Preparation Of Three Novel Acrylamide Hydrogel And Their Application In Tobacco

The uneven distribution and shortage of water resources,land desertification and unreasonable application of fertilizers pose a threat to China’s land resources,affect soil quality and seriously restrict the development of agricultural production in China.As a new environment-friendly material,hydrogel can effectively improve soil quality,improve soil water storage and water retention capacity,improve fertilizer use efficiency,reduce crop diseases and insect pests,and absorb soil heavy metals.It also has the advantages of easy availability,degradability and economical application.at present,hydrogel is widely used in agricultural production.In this study,acrylamide(AM),potassium humate(HAK),sodium carboxymethyl cellulose(CMC),peanut shell biochar(Biochar,B)and modified biochar(Modifiedbiochar,MB)were used as raw materials to prepare hydrogel,and the application experiment of tobacco was carried out.The results are as follows:1.Acrylamide/potassium humate(AM/HAK)hydrogel,acrylamide/sodium carboxymethyl cellulose/biochar hydrogel(AM/CMC/B)and acrylamide/sodium carboxymethyl cellulose/modified biochar hydrogel(AM/CMC/MB)were prepared by cross-linking polymerization.The structures of the hydrogels were characterized and identified by infrared spectroscopy(FT-IR)and scanning electron microscopy(SEM).The results showed that the above three hydrogels were synthesized successfully.2.The water absorption properties of hydrogels were tested.The results showed that the equilibrium swelling degrees of AM/HAK,AM/CMC/B and AM/CMC/MB hydrogels increased by 62.43%,60.78%and 74.83%respectively compared with those of water-retaining agents sold in the market.In addition,the water molecular diffusion processes of the three hydrogels all followed the law of non-Fickian diffusion.The water retention test results of hydrogels show that the water retention rate of AM/HAK,AM/CMC/B and AM/CMC/MB hydrogels can reach 62.38%to 81.25%after being placed at room temperature for 10 hours,and AM/HAK has the best water retention effect.The results of adsorption test showed that the equilibrium adsorption capacities of AM/HAK,AM/CMC/B and AM/CMC/MB hydrogels in different pH Cd2+ solutions were 96.20～152.43,97.83～164.83 and 103.54～164.83 mg·g-1,respectively.When pH=5,the equilibrium adsorption capacity of Cd2+ reached the maximum.The results of adsorption kinetics and adsorption isotherm tests show that the adsorption behavior of three kinds of hydrogels for Cd2+ at different times is more consistent with the quasi-second-order adsorption kinetic model,and in different initial concentrations of Cd2+solution,the adsorption isotherm models of hydrogels follow the Langmuir and Freundlich isotherm adsorption models,and are beneficial to the adsorption of Cd2+.3.The effects of hydrogel AM/CMC(prepared by predecessors)and AM/HAK on the normal development of potted tobacco seedlings were investigated.the results showed that the equilibrium swelling degree of hydrogel AM/CMC and AM/HAK was as high as 26.52 g·g-1 and 31.43 g·g-1.The water retention of two kinds of hydrogels stored at room temperature for 12 hours could reach 68.09%and 79.56%,respectively.After adding hydrogel AM/CMC and AM/HAK,the soil moisture content increased by 2.4%and 3.65%respectively,and the agronomic characters such as plant height,stem circumference and pitch of tobacco were higher than those of the control.SPAD value increased by 4.65%and 10.22%,respectively,and aboveground biomass increased by 23.30%and 52.51%,respectively.The(GS)activity of glutamine synthetase increased by 1.81 μmol(g·h)-1 and 2.12 μmol(g·h)-1,respectively;the glutamate dehydrogenase(GDH)activity increased by 16.78 U·g-1 and 40.45 U·g-1;the root activity of tobacco increased by 31.76%and 63.98%compared with the control;the content of total sugar and potassium increased,while the content of chlorine decreased.Hydrogel AM/HAK can effectively promote the growth and improve the chemical quality of tobacco.4.The effect of hydrogel AM/CMC/B on the growth and development of potted tobacco seedlings under Cd stress was investigated.The results showed that the addition of hydrogel AM/CMC/B could promote the growth of tobacco seedlings under Cd stress.When 10 mg·kg-1 Cd2+was added,AM/CMC/B significantly improved the phenotype of tobacco seedlings and made the roots of tobacco seedlings more developed than the blank control.Compared with the control,the fresh weight of aboveground and underground parts of tobacco seedlings increased by 98.39%,130.67%and 84.22%,231.82%,respectively.The photosynthetic rate and SPAD value of tobacco seedlings increased significantly,stomatal conductance(Gs)and stomatal number increased.AM/CMC/B increased the antioxidant activity of tobacco seedlings,significantly decreased the content of MDA,and decreased the content of Cd in roots,stems and leaves and the cell death rate of leaves.AM/CMC/B hydrogel had the most significant effect on relieving Cd stress of tobacco seedlings.5.The effects of three new hydrogels on the growth and development of potted tobacco seedlings under drought stress were investigated.the results showed that the three new hydrogels could effectively alleviate the drought stress of tobacco seedlings and promote the growth of tobacco seedlings.The modified biochar hydrogel AM/CMC/MB,mainly improved the phenotype of tobacco seedlings under drought stress,and increased the maximum leaf length,maximum leaf width,maximum leaf area,total root length,total root surface area,average root diameter,root tip number and root volume by 49.06%,47.74%,120.38%,69.52%,72.48%,43.65%,81.05%and 150.88%,respectively.The aboveground fresh weight and underground fresh weight of tobacco seedlings increased by 184.32%and 232.54%respectively,and the aboveground dry weight,underground dry weight and relative water content of leaves increased by 192.06%,300.005%and 42.22%respectively.The stomatal opening and SPAD value of tobacco seedlings were increased.The MDA content of tobacco seedlings decreased by 47.50%and the cat and POD activities increased by 198.15%and 198.23%,respectively.Hydrogel AM/CMC/MB could significantly reduce the accumulation of ROS in tobacco seedlings and increase the total amount of 30 metabolites detected by 50.33%.The hydrogel prepared in this study has achieved remarkable results in the application of tobacco,in which AM/HAK is suitable for the normal growth state of tobacco and is beneficial to improve the quality of tobacco leaves;AM/CMC/B is suitable for solving the problems of heavy metal pollution in soil and alleviating heavy metal stress in tobacco;AM/CMC/MB is suitable for drought-resistant cultivation of tobacco to solve the inhibition of tobacco growth and development under drought stress.At the same time,three new types of self-made hydrogels can absorb heavy metal pollutants in water and can also be used to remove heavy metals in sewage.This study laid a certain foundation for drought-resistant cultivation of tobacco and improvement of soil quality of tobacco planting,and has a broad application prospect in agricultural production.