Effects Of Organic Carbon Pool On Soil Nutrient Availability And Flue-cured Tobacco Yield And Qualit

The type and content of soil colloid determine the soil nutrient adsorption/desorption characteristics.Organic colloid has the greatest influence on soil nutrient adsorption/desorption characteristics.Therefore,it is inevitable to study the influence of soil organic carbon pool on nutrient adsorption/desorption characteristics and divide soil organic carbon content into several levels for fertilization according to the research results.The influence mechanism of soil organic carbon pool on nutrient adsorption/desorption was studied.The effects of soil organic carbon pool on soil nutrient availability and flue-cured tobacco yield and quality were investigated.On this basis,the optimal application ratio of chemical fertilizer and organic fertilizer for flue-cured tobacco under different organic carbon pool contents can be constructed.Through the research,the following results are obtained:（1）Using the aggregate dry sieve method to separate Fifty-four soil samples what Collected from tobacco-growing soils to get AC and IC.The Langmuir equation was obtained by nitrogen,phosphorus and potassium adsorption/desorption tests for all soils.The effects of different organic carbon pools on nutrient adsorption/desorption were discussed here.The results showed that AC and IC showed positive adsorption on NH₄⁺,PO₄^3-and K⁺.The adsorption of AC and IC on NO₃^-is negative at low concentration and positive at high concentration.The adsorption affinity of AC for NH₄⁺,PO₄^3-and K⁺was higher than that of IC.AC has stronger rejection ability to NO₃^-than IC.The desorption rate of AC after adsorption of NH₄⁺and K⁺is lower than that of IC.The desorption rate of AC after adsorption of PO₄^3-is higher than that of IC.AC content was positively correlated with the adsorption sites of NH₄⁺,PO₄^3-and K⁺,and r were 0.491**,0.456**and0.556**,respectively.AC content was positively correlated with the maximum negative adsorption value of NO₃^-,r=0.499**.IC content was positively correlated with the adsorption sites of NH₄⁺,PO₄^3-and K⁺,and r were 0.462**,0.308*and 0.545**,respectively.IC content was positively correlated with the maximum negative adsorption value of NO₃^-,r=0.448**.（2）Randomly selected 6 soil samples to explore the differences in nutrient adsorption/desorption characteristics of organic carbon pools and mineral particles using the Langmuir thermodynamic equation.The results showed that the adsorption capacity of mineral particles for NH₄⁺,PO₄^3-and K⁺was stronger than that of organic carbon.The desorption rate of mineral particles to NH₄⁺,PO₄^3-and K⁺is lower than that of organic carbon.When the concentrations of NH₄⁺,PO₄^3-and K⁺in soil were low（<68.55mg/kg,<457.39mg/kg,<358.13mg/kg,respectively）,the nutrient availability was mainly affected by the adsorption capacity of mineral particles.When the concentrations of NH₄⁺,PO₄^3-and K⁺in soil were high（≥68.55mg/kg,≥457.39mg/kg,≥358.13mg/kg,respectively）,it was mainly affected by the adsorption capacity of organic carbon pool.（3）In the tobacco planting soil of the research area,the concentrations of PO₄^3-and K⁺are below the threshold,and adsorption is mainly determined by mineral particles.The concentration of NH₄⁺in tobacco-planting soil was higher than the threshold value,and there was adsorption of both mineral particles and organic carbon pool.The adsorption amount of NH₄⁺in organic carbon pool is greater than that of mineral particles.Since the organic carbon pool content（x）mainly affects the NH₄⁺availability（y）,the correlation between the two can be fitted by the function y=24.930x-67.318.The appropriate range of available nitrogen in tobacco-growing soil（100-150mg/kg）and the maximum available nitrogen content in soil after flue-cured tobacco fertilization（400mg/kg）were substituted into the function to obtain the corresponding organic carbon pool content.Accordingly,tobacco-growing soil in the study area was divided into LOC（<8.72g/kg）,MOC（8.72-18.74g/kg）and HOC（>18.74g/kg）.（4）In HOC,MOC,and LOC soils,organic fertilizers were respectively applied at 0,200,and400kg/667m² to explore the response relationship between soil organic carbon content and composition and the amount of organic fertilizer applied.The results showed that the application of organic fertilizer in HOC had no significant effect on the content of organic carbon,but it could increase the activity of organic carbon in soil and make organic carbon accumulate to AC.The application of organic fertilizer in MOC can increase TOC and AC,and the improvement effect and the application amount of organic fertilizer show a trend of first increasing and then decreasing.Application of organic fertilizer in LOC significantly increased TOC and AC in soil,and increased with the increase of application amount.（5）Using Box-Behnken to obtain the optimal application ranges of nitrogen and organic fertilizers in HOC,MOC,and LOC.The application range of nitrogen fertilizer of HOC is6.7-7.1kg/667m² and the application range of organic fertilizer is 150-210 kg/667m².The application range of nitrogen fertilizer of MOC is 6.5-7.5 kg/667m² and the application range of organic fertilizer is 140-200 kg/667m².The application range of nitrogen fertilizer of LOC is7.5-8.5 kg/667m² and the application range of organic fertilizer is 300-400 kg/667m².