Tobacco-planted Soil Magnesium Nutrient And Effect Of Magnesium Fertilization In Chongqing

China is one of countries having the highest tobacco yield,with more than 400 years tobacco planting history.Since the building up of China,the tobacco industry has been developing rapidly, with planting acreage about 8.0 million mu in 1949 and over 11.0 million mu in the middle of 1970s, particularly in cured tobacco industry.The planting acreage of cured tobacco was about 9.19 million mu and the gross yield has reached 1.0 billon kilograms in the middle of 1970s,both of which took the first place all over the world.During recent years,the supplement of cured tobacco all ovcr the world is more than the requirement,but the yield of tobacco in China has been increasing sostenuto. Chongqing is the main tobacco field in China,with the planting acreages about 47000 hm².The tobacco industry is the leading industry of wu-ling mountain area and three gorges reservoir area, and is also the main source of fiscal levy in some national poor counties such as Pengshui.Shizhu, etc.In recent years,many researches about the N,P,K forms,the reasonable applied quantity and its mixed quota have been done and the planting skills have been normalized.But the research about the middle elements application is very few,especially the research about the magnesium.This paper studies the basic soil nutrient and the content of exchangeable magnesium in the main tobacco field of Chongqing by adopting the methods of investigation and study,soil pot experiment,field investigation and laboratory analysis,with the effect of making clear the content of exchangeable magnesium in the main tobacco field of Chongqing.According to the investigation results,the effects of magnesium fertilizer application dosage on the cured tobacco growth,nutrient absorption, accumulation and the economical character and quality were studied by field experiments,plot experiments and laboratory analysis which were done in test farm of Southwest University,Pengshui and Shizhu counties respectively in 2006.The purposes of this study are to understand the status of exchangeable magnesium content in tobacco-planting soil and to provide the scientific criterion of magnesium fertilizer application for the cured tobacco planting in Chongqing.The main results are as follows:1.The exchangeable magnesium content in tobacco-planted soil of ChongqingYellow soil,pale brown soil,lime soil,purple soil and rice soil are the main soil types in tobacco-planting soil of Chongqing.The content of exchangeable magnesium is lower among these soil types,about 1.11 cmol·kg^-1(n=334)on average,with the change range of 0.15～4.50 cmol·kg^-1. There are about 17.37%of soil sample numbers with the exchangeable magnesium content lower than 0.5 cmol·kg^-1,which are very unfit for tobacco planting,about 47.60%with the exchangeable magnesium content between 0.5 cmol·kg^-1to 1.0 cmol·kg^-1and only about 35.03%with the exchangeable magnesium content higher than 1.0 cmol·kg^-1and are fit for tobacco planting.In the tobacco planting regions in Chongqing,the average exchangeable magnesium content in soil of Nanchuan,Wushan and Wulong counties is lower,which is 0.74 cmol·kg^-1,0.74 cmol·kg^-1and 0.88 cmol·kg^-1respectively.The average content of exchangeable magnesium in Wanzhou,Kaixian, Youyang,Chengkou and Qijiang is higher,and the average content is 1.82 cmol·kg^-1,1.65 cmol·kg^-1,1.64 cmol·kg^-1,1.53 cmol·kg^-1and 1.45 cmol·kg^-1,respectively.In other counties,the exchangeable magnesium content in soil is in the range of 0.92～1.22 cmol·kg^-1.According to the soil types,the exchangeable magnesium content at means is in the decreasing order,i.e.pale brown soil 1.51 cmol·kg^-1＞yellow soil 1.20 cmol·kg^-1＞purple soil 0.83 cmol·kg^-1＞rice soil 0.41 cmol·kg^-1＞lime soil 0.30 cmol·kg^-1.The percentage of magnesium deficiency soil sample number of each soil type is about 27.78%.54.51%.72.22%.100%and 100%respectively.So the magnesium deficiency is much severe in those main soil types of tobacco planting regions in Chongqing.2.The effects of magnesium application on the flue-cure tobacco growth and nutrient absorptionThe plant height,maximal leaf area and the absorption of N,P₂O₅ and K₂O of cured tobacco have a trend of increasing first and reducing afterwards along with the increasing of Mg applied amount under different Mg applied amount.Both the maximum of cured tobacco height and that of cured tobacco leaf area appear in M3 treatment(MgSO₄ 1.76g-pot^-1),the maximum of dry weight of root appears in M2 treatment(MgSO₄ 0.88 g·pot^-1),and both the maximum of dry weight of stem and that of leaf appear in M3 treatment(MgSO₄ 1.76 g·pot^-1).The effect degree is different on the content of N,P₂O₅ and K₂O of different cured tobacco organs under different Mg applied amount but there is no clear regularity.On the whole,the N,P₂O₅ and K₂O content in each organ of cured tobacco of M2,M3 and M4 treatments(MgSO₄ 0.88～3.52 g·pot^-1)is higher than the other treatments.The effect of Mg applied amount on the N,P₂O₅ and K₂O absorption quantity in each organ of cured tobacco is more obvious than that on the N,P₂O₅ and K₂O content in each organ of cured tobacco,which shows that magnesium affects cured tobacco growth firstly and nutrient absorption afterwards.Under different applied amount of Mg,the absorption quantity of K₂O of cured tobacco organs is the largest,followed by N,and the absorption quantity of P₂O₅ is the smallest.The growth and development,dry weight accumulation and nutrient absorption of cured tobacco will be inhabited if the content of Mg is lower than 0.29 g·pot^-1or higher than 5.28 g·pot^-1.3.The effects of Mg fertilization application on flue-cure tobacco in ChongqingThe economical characters and quality of cured tobacco are influenced remarkably by different Mg fertilizer modes and amount of magnesium application.The results show that the effect of leaf spraying mode,which makes the plant directly absorb the nutrient and reduce its fixation and draining in soil,is better than that of basal application.The growth of trunk and leaf of cured tobacco also differs according to different times and consistencies of Mg leaf spraying application.And the effect of Mg leaf spraying in strongly growing stage is superior to rosette stage.The leaf spraying of Mg fertilizer in different growth periods can effectively control the rate of pest incidence.The results show that the spraying at the rosette stage can decrease the incidence rate of Tobacco Mosaic disease more effectively in contrast with the spraying at strongly growing stage,and the same as controlling the incidence rate of Tobacco Brown Spot.Contrasting these two diseases,the effect of Mg fertilizer on controlling Tobacco Mosaic disease is more obvious.The application of Mg fertilizer can hasten the growth and development of cured tobacco and the accumulation of dry substances.It can also improve the botany characters,especially in plant height,available leaf number and maximal leaf area.In the range from 0 to 122.45kg·hm^-2of Mg fertilizer application amount,Mg can increase the yield and the ratio of middle and upper tobacco,average the price and increase the output value.The yield and production output of the M4(MgSO₄ 244.90kg·hm^-2)treatment are the highest,which differs obviously from CK,M1,M2,M3 and M5 treatments.The average price,ratio of middle and upper quality tobacco of M4 treatment(MgSO₄ 244.90kg·hm^-2)are also the highest,which differs significantly from CK.So the content of chemical composition in M4 treatment is the closest to the content of upper quality tobacco and the compatibility of chemical composition is also the best.In conclusion,leaf spraying application of 0.20%MgSO₄ at strongly growing stage or basal application of 61.22～244.90 kg·hm^-2Mg fertilizer can best hasten tobacco growth in tobacco-planting field of Chongqing.