| Experiments of screening, compounding, and modifying easily degradable material suchas vegetable oil and weathered coal were conducted to study film-forming properties,microstructure, and nutrient release characteristics of SCRF. Experiments of nutrient releaseunder different conditions and efficiency test about several crops were conducted to discussnutrient release characteristics of SCRF and fertilizer formulations on field crops. The resultswere as follows:1. There was a certain relationship between stated release time of vegetable oil coatedurea and its nutrient release curve. The nutrient release curves were parabola pattern forcoated urea with shorter release time,"S" pattern for coated urea with longer release time, andlinear pattern for other coated urea. The nutrient release characteristics of vegetable oil coatedcompound fertilizer were similar to the power multiplication function curve. The nitrogenrelease rate of coated compound fertilizer was the fast, next was potassium, and phosphorusrelease rate was the slowest. Nutrient release dynamics characteristics could be describedusing the linear regression equation and the polynomial equation. Vegetable oil thermalcrosslinking reaction showed that curing reaction of vegetable oil speeded up with thereaction temperature. The effect of T6was the best of all the treatments. The effect of T3maybe better than that of T6in the process which fertilizers were coated. Microstructure analysisshowed that the inner surface of the vegetable oil coated urea was a whole formation, but theinner surface of the film had a lot of coral shaped bulges. The external surface of the film wassmooth. There were a small amount of smooth bulge and micropore. The fracture of the filmwas smooth and sleek. The film was without distinct boundaries and serried. The film was nota homogeneous system, so that surface of the film was irregular surfaces.2. By measuring the nutrient release characteristics of slow/controlled release fertilizers,the results showed that production made under the temperature of70℃and80℃was betterin controlling nutrient release. The bigger the particle size of weathered coal was, the worsethe performance of fertilizer was. The binder VS humic acid (B/H) ratio with biger value hadbetter effect on the nutrient release performance of fertilizers. Contribution rate of binder wasmore than that of weathered coal in controlling nutrient release. Microstructure analysisshowed that the film consisted of two layers. One was the rough layer which was constitutedby weathered coal; another was the dense layer which was constituted by a special binder. Inner surface of the film covered with a large number of gaps. External surface of the filmappeared cascade-like distribution. Many micropore and particulate matter were scatteredover external surface of the film.3. UF was slow-release nitrogen fertilizers by chemical synthesis. Through studyingurea-formaldehyde binder, urea-formaldehyde compound fertilizers were got as new slowrelease fertilizer, combined with manufacturing technique of compound fertilizer. Theinvestment was low for process equipment, and technology is very mature. Using existingfertilizer production line, the cost of production was significantly reduced in comparison withsimilar products. These advantages benefited urea-formaldehyde fertilizers to be rapidlypopularized for agricultural production.4. The release curve of SCU, PSCU, and MSCU were similar to the "L" shape whichrotated90degree. The order of nutrient release rate was SCU＞PSCU＞MSCU. The nutrientrelease characteristics of modified sulfur coated urea were similar to the power multiplicationfunction curve. The anti-collision and friction effect of MSCU was the best of all thetreatments. Debris of MSCU was0.46times more than that of PSCU, and was0.07timesmore than that of SCU. The difference among the three groups was statistic ally significant(P<0.05). It was viable that sulfur coated urea was resined to improve the brittleness of sulfurfilm. Arrange and deposit of sectional material were relatively compactness. The sulfur filmconsisted of three layers which were scatter layer and dense layer. There were a large numberof intensive wrinkle on the inner surface and small pearl-like grains on the external surface.The modified sulfur film consisted of two layers which were resin layer and sulfur layer.5. The rapid method could be used to determine nutrient release rate and stated releasetime. Therefore, different batches of slow/controlled release fertilizers could accuratelydetermine stated release time. By rapid measuring method predicted nutrient release period,only CRF13met the25%upper limit of allowable error of12samples. When conditions suchas envelope materials, additives and spraying temperature were changed, the evaluation ofslow/controlled release fertilizers was not reliable with the original prediction equation. Therapid prediction equation needed to be obtained according to making mathematical statisticsafresh.The release rate of controlled release fertilizer fluctuated with the decrease of theextraction temperature. The stated release longevity of CRF1and CRF2at15℃wererespectively1.5times and1.67times than those at25℃. The stated release longevity ofCRF1and CRF2at5℃were both2times than those at25℃. Effects of lower thetemperature on stated release time of controlled release urea had weakened. The nutrient release curve in spring was "J" pattern and a diagonal pattern in summer. The test of soilwater content on the nutrient release rate of the SCRF showed that50%was the critical valueof soil relative water content which did not affect the nutrient release rate of the SCRF in soil.6. Yield of the rice increased significantly when application of fertilizer was more than50%level of total nitrogen. The difference of rice yield was not statistic ally significant whenapplication of fertilizer was more than70%level of total nitrogen. The order ofyield-increasing effect was CRU70%＞CRU100%＞CRU50%. Yield with70%treatment wasthe highest. The order of rice yield was CRU70%＋PU30%＞CRU50%＋PU50%＞CRU42%＋PU28%＞PU100%＞CRU70%＞CK about mixture ratio between CRU and PU. ApplyingPSCU not only controlled nutrient release rate but also applied elemental sulfur by reason oftwo films, So that yield with PSCU treatment was the highest among four kinds of fertilizers. |
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