Preparation And Performance Study Of Water-absorbing And Water-retaining Biochar-based Slow-release Fertilize

Water and fertilizers are two essential elements in the process of crops growth.The combination of superabsorbent polymer and fertilizers can produce absorbent and water-retaining slow-release fertilizers.However,the traditional superabsorbent polymers are mainly prepared with synthetic materials,which have disadvantages such as high production cost and poor degradation performance.Carbon materials have been widely used in the preparation of carbon-based slow-release fertilizers due to their large surface area,porous structure,abundant functional groups and the ability to improve soil properties.But it has some problems such as poor water absorption and retention performance.In order to solve the above problems,this paper firstly takes corn straw cellulose extracted from corn straw as raw material,and then grafts it with polyacrylic acid or poly（acrylic acid-potassium humate）to prepare degradable superabsorbent polymer and water absorbing and water-retaining slow-release fertilizers,respectively.Secondly,the modified corn straw carbon was prepared by activating and pyrolyzing corn straw.Then the nutrient was loaded onto the modified corn straw charcoal to prepare slow-release fertilizer.Finally,the straw carbon base fertilizer was introduced into the superabsorbent polymer to prepare the water absorption and water-retention corn straw carbon slow-release fertilizer.The main research contents and results are as follows:（1）The superabsorbent polymer（CSC-g-PAA）was prepared by solution polymerization of CSC and acrylic acid（AA）monomer.The water absorption rate of CSC-g-PAA in deionized water can reach 702.89 g/g.After five cycles,the water absorptivities of CSC-g-PAA in deionized water was 47.27%of their initial water absorption,indicating that CSC-g-PAA had repeated water absorption.Adding CSC-g-PAA to the soil can enhance the soil’s water-holding and water retention capacity.The degradation rate of CSC-g-PAA was 24.14%after 50 days in soil,showing good degradation performance.（2）Using potassium humate（KHA）as nutrient,corn straw cellulose grafted poly（acrylic acid-potassium humate）（CSC-g-P（AA-KHA））was prepared by solution polymerization.The water absorption rates of product prepared are 792.89 g/g and 72.69 g/g in deionized water and 0.9 wt%Na Cl solution,respectively.After five cycles,the water absorptivities of CSC-g-P（AA-KHA）in deionized water and 0.9 wt%Na Cl solution were51.71%and 49.97%of their initial water absorption,respectively.Adding CSC-g-P（AA-KHA）to the soil can be found to have a better water holding and water retention capacity than adding CSC-g-PAA to the soil.The degradation rate of CSC-g-P（AA-KHA）was 32.02%after 50 days.Soil column leaching test and pot experiment demonstrated that the release rate of KHA from CSC-g-P（AA-KHA）has been delayed and CSC-g-P（AA-KHA）had significantly promoted the growth of maize plants,respectively.（3）Firstly,Corn straw carbon（CSAC）was obtained from corn straw by activation and pyrolysis,and then the corn straw carbon based slow-release fertilizer（P-CSAC）was obtained by saturated adsorption of phosphate solution.Finally,the water-absorbing and water-retaining corn straw slow-release fertilizer（P-CSAC@CSC-g-PAA）was prepared by in-situ polymerization with CSC and AA.The preparation conditions of CSAC are:500℃,1 mol/L Mg Cl₂·6H₂O and 90 min.The adsorption kinetics showed that the adsorption of phosphate by CSAC was chemisorption.The isothermal adsorption curve further indicates that the adsorption of phosphate on CSAC is an adsorption process involving surface precipitation.It mainly involves precipitation,electrostatic attraction and surface functional groups,among which precipitation is the most critical.The cumulative sustained release rates of P on day 1,day 7and day 32 of P-CSAC@CSC-g-PAA supplemented with 6 wt%of P-CSAC were 0.65%,6.77%and 24.68%,respectively.In conclusion,this paper uses low-cost agricultural waste as the main raw material to successfully prepare functional fertilizers that collect water absorption,water-retention and slow-release of nutrients,which has the potential to improve the utilization rate of water resources,reduce fertilizer loss and environmental pollution.