Preparation And Application Of The Polyvinyl Alcohol/Diatomite Composite Coated Slow-release Potassium Fertilizer

Compared with ordinary instant fertilizers,slow-release fertilizer can control the slow release of fertilizer nutrients in the soil,meet the demand for nutrients within the crop growth cycle,increase the yield and quality of crops,and significantly increase the fertilizer utilization rate.The reduction in the amount of fertilizer usage reduces the waste of resources and soil pollution.Accordingly,slow-release fertilizer is the direction of fertilizer development in the future.It is a common problem in most coated slow-release fertilizers currently on the market that the coating layer is difficult to degrade.With the growing awareness of environmental protection,the degradable coating materials have become a research hotspot.In this paper,a low-cost,non-polluting,long-acting polyvinyl alcohol?PVA?/diatomite coated slow-release potassium fertilizer was prepared by selecting organic and inorganic coating materials,determining the cross-linking agent,and designing the process.The surface morphology of the slow-release potassium fertilizer before and after nutrient release was observed by scanning electron microscopy?SEM?.The compressive strength of the slow-release potassium fertilizer was tested using a particle strength tester.Water dissolution rate and soil dissolution rate of slow-release potassium fertilizer were used to investigate the release performance,and it was applied in tobacco cultivation.The results are shown as follows:1)The PVA/diatomite coated slow-release potassium fertilizer was prepared using a rotary spray method.The binder PVA solution concentration is 2%,the crosslinker borax solution concentration is 3%,and its optimal formula is K₂SO₄:diatomite:cement:polyvinyl alcohol:borax:cellulose acetate=80:10:6.5:3.2:0.1:0.2.2)The compressive properties of the coated slow-release potassium fertilizer increase with the increase of the thickness of the coating film and the amount of the hydraulic binder.The hydraulic binder can effectively improve the water resistance of the slow-release potassium fertilizer and can act as a sealant to fill the pores of the membrane to prevent the entry of water molecules.3)The sustained-release characteristics of coated slow-release potassium fertilizers increase with the increase of coating thickness.7-day water-dissolving experiments showed that 20%coated slow-release potassium fertilizer had the highest rate of nutrient release on the fourth day.Soil dissolution experiments showed that the sustained-release of potassium fertilizer began to release nutrients in the soil after20 days in the soil.The sustained-release period can reach 80 days,and the sustained-release performance is excellent.The polymer shell formed after PVA cross-linking makes the nutrient release of the fertilizer appear delayed period and constant release period.4)The coated slow-release potassium fertilizer was applied to tobacco cultivation.Results showed that the sustained-release potassium fertilizer has the same nutrient release characteristics as the tobacco requires fertilizer,so as to show the effect of promoting the growth of tobacco leaves.The 20%coated slow-release potassium fertilizer has excellent sustained-release properties,and the nutrient release rate in the field is basically consistent with the requirement of tobacco leaf fertilizer.After 30 days of tobacco planting,the growth of tobacco leaves is significantly promoted.When the amount of potassium is 20%,the content of nicotine in tobacco leaves can be effectively reduced,the potassium content in the middle leaves can be increased by 21.6%,and the potassium content in the upper leaves can be increased by 36.3%.5)Coated slow-release potassium fertilizer preparation process is simple and easy,can be carried out under normal temperature and pressure.The material cost accounting is only about 2800 yuan/ton,lower than the price of K₂SO₄,less than 1/2of the market price of slow-release potash fertilizer,which is a clear advantage in price.