| Tobacco is an important economic crop in China. Hunan has been confirmed asfit and optimum flue-cured tobacco tobacco-planted region in Chinese tobaccoplanting regionalization. As one of the main tobacco-planted regions, tobacco plantingarea in Hunan covers 60,000-80,000 hm2, and the tobacco leaves has been Purchasedmore than 1.3×105 t per year. Tobacco industry is not only the leading industry ofbreaking away from poverty but also the primary resource of finance and revenue intobacco-planted regions in Hunan. Currently, being lower quality tobacco, and lesscompetitive in international market is the most important problem of tobaccoproduction all over the country. As a crop which should be paid equal attention toyield and to quality, the quality of tobacco is subjected to soil, breed; plantingtechnique, climate and cool technology, etc. Especially the soil is the dominant factor.Magnesium is the key element to tobacco growth, and its content relates to tobaccoquality intimately. In recent years, the deficiency of Mg in tobacco planted soils hasoften been reported. Because of Mg deficiency, it leads to the inconsistent nutrientand influences the further improvement of tobacco quality and competition.Based on the technique of GIS, the method of field sampling, indoor analysis,field test and water culture experiment, and the application of SPSS soft andmathematic models, this study analyzes and estimated the Mg content of tobaccoplanted soils and Mg accumulation, distribution of tobacco leaves, and studies someregulation and control ways to enhance Mg content in tobacco leaves.The results are as following:1 The average exchangeable Mg in tobacco planted soils in Hunan provincewere 1.317cmol/kg, and there are about 40％on the low side of total areas. Theaverage Mg content in tobacco leaves in Hunan was 0.378％, and Mg deficiency oftobacco leaves were reached to 66.3％of total areas. The correlation coefficientbetween exchangeable Mg in soil and Mg content in tobacco leaves were reached tosignificant level. Both exchangeable Mg in tobacco planted soils and Mg content in tobaccoleaves in tobacco-rice multiple cropping in paddy field were significant higher thanthat of dry land tobacco monoculture. There was only 22.7％exchangeable Mgdeficiency in dry land tobacco monoculture while about 50％exchangeable Mgdeficiency in tobacco-nee multiple cropping in paddy field. In tobacco leaves therewas 40.6％gentleness Mg deficiency in dry land tobacco monoculture and about 75％gentleness Mg deficiency in tobacco-rice multiple cropping in paddy field. Along withthe years of tobacco planting expand exchangeable Mg in soil tended to decline.2 The quantified relationship between Mg content and chemical components intobacco leaves were that Mg content have positive correlation with that of total sugar,total chlorine, total nitrogen while have negative correlation but no significantdifference with total sugar and potassium content reducing,. Mg content have positivecorrelation with that of total alkaloid also and the difference were significant; andpositive correlation with average weight per cigarette, total particle phase content,nicotine quantity in smoke, tar quantity, frequency of smoke, tar quantity/caporal pergram; negative correlation with that of moisture of smoke and the difference weresignificant; positive correlation with aroma quality, aroma quantity, offensive odor,smoke concentration, physiological strength, lingering odor, after-taste, total smokingquality scores while have negative correlation with combustibility and ash-color, butno significant difference.3 The main agronomic characters of height, ceiling Lai, stem girth waspronounced influenced by the concentrations of different Mg except the number ofleaves; when Mg concentration was 2-4mmol/L, the dry matter accumulation offlue-cured tobacco was higher than that of other treatments; Neither Mg deficiencynor Mg excessive benefit to the growth of flue-cured tobacco. Different Mgconcentrations have no significant influence on N content in tobacco leaves. P contentin tobacco leaves with Mg concentration 2-8mmol/L was significant higher than thatof other treatments and K content in tobacco leaves was also significant higher thanthat of other treatments under Mg concentration 1-4mmol/L. The Mg and nicotinecontent of tobacco leaves have a significant positive correlation with Mg concentration while Ca content of tobacco leaves have a significant negativecorrelation with different Mg levels.4 Chlorophyll contents in tobacco leaves were increasing when the Mgconcentration increased from 0 to 2mmol/L, while above 2mmol/L decreased, andboth decreased significantly when Mg-deficiency and Mg- excessive. The Effectivequantum yield (EQY), Electron transport Rate (ETR) and Non-photochemicalquenching (NPQ) were all the highest at the concentration of 8mmol/L Mg. Tobaccoleaves have largest adaptability to excess light intensity at 8mmol/L Mg concentration.Both Mg-excessive and Mg-deficiency leads to the decline of the Effective quantumyield, suffocated the Electron Photosynthetic rate and reduced the dissipation ofexcessive excitation energy.5 The root activity was the highest at knee-high stage and vigorous stage,with the extended of growth period duration of tobacco the root activity tended to belower. The root activity was the best at the concentration of 4mmol/L Mg in everygrowth stage. Nitrate reductase (NR) activity among all treatments were: vigorousstage＞knee-high stage＞mature stage, and the effects of 8mmol/L Mg concentrationtreatment was the best, nitrate reductase (NR) activity put up Consistency with drymatter accumulation nicotine content.Mg stress leaded to an increase of super-oxide dismutase (SOD) activities.Application of Mg decreased SOD activities while Mg concentration above 4mmol/Lthe SOD activities increased. Peroxidase (POD) activity was the highest under Mgstress, and POD activity decreased with Mg concentration increasing. Mg stressleaded to decrease catalase (CAT) activities. CAT activities were increased with Mgapplication while decreased when Mg concentration was above 4mmol/L.Malondialdehyde (MDA) content rose under the stress of Mg, and MDAcontent was the highest at the concentration of 4mmol/L Mg. MDA content among alltreatments were: mature stage＞vigorous stage＞knee-high stage, and the effect of8mmol/L Mg concentration treatment was the best, nitrate reductase (NR) activity putup Consistency with dry matter accumulation nicotine content. Ca,Mg-ATPaseactivity in tobacco leaves among all treatments reached to the highest at vigorous, and every stage 8mmol/L Mg concentration treatments were the highest, so didPhotophosphorylation reaction in tobacco leaves.6 Rational Mg concentrations can increase the thickness of tobacco leaveswhile decreasing under Mg stress. Mg deficiency can increase the thickness ofpalisade tissue in tobacco leaves while decreasing the cell number of palisade tissue,and resulting in a decrease of the palisade tissue area in tobacco leaves.7 Results of field experiments indicated that rational application of Mg canpromote the growth and development of tobacco effectively, and improve yield,balance the chemical components of tobacco leaves and as a result the quality oftobacco leaves were improved. Under the condition of this experiment the optimistMg application was 300kg/hm2 MgSO4·7H2O, and the agronomic characters, all ofdry matter accumulation, yield, tobacco leaves quality were the best.8 Varieties of K326, NC82, G80 have the highest Mg content in leaves in 8varieties that were widely planted in Hunan and Mg content significantly higher thanother varieties. Mg content of Cuibi No 1 was the lowest among all varieties.9 Straw residue and green manure-returned can obviously increase Mg contentof tobacco leaves. In all green manure-returned treatments the Mg content in tobaccoleaves were significantly higher than non-returned treatments, and the tendency wasthe Mg content in tobacco leaves increased with the returned quantity increasing. Indifferent straw-returned ways, straw incorporation increased Mg content in tobaccoleaves was superior to straw mantle. Tobacco-rice-green manure and tobacco-maizepatterns were favor of Mg content in tobacco leaves increasing, while that oftobacco-rice pattern was the lowest.
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