| It is an urgent issue to improve the efficiency of fertilizer utilization, reduce the cost of fertilizer and reduce the pollution of the environment in fertilizer industry. For this reason, development of “environmental-friendly, eco-efficient and low priced” coated slow/controlled released fertilizer is one of the major trends in the current fertilizer industry, and it plays an important role in promoting the construction of ecological civilization.In this paper, the author chose biodegradable starch, polyvinyl alcohol and bentonite as the main raw materials. The author added the cross-linked agent and plasticizer to prepare the coated material, which were used for coating urea to prepare coated urea fertilizers. Simultaneously, the properties of coated materials, slow-releasedproperties and the effect of coated urea were also studied. The main results are as follows:The research involves optimal amount of cross-linked agent in starch/polyvinyl alcohol cross-linked fluid, water absorbent and retention of starch/polyvinyl alcohol/bentonite film material, kinetics and thermodynamics of ammonium ion adsorption, the influence of film materials on p H and seed germination, the test of enzymatic degradation and biodegradation, the observation of biological imaging microscope and FTIR characterization in field etc.The main conclusions are as follows:' The content of amylase in corn starch was higher than in potato starch, corn starch as raw material selection was more appropriate. The author used sodium hydroxide to improve the solubility of corn starch. Formaldehyde and borax together as across-linked agent, the optimal amount of formaldehyde and borax were 1.5 m L and 0.1 g.'Chemical linking was used to make starch/polyvinyl alcohol/bentonite coated films which the bentonite contents was 0, 1.5%, 3.0% and 4.5%, respectively. Fourier transform infrared spectroscopy showed that inthe coated films, polyvinyl alcohol、starch and bentonite induced cross-linked reaction to form hydrogen bonds, and resulted in changes in the structure, but bentonite structural characteristics did not change. Water absorption and retention of coated films changed with the increasing bentonine contents. Kinetics and thermodynamics of ammonium ion adsorption could be described by pseudo-first order kinetics equation, pseudo-second order kinetics equation and Freundlich model, respectively. Ammonium ion adsorption in the coated films was controlled by diffusion step, and it belonged to multilayer chemisorption. And the maximum adsorption capacity increased with increase of bentonite in coated films. Coated films had a certain buffer capacity for the solution with different p H, especially when the p H was 4, 5, 6, the buffer effect was better; In the condition of salinity/alkaline stress, coated films promoted seed germination of mung bean. Compared with alkaline stress, coatedfilms could better promote seed germination of green beans in salt stress; α-amylase and soil microbes degraded the film materials, and the degree of degradation decreased with the increase of bentonite content in coated films.' Coated film which contains bentonite could extend the leaching time of total nitrogen, NH4+-N and NO3--N to improve coated urea fertilizer efficiency.' Compared with urea and coated urea which didn’t contain bentonite, starch/polyvinyl alcohol/bentonite coated urea fertilizers could provide NH4+-N and NO3--N for pakchoi in the growth cycle. Both of slow-released effect was changed with the increase of bentonite content. In addition, because of adequate nitrogen supply in the growth cycle of pakchoi, it improved the effect of nutrients, and the leaf length, leaf width, dry weight and fresh weight of pakchoi all incrased. |
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