Research On Slow-release Properties Of Starch-based Fertilizer

Starch is a natural polymer organic compound formed by plants through photosynthesis, which is a readily available raw materials, cheap, green and renewable resource. Starch contains more carbon chain and a hydroxyl group structure, and easy to be modified by functional group transformation modified. Although starch and its derivatives have been widely studied and promoted in the biopharmaceutical industry, sewage treatment and fast moving consumer goods and many other areas, while rarely used in the slow/controlled release fertilizers fields. With the increasing public concern towards human health, environmental protection, and natural resource sustainability, it has become important trend for the fertilizer industry to development efficient, simple process, environmentally friendly, low cost multifunctional slow/controlled release fertilizers. In thisstudy, three novel slow-release fertilizers were prepared by physical crosslinking and phase transfer methods using conventional urea, potassium dihydrogen phosphateas nutrients, and starch derivatives, sodium alginate, polylactic acid, etc., as excipients or coating materials. The novel polymer-based fertilizers were characterized by element analysis, atomic absorption, FT-IR and SEM technologies. The slow release properties of the fertilizers were investigated by the solution rate, embedding experiments and pots planting, respectively. The main results are as follows:1. A new DAS-Cys-based slow-release copper fertilizer was prepared by the condensation reaction of L-Cysteine with dialdehyde starch and the followed adsorption process on Cu2+, as well as the followed granulation using sodium alginate. The C, H, N, S and Cu contents in the fertilizer were 28.61%, 4.81%, 3.03%, 6.06% and 3.03%, respectively. This fertilizer showed good slow-release behavior. It was found that only 17.66% of copper of the fertilizer was released in the soil after 28 days. It was confirmed that the copper release was mainly depended on the degradation of the fertilizer. In fact, the successful grafting reaction of L-Cysteine with starch materials and the followed adsorption process on Cu2+ not only can effectively control the nutrient release rate but also can avoid the environmental pollution.2. A slow-release starch-based NPK-Cu compound fertilizer with double coating was successfully prepared via using urea, potassium dihydrogen phosphate and potassium chloride wrapped in urea particle surfaceas kernel, the slow-release copper fertilizer and polylactic acid as the inner coating and outer coating, respectively. The nutrients contentsin this fertilizer were N(15.43%), P(15.85%), K(9.83%), Cu(0.16%). It was revealed that the N(69.79%), P(59.64%), K(48.67%), Cu(16.82%) of nutrients of the fertilizer were released in the soil after 30 days. Thus, this fertilizer obviously hold good slow-release characteristic. The introduction of starch derivative and polylactic acid polymer materials can reduce the cost of the sample and be completely degraded in the soil. At the same time, thses natural polymers can be significantly controlled the release rate of various nutrients in the soil.3. A new slow-release sodium alginate-based zinc fertilizer focused on the process simple, low price, environmentally friendly characteristics, was prepared by using the slightly soluble znic asmmonium phosphate synthesized by zinc sulfate and diammomium phosphate as the main componentand entrapped in the crosslinked sodium alginate. The results showed that the Zn content in the fertilizer was 29.79% and only 19.01% of zinc was released in the soil after 60 days, implying the excellent slow-release performance. It was also found that the zinc release was related to the dissolution of Zn NH4PO4. In this fertilizer, the presence of natural sodium alginate helpedthe granulation of thezinc fertilizer, and effectively improves the environment quality avoids the pollution of the environment.