Preparation And Properties Of Starch-Based Slow- And Controlled-Release Fertilizer

Similar to humans and animals,plants also need nutrients to promote their growth and development.Fertilizer is a chemical added to soil,which can directly or indirectly provide nutrients for plants to increase crop yields.In recent years,the global population has been rising.In order to meet the food demand of the world population and to solve the problem of food security through sustainable agriculture,fertilizer is widely used.However,up to now,most of the traditional chemical fertilizers have caused a lot of nutrients loss,low efficiency of nutrient absorption by plants,and serious loss of farmland resources,due to mineralization,leaching and volatilization.In addition,the lost nutrients increased the burden on the environment,and caused risks and pollution.In order to solve this problem,slow and controlled release fertilizers have been widely researched.These fertilizers can encapsulate nutrients effectively,meet the specific plant nutritional requirements of different plant growth stages with minimal nutrient loss,and provide targeted and controllable nutrients for crops,which can significantly increase crop yield under specific soil conditions.In recent years,people pay close attention to environmental protection,human health and so on,because a series of environmental problems such as air pollution,land desertification and soil erosion have emerged.Green and environmentally friendly slow-and controlled-release fertilizers have become the hot points of attention of scientists.Starch,a common natural polymer,is an ideal material for the preparation of degradable and controlled-release fertilizers,which has many advantages in nature,such as wide source,good price,safety and environmental protection.Starch molecules are formed by connecting the glycoside bonds between the alpha-D-glucose and contain a large number of hydroxyl functional groups.Starch can be modified to have an ideal performance.In this dissertation,the starch molecules were modified,and the modified starch was used as the raw material to synthesize three novel types of slow-and controlled-release fertilizers.The slow release behavior of the three fertilizers was studied.The specific research contents and conclusions are as follows:1.Carboxymethyl starch was prepared using isopropanol.Carboxymethyl starch hydrogel was prepared using potassium persulfate as an initiator,N,N-methylene diacrylamide as a crosslinker,by grafting acrylic acid and 2 acrylamide-2-methyl propylpropane acid to carboxymethyl starch.A double coated slow release nitrogen fertilizer was prepared using urea particles as the fertilizer kernel,ethyl cellulose as the inner coating,and carboxymethyl cellulose hydrogel as the outer layer.The experimental results showed that the water absorption of the carboxymethyl starch hydrogel in tap water can reach 298 g/g.The soil moisture can be improved by applying in acid soil and alkaline soil,and the water retention capacity of the soil can be improved effectively.The slow release behavior of fertilizers in two soils showed that the fertilizers could slow down the release of urea and have certain slow release ability.In addition,the degradation experiments in acid soil and alkaline soil showed that the outer carboxymethyl starch hydrogel had good degradation ability.2.Carboxymethyl starch and dialdehyde starch were prepared by corn starch,and two kinds of leaf potash fertilizers were prepared by reaction with dibenzo-18-Crown-6-ether,respectively.The performance of two kinds of foliar potash fertilizer was studied by elemental analysis and inductively coupled plasma.Slow release behavior of two kinds of foliar potash fertilizer was studied in different pH value solutions.The experimental results showed that two kinds of fertilizers can release nutrients slowly.The dialdehyde starch leaf potassium fertilizer has pH sensitivity by introducing the dynamic Schiff base bonds.It can regulate nutrient release according to different pH environment.Carboxymethyl starch foliar potassium can not be influenced by the environmental pH value,and release potassium ions for a long time.Pot experiment results showed that two kinds of fertilizers could promote the growth of soybean seedlings.3.The porous carboxymethyl starch was prepared by enzymatic hydrolysis,and used to adsorb iron nitrate.Montmorillonite was coated on the starch by ion exchange to prepare a kind of nano iron fertilizer.The sustained release properties of the nano iron fertilizer were investigated.Scanning electron microscope images showed that the porous carboxymethyl starch hydrolyzed by enzyme had porous structure and the size of pores was homogeneous.Porous carboxymethyl starch has excellent adsorption properties and can adsorb a large number of iron ions.The nutrient release behavior of the prepared nanoscale iron fertilizer was studied in different pH solutions and different soils.The results showed that the fertilizer had certain slow release ability under different pH conditions.