Effects Of Soil Acidity On Growth And Soil Traits Of Different Flue-Cured Tobacco Varieties

The study showed that the acidification level of tobacco planting soil（pH<5.5）in Chongqing reached 41.0%.Therefore,in order to explore the effects of different pH values on the growth and development of flue-cured tobacco and soil properties,and reveal the differences in yield and quality of flue-cured tobacco under different pH values,this study selected the main flue-cured tobacco varieties Yunyan87,K326,and Yunyan 116 in Chongqing tobacco region,and conducted water culture experiments,pot experiments,and field experiments,respectively.The water culture experiment was conducted with three treatments: pH 4.0,pH 5.0,and pH 6.0;The pot experiment was conducted with three treatments: pH 4.66,pH 6.00,and pH 7.34;Field experiments were conducted on strongly acidic soil（pH 4.62）.Through the above experiments,the effects of different pH values on the growth and development,yield and quality,and soil characteristics of the three main flue-cured tobacco varieties were explored,with a view to providing a theoretical basis for screening acid tolerant flue-cured tobacco varieties and improving acidic soil.The experimental research results are as follows:（1）Under acid stress（pH 4.0 and pH 5.0）,root activity of flue-cured tobacco seedlings decreased,root development was slow or even inhibited,and chloroplasts and mitochondria were damaged to varying degrees;The content of malondialdehyde（MDA）and the activities of superoxide dismutase（SOD）,peroxidase（POD）,and catalase（CAT）in leaves increased.Compared with pH 5.0 treatment,after 6 days of treatment,the root length,root surface area,root volume,and root tip number of fluecured tobacco seedlings treated with pH 4.0 decreased;Chloroplast swells and deforms,grana lamellae layers twist,mitochondria cavitate,and there are no welldefined ridges.MDA content in leaves increases,and the activities of SOD,POD,and CAT decrease.Acid stress inhibits root development of flue-cured tobacco seedlings,damages the subcellular structure and antioxidant enzyme system of leaves,and with the decrease of pH,the damage degree of flue-cured tobacco seedlings is higher.Yunyan 87 showed strong acid resistance,followed by K326,and Yunyan 116 was significantly affected by acid stress.（2）In the pot experiment,the contents of hydrolytic acid,exchangeable acid,exchangeable hydrogen,and exchangeable aluminum in the soil treated with pH 4.66 were significantly higher than those of the treatment with pH 6.00,while the contents of exchangeable calcium and exchangeable magnesium in the soil were significantly reduced.Compared to the pH 7.34 treatment,the soil nitrate nitrogen content of the treatment with pH 4.66 and pH 6.00 decreased,while the soil ammonium nitrogen content increased,and nitrification weakened.After 75 days of transplanting,the number of soil bacteria and actinomycetes in the treatment of pH 4.66 decreased by39.28% and 58.45% respectively compared to the treatment of pH 6.00,while the number of soil fungi increased by 75.47%.With the increase of soil pH,the AWCD value of soil microorganisms decreased in a trend of first increasing and then decreasing,and the utilization ability of soil microorganisms to carbon sources such as sugars,amino acids,carboxylic acids,and polymers also showed the same trend.Compared to the treatment with pH 6.00,the treatment with pH 4.66 decreased the net photosynthetic rate,transpiration rate,and stomatal conductance of flue-cured tobacco leaves,while the intercellular CO₂ concentration increased.When harvested at maturity,compared to the treatment with pH 6.00,the nitrogen accumulation of fluecured tobacco at pH 4.66 in Yunyan 87,K326,and Yunyan 116 decreased by 30.78%,39.73%,and 39.97%,respectively.The accumulation of phosphorus,potassium,calcium,and magnesium in the tobacco plant decreased,while the accumulation of manganese and aluminum in the root tip increased.The growth of tobacco plants treated with pH 4.66 was poor,and the growth and development of flue-cured tobacco were inhibited.When harvested at maturity,the dry matter accumulation of flue-cured tobacco in Yunyan 87,K326,and Yunyan 116 decreased by 30.90%,38.10%,and38.89%,respectively,compared to pH 4.66 and pH 6.00.Compared to the treatment with pH 6.00,the total sugar,reducing sugar,and potassium content of flue-cured tobacco leaves increased and the nicotine content decreased after the treatment with pH 4.66.The two sugar ratio,sugar base ratio,and potassium chloride ratio of K326flue-cured tobacco leaves were within the appropriate range,and the chemical composition of K326 flue-cured tobacco leaves had the best coordination.（3）The results of field experiments showed that on strongly acidic soil,there were no significant differences in the growth and development of the three flue-cured tobacco varieties in the early stage,but significant differences appeared in the middle and late stages.The agronomic traits such as plant height,stem circumference,maximum leaf length,and maximum leaf width of Yunyan 87 were the best,followed by K326,and Yunyan 116 was the worst.The flue-cured tobacco leaves of Yunyan 87 have the highest content of nitrogen,phosphorus,potassium,calcium,magnesium,and trace elements copper,zinc,and boron,with the highest yield,output value,average price,and the highest proportion of medium to top grade tobacco.The incidence rate of four diseases of Yunyan 87（bacterial wilt,climate spot,tobacco mosaic and anthracnose）is relatively low.The content of total sugar,reducing sugar,and nicotine in flue-cured tobacco leaves of variety K326 is within the appropriate range for high-quality tobacco leaves,and its internal chemical components are more harmonious,followed by Yunyan 116,and Yunyan 87,which is slightly worse.The middle leaf of K326 has good hair permeability,mellow,sweet and fragrant aroma,balanced smoke,and the best sensory quality;Yunyan 87 has a weak aroma,heavy impurities,and the worst sensory quality.Comprehensive research results show that lower pH values affect soil characteristics,thereby inhibiting root development,affecting nutrient absorption,growth and development of flue-cured tobacco,and reducing the yield and quality of flue-cured tobacco.Yunyan 87 showed strong acid resistance,followed by K326,and Yunyan 116 had the worst acid resistance,but the quality of cured tobacco leaves from K326 was better than that from Yunyan 87.