Effect Of Oxidized/Sulphonated Humic Acids On The Availability Of Secondary And Micro-nutrient Elements

Secondary/micro-nutrient elements play an important role in crop growth and development,while the deficiency of them in soils of China has been becoming more and more serious.It is of great significance to develop natural organic substances as enhancers to improve uptake and use efficiency of sencondary/micro-nutrients in soil.As a natural organic compound,humic acid has been widely used in agricultural production to increase the efficiency of NPK nutrients.Studies have shown that the structure of humic acid is an important factor affecting its function on nutirent elements.However,there is a lack of research on the effects of different structural humic acids on the availability of secondary and micro-nutriment elements.In this study,the humic acids with different structures were obtained by modified methods of oxidation?Hydrogen peroxide-H₂O₂?and sulfonation?Sodium sulfite-Na₂SO₃?.The effects of different structural humic acids on the availability of sencondary/micro-nutrient elements in soil-crop system were studied by using incubation experiments and biological experiments.The aim of the study is to provide theoretical basis for the development of functional humic acid materials of sencondary and micro-nutrient elements.The main results are as follows:?1?Both oxidation and sulfonation can reduce the aromaticity of humic acids and increase the content of alkyl carbon and alkoxy carbon,and the effects of sulfonation is more obvious.Oxidation can also increase the number of carboxyl,phenolic hydroxyl,ketone/aldehyde groups,while sulfonation can introduce sulfonic acid group.?2?The content of exchangeable calcium and magnesium was increased by 0.1%¹3.7%and0.9%⁶.6%,respectively after the application of humic acids within the rates of 30³00 mg/kg in incubated fluvo-aquic soil.The available copper content was increased by 32.0%.The application of humic acids increase the available manganese content within 30 days,but the effect on the availability of iron and zinc is irregular.Unactivated humic acid and oxidized humic acid with more carboxyl,phenolic hydroxyl,ketone/aldehyde groups have greater effects on elemental availability than sulfonated humic acid.?3?In red soil,the application of three humic acids of 30³00 mg/kg significantly increased the content available manganese,exchangeable calcium,and exchangeable magnesium respectively by1.3%²4.6%,1.6%⁷.2%and 1.3%⁶.7%in the soil.The effect of sulfonated humic acid rich in sulfonic acid groups on the availability of secondary/micro-nutrient elements in red soil is greater than that of unactivated humic acid and oxidized humic acid.?4?After application of three kinds of humic acids under application dosage of 30³00 mg/kg,the maximum increase of calcium and magnesium uptake was 52.4%and 60.5%.,the uptake of copper,manganese,iron,and zinc in Chinese cabbage plants was increased by 13.7%²1.7%,47.1%⁸3.9%,7.6%⁹.9%and 12.7%²0.8%,respectively.The effect of sulfonated humic acid on the paremiters of Chinese cabbage is greater than that of unactivated humic acid and oxidized humic acid.?5?The application of three kinds of humic acids under the dosage of 30³00 mg/kg can affect the growth and quality of Chinese cabbage in red soil.After application of humic acid,the yield,SPAD value of leaves and soluble sugar content were increased by 3.3%²7.8%,21.1%³5.8%,and 64.6%¹18.5%,respectively.Sulfonated humic acid has a better effect on the quality of Chinese cabbage.