Preparation Of Sustained-release Potassium Fertilizer With Carrier Of Bentonite And Study On Its Sustained-release Characteristics

According to the study, the seasonal utilization of the fertilizer in ourcountry is very low, with nitrogen about30%³5%, phosphate10%²0%,and potassium35%⁵0%[1]. Low utilization not only causes a huge waste ofresources, but also brings about serious environmental pollution. To welladdress this problem, many countries are competing for research anddevelopment of various slow release fertilizers. However, most studies havefocused on nitrogen and phosphorus, few studies given to potassium[2].Among the17necessary elements for the crop growth, potassium is in thethird place, who participates in various important physiological activities inthe plants. It is the cofactor of more than40enzymes, can promote theprocess of respiration and the formation of nucleic acids and proteins, andaffects the synthesis and transport of the sugar[3]. Potassium deficiency cancause leaf cells dehydration, protein disintegration and chlorophyll damage,thus inhibiting the plant growth, affecting the absorption of N, P and othernutrients, and finally resulting in lower utilization of fertilizers[4]. In the lightof China’s agricultural development plan, in the early21st century our countryneeds at least5.32million ton K₂O. But the actual output of potash fertilizeraccount for only50%of the demand[5]. The ratio of N, P and K has been outof tune for a long time, especially the potassium, thus resulting in the lessstudy on slow or controlled release fertilizer for potassium.With natural, cheap and porous mineral bentonite as the carrier of rawpotassium fertilizer K2SO4, the research then add some urea-formaldehyderesin to bond and mix them. With the help of electric pressure machine, theslow release potassium fertilizer was well made.Through the method of water dissolution rate, the sand column leachingsolution, soil column leaching test and potted plants experiment, the paper then gave a preliminary study on the sustained release effect of the aboveself-made slow release fertilizer. The main conclusions were as follows:（1） With the cumulative release of potassium in the water dissolution rate,the sand column leaching and soil column leaching method as the investigatedindicators, and from the perspective of a single factor analysis, the articleexplored the influence of the type of bentonite, the amount ofurea-formaldehyde resin, the rate of soil and fertilizer on the nutrient releaseproperties of the prepared slow release fertilizer tablets:①The type of bentonite has some certain impact on the tablets’nutrient release properties. Both the water dissolution rate method, sand andsoil column leaching method all showed the same nutrient release trend,which were that the sodium bentonite were the best, followed bypotassium-based soil, and calcium bentonite worst. But the difference amongthem was not significant.②The amount of urea-formaldehyde resin has great influence on thetablets’ nutrient release properties. The basic trend was that the cumulative Krelease rate increased with the amount of resin decreases. But when theamount of resin increased to a certain extent, this difference was not apparent.Take the water dissolution rate method for example. The cumulative releaserate of potassium in28days of the tablets with5%resin was the largest one,which arrives at62.13%, while the tablets with20%resin and25%resin were29.54%and27.85%respectively.③With the decrease of the ratio between soil and fertilizer, thepotassium’s cumulative release rate showed an increasing trend. That was tosay, the greater the proportion of soil was, a better nutrients releaseperformance it would have, accordingly it would have higher effectiveutilization of nutrients. When the slow release fertilizer was soaked in the25℃water for28days, the cumulative release rate of potassium showed that the rate of soil and fertilizer which was10:8has the maximum value of45.83%, while the10:2fertilizer was the smallest33.05%.（2） Through single factors effect analysis, the article brought forward thebest slow release fertilizer preparation process: sodium bentonite,20%urea-formaldehyde resin （of total fertility weight）, soil and fertilizer ratio10:2. Under these conditions, the self-made fertilizer’s initial dissolution rate inthe water was19.74%, and its cumulative nutrient release rate in28days was31.63%.（3） On the basis of the above analysis, the paper then explored thenutrient release mechanism of the self-made slow-release fertilizer tablets:Bentonite with multi-lamellar structure has physical adsorption for K+, whichdepends on the bentonite’s property such as cation exchange, adsorption andadhesion. After the addition of urea-formaldehyde resin, with its cementationand solidification, layers of protective film surrounding the bentonite carrierfertilizer was formed. Thus there was a certain degree of polarity between thenearby K and membrane material’s molecules, so that the nutrients would noteasily be released into the outside environment.（4） By comparison of the plant height, stem circumference, number ofleaves under different fertilizer treatments, we found that the self-made slowrelease fertilizer could improve the tomatoes’ agronomic traits （plant height,stem circumference and leaf number）.But further observation was needed.