Preparation Of Sodium Alginate-based Slow-release Materials And Their Soil Improvement Performance

In recent years,with the rapid development of agriculture,soil degradation has become a major global problem.In this context,effective soil improvement has become the most important means to solve soil problems.The application of soil conditioners can effectively improve the physical and chemical properties of soil,but conventional soil conditioners have the disadvantages of complex preparation process,high preparation cost,inability to respond to the external environment,difficulty in degradation and harmful to the environment.Therefore,it is important to prepare a new soil conditioner with slow-release function to improve soil physical and chemical properties and ensure sustainable agricultural development.In view of this,this paper prepares gel slow-release microspheres loaded with humic acid（HA）by drop-injection method using sodium alginate（SA）as carrier,and enhances its slow-release performance by compounding with charcoal（C）and chitosan（CS）,which provides a low-cost and simple preparation method to enhance the utilization efficiency and extend the use time of SA-based soil improver,and has potential applications in practical applications.It has potential applications in practical applications.In this paper,SA@HA gel spheres were prepared by drop-in method using SA and HA as raw materials.The physical and chemical structures were characterized by modern analytical methods such as SEM and FTIR,and their slow-release properties and soil improvement properties were discussed in detail.The results showed that the gel spheres were uniform in size,with diameters of about 1～2 mm,and their interiors showed a three-dimensional mesh structure.The slow-release experiments showed that the gel spheres produced an obvious"sudden release"phenomenon in the first 20 h.When the p H value of the solution increased from 4.0 to 10.0,the cumulative release of HA increased from 29.01%to 80.27%in 20 h,and gradually reached the slow-release equilibrium at 80 h.The soil experiments showed that SA@HA was released in the first 20 h.Soil experiments showed that the maximum water holding capacity of laterite,plantation soil and saline soil increased by 14.07%,16.86%and11.62%under SA@HA gel sphere treatment,respectively.After 50 d of restoration,there were increases of 18.48～50.76 mg/kg and 29.96～78.91 mg/kg of effective phosphorus and fast-acting potassium in the three soils,respectively,indicating that SA@HA gel balls can effectively improve the water-holding properties and soil physicochemical properties.Compared with the blank control,the plant height of maize and pakchoi treated by SA@HA gel ball increased by 2.16 cm and 0.63 cm,respectively.In conclusion,SA@HA gel spheres have potential value and wide application in soil improvement and crop growth promotion.To improve the problem of"sudden release"of SA@HA gel spheres,this paper compounded SA/AC@HA gel spheres with activated C（AC）as an additive,and C can not only improve the fixation of SA-based gel spheres to the amendment,but also reduce the"sudden release",and can be used as an effective soil amendment to improve the physical and chemical properties."The incorporation of C not only improves the fixation of SA-based gel spheres to the amendment,but also improves the physical and chemical properties of soil as a soil amendment.The effect of the ratio of SA,AC and Ca Cl₂ on the slow-release performance of the gel spheres was investigated using orthogonal experiments,and the physical and chemical structures were characterized by SEM,FTIR and XRD,and the soil amelioration performance was discussed in detail.The results showed that when the ratio of KOH to C was1:1,AC had a large comparative area and average pore size,with a specific surface area of2673.53 m²/g and an average pore size of 3.76 nm.The results of the slow-release performance measurement showed that the gel spheres prepared with the mass ratio of SA,AC and Ca Cl2 of1.5:1:5 had the best slow-release performance.The release of HA in alkaline buffer solution at p H 10.0 was 40.65%at 20 h,indicating that the addition of AC effectively slowed down the sudden release of HA.The cumulative release of HA increased from 31.89%to 92.19%when the solution p H was increased from 4.0 to 10.0,indicating that SA/AC@HA gel spheres had good p H responsiveness and tended to be completely released under alkaline conditions.The results of soil improvement experiments showed that after 50 d of remediation,the NH₄⁺-N in the three soils did not change much,and the contents of effective phosphorus,fast-acting potassium and organic matter increased by 34.85～64.55 mg/kg,70.43～81 mg/kg and 2.61～30.27 g/kg,respectively.The planting tests showed that SA/AC@HA gel pellets promoted the growth of both maize and chard,and could provide nutrients for the growth of the crops continuously.In order to give SA/AC@HA gel spheres better slow-release performance,the paper prepared SA/CS/AC（P-（SA/CS/AC）_n）slow-release membranes by layer self-assembly method.The effect of AC addition on the mechanical properties of the membranes was investigated,and the physical and chemical structures were characterized by modern analytical methods such as SEM and FTIR,and their slow-release properties and soil improvement properties were discussed in detail.The experimental results showed that the addition of 1%AC resulted in better mechanical properties of the slow-release membrane.The slow-release results showed that the cumulative release of HA increased from 19.87%to 66.72%with the increase of p H from 4.0 to 10.0 after 700 h.Its slow-release time with the same release amount was about 6times longer than that of SA/AC@HA gel spheres.Soil experiments showed that P-（SA/CS/AC）_n slow-release film could effectively regulate soil p H and increase soil nutrient and organic matter content.Meanwhile,planting experiments showed that the ammonium N,effective phosphorus,fast-acting potassium and organic matter contents in the three soils increased by 2.91～28.62 mg/kg,46.97～70.43 mg/kg,55.89～77.01 mg/kg and 12.47～22.5g/kg,respectively,after 50 d of restoration.planting experiments showed that P-（SA/CS/AC）_neffectively promoted The planting experiments showed that P-（SA/CS/AC）_n effectively promoted the root growth of crops.In summary,the potential of P-（SA/CS/AC）_n in the application of slow release,soil remediation and crop growth promotion has been verified,providing a new direction for soil treatment.