Status Of Soil Nutrients At Different Altitudes And Distribution Of Selenium Contents In Soil And Tobacco Leaves In Southwest Hubei Tobacco-Growing Areas

Serial field survey and laboratory analyses were conducted by this investigation to test the nutrients content in 431 soil samples in 8 countries in southwest of Hubei tobacco-growing areas. The grading of soil nutrients was plotted in southwest Hubei tobacco-growing areas; the comprehensive evaluation of soil fertility at different altitudes of Xuanen tobacco-growing areas was conducted for all the samples. In Xuanen and Xianfeng tobacco-growing areas, contents of selenium in soils of different altitudes and different layers were analyzed, and they were also analyzed in growing leaves of different periods and different cultivars and grades of flue-cured tobacco leaves. The main results were as follows:1. Based on 431 soil samples in 8 countries from southwest of Hubei tobacco-growing areas, the soil nutrients contents and fertility status were analyzed systemically. The results indicated that the content of soil organic matter was rich, with the mean of 32.04 g·kg^-1; the content of soil pH 6.17 was suitable in southwest Hubei tobacco-growing areas; the content of soil total N was rich, with the mean of 2.37 g·kg^-1, the contents of soil hydrolysis N, total P, available P, total K and exchangeable Ca were suitable, with the mean of 157.05 mg·kg^-1, 1.10 g·kg^-1, 14.37 mg·kg^-1, 17.79 g·kg^-1 and 10.25 cmol·kg^-1; the contents of soil available K and exchangeable Mg were low, with the mean of 148.59 mg·kg^-1and 0.37 cmol·kg^-1; the contents of soil available B and available Zn were medium low, with the mean of 0.34 mg·kg^-1and 1.03 mg·kg^-1; the contents of soil available Fe, available Cu and available Mn were richer, with the mean of 21.53 mg·kg^-1, 1.19mg·kg^-1 and 26.99 mg·kg^-1; the contents of soil available S and available Mo were very high, with the mean of 65.11 mg·kg^-1 and 0.14 mg·kg^-1; the content of soil water-soluble Cl was very low, with the mean of only 3.19 mg·kg^-1.2. Take Xuanen tobacco-growing areas for an example, status of soil fertility of 231 soil samples at different altitudes were analyzed and evaluated, and the results showed that: (1) The condition of soil fertility was suitable for high quality tobacco-growing in general, the contents of organic matter, total N, hydrolysis N and available K were rich at higher altitude areas, the content of P was deficient. (2) The contents of organic matter, total N, hydrolysis N, available P, available K and total P reached to significant level between higher altitude and medium altitude, lower altitude. (3)The integrated fertility index of soil fertility at different altitudes was: higher altitude > medium altitude > lower altitude, which reached to significant level between higher altitude and medium altitude.3. The contents of Se in 90 soil samples,58 flue-cured tobacco leaves samples and 204 deenzymed tobacco samples collected during the vigorous growing period were analyzed in Xuanen and Xianfeng tobacco-growing areas. The results indicated that: (1) The soil of this region belonged to Se-rich soil, and 16.7 percent of the soil samples were excessive soil, the highest content of Se upped to 70.84 mg·kg^-1; but there were larger differences in different locations, the coefficient of variation upped to 198.7 percent. (2) In this region, the content of Se in surface soil layers was higher clearly than other layers, and they were higher at middle altitudes (960m and 1004m) than other two altitudes in Xuanen and Xianfeng region; the content of Se at low altitude was lower clearly than middle and high altitudes in all soil layers. (3) The amount of Se accumulation in tobacco leaves increased clearly with the tobacco growth stages extending, highest Se was detected in upper leaves, while lowest showed in lower ones. The Se accumulation of mature stage tobacco leaves appeared as a bimodal curve with the elevation higher, and there were two peaks at the altitudes of 715m and 1004¹228m. (4) The content of Se in flue-cured tobacco leaves was generally in higher levels, but they had quite large coefficient o f variation. Se in tobacco leaves was changed in the sequence: upper leaves > lower leaves > middle leaves, and Se in upper leaves upped to 11.03 mg·kg^-1. Significant differences in the 0.05 level were found for the content of Se between middle leaves and other sites leaves. The Se content in flue-cured tobacco leaves had positive correlation with the elevation higher, but the correlation was not obvious. (5) Analysis of Se contents in flue-cured tobacco leaves among different cultivars showed that the order was: Yuanyan 87 > Yuanyan 85 > K326, but the difference was not obvious. As to the variability of Se content, Yuanyan 85 had a good stability, and K326 was poor.