Creation Of A New Slow-Release Nitrogen Fertilizer Based On Rice Straw Cellulose And Its Mechanism

As a kind of agricultural waste,rice straw occupies an important position in the production and agricultural waste treatment in China.However,due to the lack of effective disposal methods,rice straw is usually burned or landfilled,resulting in waste of resources and environmental pollution.According to statistics,the annual production of rice straw worldwide exceeds 100 million tons.Under such circumstances,it is of great economic,environmental and social significance to efficiently utilize the renewable resources in rice straw and convert them into useful energy or materials.Therefore,the purpose of this paper is to investigate how to efficiently extract cellulose from rice straw,chemically transform it and explore the optimal transformation conditions.A series of performance tests were conducted to analyze the slow-release performance of the transformation products in still water and biodegradability in soil.In terms of application,a pot experiment of urea-loaded slow-release fertilizer based on rice straw cellulose was conducted to investigate the effect of slow-release fertilizer modified by rice straw cellulose on wheat growth.The main results obtained in this paper are as follows:（1）The acid-base extraction method was used to extract cellulose from rice straw,and the extraction process of rice straw cellulose was optimized using single-factor experiment and response surface design method.The results showed that the optimal process conditions for the extraction of cellulose from rice straw were:the mass fraction of Na OH was 4%,the mass fraction of H₂O₂ was 2%,the material-liquid ratio was 1:45（g/m L）,the water bath temperature during the alkali treatment was 70°C,and the water bath time was 0.5 h.The yield of cellulose was 95.73%under these conditions,the crystalline structure of cellulose was type I,the relative crystallinity increased by 31.2%,the thermal stability of cellulose was high,and the main weight loss peak was located at 340℃.（2）The rice straw cellulose was modified by etherification using ethyl bromide as an etherifying agent to prepare ethyl cellulose.The best conditions for the preparation of ethyl cellulose were obtained as follows:toluene was used as diluent,the etherification time was12 h,the etherification temperature was 120℃,and the amount of ethyl bromide was 3times of the cellulose mass.The yield of ethyl cellulose prepared under these conditions was 79.6%,and the degree of substitution ranged from 2.0 to 2.5.Ethyl cellulose was dissolved in ethanol to produce ethyl cellulose-ethanol films with different concentration contents,which are usually biodegradable in soil.The ethyl cellulose-ethanol solution was used as a coating material to cover the surface of the fertilizer granules uniformly to obtain the film-coated urea fertilizer.The initial nitrogen release rate of the film-coated urea fertilizer in still water was 6.84%,and the 28-d accumulated nitrogen release rate was65.46%,which met the standard of nutrient leaching in still water solution in<slow-release fertilizer>（GB/T 23348-2009）.The nitrogen leaching rate of the wrapped urea fertilizer was 56.5%after 5 weeks of leaching in the soil.The results showed that ethyl cellulose-ethanol film is a green coating material for film-coated slow-release fertilizer.（3）Rice straw cellulose based hydrogel（RSC-g-PAA/PVA hydrogel）was synthesized by using free radical copolymerization method with acrylic acid as the monomer,and urea was added during the synthesis of RSC-g-PAA/PVA hydrogel to synthesize rice straw cellulose based urea loaded slow release fertilizer（RP-U-SRF）.The water absorption capacity,slow release capacity in still water,water retention capacity in soil and degradation capacity of RP-U-SRF were tested,and it was concluded that the maximum water absorption multiple of RP-U-SRF was 110 g/g.In still water,the nutrients in RP-U-SRF would be released within 2 h.The water retention capacity of RP-U-SRF in soil was increased by 6.21%compared with that without any addition.increased by 6.21%and its mass degraded by 24.62%in 60 d.Finally,RP-U-SRF was planted in wheat pots and the experimental results showed that after 7 weeks of wheat planting,the height of wheat in the RP-U-SRF group was 33.7cm,dry matter mass was 0.0214 g/plant,and nitrate nitrogen content was 0.0316 mg/kg;the height of wheat in the pure urea F group was 31.4 cm,dry matter mass was 0.0208g/plant,and nitrate nitrogen content was 0.0283 mg/kg.The results showed that the direct application of RP-U-SRF in the soil could effectively promote the growth of wheat plants,and the promotion effect was better than that of common urea fertilizer.In conclusion,RP-U-SRF is a slow-release fertilizer with excellent water absorption and water retention capacity.In this study,by efficiently extracting and converting cellulose from rice straw,we prepared a coating material with biodegradability,which can be used as a coating type slow-release fertilizer and a high water retention slow-release fertilizer that can be biodegraded.It solves the problem of agricultural waste disposal and provides high value utilization of agricultural waste.At the same time,this utilization is in line with the current development trend of slow-release fertilizers and can make a certain contribution to the development of slow-release fertilizers,which has important economic,environmental and social significance.