Study On The Manufacture Of Environmental-Friendly Coated And Slow-Release Fertilizer And Its Nutrient Control And Release Mechanism

The production and use of environmental-friendly of coated and slow-release fertilizerwas one of the main trends for the development of chemical fertilizer industry at present, andwas necessary need for the development of modem agriculture and sustainable developmentstratagem. With the view to the exploitation of coated and slow-release fertilizer of highefficiency, environmental protection and low cost, environmental-friendly, price-lowpolyvinyl alcohol-starch combination liquid and source-broad diatomite (or zeolite powder)complex were selected as coated materials for granular fertilizer in this article. Drum technicswas used to produce coated and slow-release fertilizer. The fertilization effect of keep andcontrol of organic-inorganic complex coated and slow-release fertilizer, nutrientcontrol-release mechanism were studied systematically, the contents involved the choice ofwater resistance of membrane materials and the agreeable dosage of organic high molecularcomposite, nutrient control-releasing mechanism of fertilizers after coating,environmental-friendly and application effect in field etc. The main results were as follows:1. Formaldehyde, borax and urea could increase water resistance of polyvinyl alcohol-starch combination liquid. The lowest water absorption rate of membrane was modified byurea, and it was more fit as modifier to increase the water resistance of polyvinyl alcohol-starch combination liquid.2. The results of soil column leaching experiment indicated, when the proportion ofmembrane material and the amount of fertilizers was given, the nutrient slow-release effect ofcoated fertilizer which mixed and made by polyvinyl alcohol-starch combination liquidmodified by urea and diatomite (or zeolite powder) was the best, the proper proportion of twomaterials was found in this article.3. Nitrogen leaching process of coated and slow-release urea could described byfirst-order reaction kinetics equation (N,=N₀[1-exp(-kt)]).The leaching constant kincreased with temperatures increment, soil water contents increase and the increasing ofwater vapor pressures. The differences of inside and outside water vapor pressures were thedirect reason for the nutrient leaching. And temperatures, soil water content etc. could affectthe nutrient leaching rate by changed the differences of inside and outside water vaporpressures. 4. Scanning electron microscope test indicated, the structure of film forming of granularfertilizer surface was different with the membrane materials. Film forming mixed bypolyvinyl alcohol-starch combination liquid and diatomite was sheet while the polyvinylalcohol-starch combination liquid and zeolite powder was flocculent and had many smallholes, it was the reason for the difference of the nutrient slow-release effect caused bydifferent membrane materials. Compared with the infrared spectrogram of before and afterurea grains coated by the mixed material of polyvinyl alcohol-starch combination liquidmodified by urea and diatomite, new chemical bond was formed between membrane andgranular urea and the binding power was strong, which helped to enhance the slow-releasecapability of urea.5. The coated and slow-release urea could inhibit volatilization of nitrogen, comparedwith the control treatment. The effect of nitrogen inhibition was better in the treatment ofpolyvinyl alcohol-starch combination liquid and diatomite than polyvinyl alcohol-starchcombination liquid and zeolite powder. The membrane of coated material could bedecomposed naturally. Capsicum fertilizer efficiency experiment indicated coated urea couldincrease capsicum yields, content of NO₃^--N decreased and increase the utilization rate offertilizer compared with the routine urea.In conclusion, the combinated material of modified polyvinyl alcohol liquid anddiatomite(or zeolite powder) could be used as coated membrane material of fertilizers with agiven proportion. The fertilizer with the above coated membrane showed advantages of lowcost, stable nutrient leaching and non-pollution to soil. Diatomite was an advisable andrecommendable coated membrane material compared with zeolite powder.