Effects Of Soil Conditions On The Growth, Nutrients Accumulation And Quality Of Flue-cured Tobacco

Soil condition is the main environmental factor that affects the quality of tobacco leaves. Total 13 pieces of fields non-repeated experiments were conducted to study the effect of different soil organic matter (O.M) (<20 g·kg^-1, 20²5 g·kg^-1 and >25g·kg^-1) and texture (Sandy loam, Loam and Silt loam) on growth , dry matter, nutrients accumulation and quality of flue-cured tobacco in Dafang and Bijie, Guizhou province. Also, the relationship between soil suitability indexes and quality of tobacco leaf were analyzed to assess the tobacco-growing soil suitability in Guizhou. The main results obtained were as the following:Different soil O.M and texture had obviously effect on the growth of tobacco. The accumulation intensity of dry matter in the soil with O.M. < 20 g·kg^-1 was the highest at 11 weeks after transplantation while 11 weeks later accumulation in the soil with O.M. > 25 g·kg^-1 became the highest. In the soil with O.M. <20 g·kg^-1, tobacco growth was slower initially, and accumulation of dry matter was higher in the longer later growth period. Tobacco dry matter in sandy loam mainly accumulated before topping, while the accumulation in silt loam last for a longer period. The dry matter accumulation characteristics of tobacco were classified in two types: "S" curve for sandy loam and common loam, and sustaining increase trend for silt loam.The nitrogen accumulation characteristics of flue-cured tobacco were divided into three different types: fast-fast-slow in the sandy loam, slow-fast-stationary in the loam and sustaining increase trend in the silt loam. The peak value of nitrogen absorption appeared mainly between 7 and 9 weeks. In sandy loam and loam with O.M. <20 g·kg^-1, the nitrogen accumulation was the highest. In the silt loam in Dafang, tobacco nitrogen accumulation was the highest in soil with O.M. >25 g·kg^-1, followed by O.M. < 20 g·kg^-1, and in soil with O.M. between 20 and 25 g·kg^-1 was the lowest. The effect on nitrogen accumulation of the three different types of soil texture exhibited as: silt loam exceeded sandy loam and sandy loam exceeded loam. The light soil promoted initial nitrogen absorption and decreased nitrogen absorption in later reproductive period, and therefore reduced the proportion of nitrogen in the tobacco leaf. The absorption and accumulation of phosphorus was similar to American flue-cured tobacco and no obvious variation was observed during the whole growth period.The peak value of potassium absorption appeared between 5 and 7 weeks .There was potassium net loss in tobacco later growth period. The potassium accumulation characteristic curves of tobacco were classified as descending, stationary and increasing trend curve according to the increase decrease or loss of potassium at later periods. As a whole, potassium in tobacco leaves was high when tobacco grew in the sandy loam with soil O.M. < 20 g·kg^-1, loam with soil O.M. ranging from 20 to 25 g·kg^-1 and silt loam with soil O.M. > 25 g·kg^-1.Soil O.M. had a significant effect on dry matter, nitrogen accumulation and final tobacco yield. Soil texture had very significant effect on dry matter, significant effect on nitrogen accumulation but not significant on tobacco yield. The effects of different ecological areas on dry matter, nitrogenaccumulation and yield were very significant. There was no significant effect of Soil O.M., texture and different ecological areas on phosphorus and potassium accumulation.Soil factors and ecological environment were two important factors on quality of tobacco leaves. O.M had significant effect on chemical components, such as nicotine, sugar/ nicotine ratio, nitrogen/ nicotine ratio of lower leaves, and very significant effect on potassium content.Soil O.M. had significant effect on nicotine in the middle leaves and nicotine and sugar/ nicotine ratio in the upper leaves, but it had no significant effect on the other chemical components. Soil texture had significant effect on nicotine in the lower leaves, potassium in the middle leaves and total nitrogen and nicotine in the upper leaves, but it had no significant effect on the other chemical components. Different ecological regions had significant effect on the major chemical components of tobacco leaves. Soil texture and ecological region had significant effect on smoking scores of lower leaves. Soil O.M content and ecological region had significant effect on smoking scores of middle leaves and very significant effect on smoking scores of higher leaves.The correlation between soil suitability index integrated score and chemical components /smoking score of tobacco leaf was very significantly linear with R2 was 0.9514 and 0.9052 respectively. The methods of classification and evaluation of soil suitability index were reliable to assess the soil suitability quantitatively. The assessment results showed that, Eighty percent of Tobacco-growing soil in Guizhou province is suitable or optimal for tobacco plantation. Additionally, 32.5% of the soil can produce high quality tobacco leaf. The most suitable regions mainly centralized in Tongren, Zunyi, Guiyang and Bijie areas.