Preparation Of Slow-controlled Release Nitrogen Fertilizer With Industrial Alkali Lignin And Study On Its Slow-controlled Release Characteristics

As the main direction of future fertilizer development,slow-release fertilizer will play an important role in the development of modern agriculture.There has been increasing attention to the issue of slow-release fertilizer due to its excellent yield,environmental-friendly properties and saving labor and time.With the industrial lignin as the main material to develop slow-release fertilizer compared to other materials have greater advantages: lignin is a natural polymer organic matter,the preparation of slow-release fertilizer does not cause environment pollution;lignin can delay the nutrients dissolution in the fertilizer to improve the slow-release performance;lignin can inhibit urease activity,reducing the release of NO3-N and increasing the utilization of NH4 +-N;the use of industrial lignin can solve the problem of waste of lignin resources,improve the efficient use of energy and avoid causing the environment pollution.Therefore,lignin had been used to prepare slow-release nitrogen fertilizer in this paper.As an effective modification method,hydroxymethylation can enhance the reactivity of lignin by improving hydroxymethyl content.The structures of the hydroxymethylated lignin and the raw lignin were characterized by FTIR,DEPT 135,HSQC.The structural changes of lignin during the hydroxymethylation reaction were analyzed,and the reaction process was explored and verified.Then on this basis,the hydroxymethylated lignin was used to construct the slowrelease model: the first model was constructed by self-condensation of hydroxymethylated lignin and the second model was set up by hydroxymethylated lignin,calcium alginate gel and sodium-montmorillonite.In this paper,the release characteristics of these slow-release fertilizers were determined by soil leaching and water dissolution rate method under laboratory conditions.The main conclusions are as follows:(1)The results show that the C7,C8 in p-hydroxycinnamic acid units(PCA),ferulic acid ester units(FA),the C-3,C-5 in p-hydroxyphenyl units and C-5 in guaacopine units(G)react with formaldehyde to form hydroxymethyl groups.This hydroxymethylation reaction mainly includes Prings reaction and Lederer-Manasse reaction.While the other units,such as pilocarpine units(S),?-O-4 ether bond structure(A)and phenyl mashed potatoes full(C),do not react with formaldehyde under alkaline condition.The methylation reaction was further optimized by orthogonal test.(2)The optimal conditions of hydroxymethylation are that the reaction temperature is 80?,the reaction time is 3 hours,the pH is 11 and the mass rate of alkali lignin/formaldehyde is 6/1.The hydroxymethyl content is 2.32% under the optimal conditions of hydroxymethylation.(3)The slow-release fertilizer based on three-dimensional networks material was prepared by the condensation of hydroxymethylated lignin to coat the free urea,hydroxymethylurea and urea-formaldehyde polymers.The results of slow-release experiment demonstrated that the product had good slow release property.The nitrogen released did not exceed 75% after being incubated in soil for 25 days.(4)The second slow-release fertilizer based on the release model was prepared by hydroxymethylated lignin,sodium-montmorillonite and calcium alginate gel.The fertilizer has a good slow-release performance.Calcium alginate gel was used as the main carrier.Its concentration directly determined the amount of "package" urea.2% sodium alginate as compared to 3%,4% sodium alginate as a substrate for coating urea had a better slow release performance.Hydroxymethylated lignin also played an important role in the gel matrix of calcium alginate,which improves the slow release activity of "wrapped" free urea and improves the slow release performance of fertilizer.When the hydroxymethylated lignin accounts for 150% of the calcium alginate gel,the slow release rate is best.The cumulative release rate is 19.13%,and the potential release rate is 5.83%.The sodium-montmorillonite with lamellar structure can better regulate the relationship between hydroxymethylated lignin and calcium alginate gel matrix.Lamellar structure constitutes more microporous to wrap urea more effectively.When the amount of sodium montmorillonite is one-third of the content of hydroxymethylated lignin,the three-dimensional network structure constructed by sodium montmorillonite,hydroxymethylated lignin and calcium alginate gel "package" urea more effectively,the slow release performance of fertilizer is also best.