with the function of slow release and water retention was prepared, which possessed the three-layer structure: the core was urea granule, the inner coating was magnesium ammonium phosphate (a kind of insoluble fertilizer), and the outer coating was poly(acrylic acid-co-acrylamide)/sodium humate. The fertilizer contained 26.3% nitrogen, and its water absorbency was 95 g/g in tap water at atmospheric pressure. The introduction of sodium humate reduced the cost of the sample and enhanced its swelling properties, and sodium humate was useful to plant. The slow release property of the sample could be adjusted by the thickness of magnesium ammonium phosphate coating.4. Using acrylic acid, acrylamide, urea formaldehyde, polyphosphate potassium, sodium alginate, kaolin and ammonia as main materials, controlled release NPK compound fertilizer with the function of water retention was prepared, which possessed the core/shell structure: its core was urea formaldehyde and polyphosphate potassium fertilizer, and the shell was poly(acrylic acid-co-acrylamide)/kaolin. The N, P and K contents were 11.3, 21.1 (shown by P₂O₅) and 8.6 (shown by K₂O) wt% respectively, and its water absorbency was 91 g/g in tap water at atmospheric pressure. The change of temperature could control the release rates of N, P and K nutrients.5. A series of poly(acrylic acid-co-acrylamide)/kaolin (poly(AA-co-Am)/kaolin) composites were prepared by aqueous solution copolymerization of partially neutralized acrylic acid and acrylamide in the presence of kaolin powder, which was synthesized to as a release carrier of urea fertilizer. The superabsorbent composite was swollen in urea aqueous solution to load urea. Urea diffusion coefficient could be regulated through the contents of crosslinker, kaolin and acrylamide, the neutralization degree of acrylic acid. Additionally, temperature and ionic strength of release medium may also affect urea release process.The studies combined the slow release fertilizer techniques and superabsorbents, and had significantly theoretical and practical means. The samples may be especially useful in agricultural and horticultural applications in the dry area.