Magnesium Nutrition Diagnosis Of Flue-cured Tobacco And The Abundance And Deficiency Index Of Soil Magnesium

Magnisium (Mg) is the fourth mineral elements of plants, following N, P, K plays an important role in growth, metabolism and quality of flue-cured tobacco. In recent years, magnesium deficiency is more and more serious in EnShi district, a major tobacco production area in Hubei Province, and become one of the key limiting factors of flue-cured tobacco’s quality. In this study, Nicotiana tabacum Yunyan87was used in a series of soil pot and field experiments during2011to2012to study the abundance and deficiency index of soil Mg and Mg nutrition diagnosis of flue-cured tobacco (FCT). This research was designed to work out the abundance and dieficiency threshold of soil available Mg and diagnosis index of plant Mg nutrition, and to provide the scientific guidance for production of good quality of flue-cured tobacco. The main results were as follows:1. Within a certain range of soil available Mg content, the Mg content in flue-cured tobacco increased with the increasing of soil available Mg content; however, the Mg content in flue-cured tobacco remained stable when soil Mg content exceeded a certain value,. The critical values of soil available Mg content were70-100mg/kg while the Mg content in lower leaves of the plant was between3.2-5.3g/kg.Application of Mg fertilizer significantly increased the Mg content in flue-cured tobacco by6.7%-29.4%, as compared with the no Mg fertilizer control.2. The value of K/Mg ratio in different parts of the flue-cured tobacco was significantly decreased with the increasing of soil available Mg content. The critical value of K/Mg was82-93mg/kg, and the related diagnosis values of K/Mg in lower leaves were7.9-14.2. Application of Mg fertilizer decreased the K/Mg ratio in different growth stages of flue-cured tobacco by approximately7.8%-23.0%.3. With the increase of soil available Mg content, the Ca/Mg ratio in each growth stage of flue-cured tobacco first increased, and then decreased significantly. The threshold range of Ca/Mg value was5.2-11.2, and the soil available Mg contents corresponding to the maximum Ca/Mg ratio were93-102mg/kg. Application of Mg fertilizer significantly increased the Ca/Mg ratio by78.9%-133.0%.4. The content of N, P and K in tobacco plant responsed the soil available Mg content in way of a quadratic curve, increasing firstly and then decreasing. The turning point of N, P and K content were about70-100mg/kg, which was the same with above. N content of23.4-34.6g/kg and K content of60.3-72.3g/kg could indicate the suitable range of soil available Mg content. However, Mg fertilizer application decreased the N, P and K content by0.7%-6.7%,4.7%and2.1%-25.7%-10.5%respectively.5. Soil available Mg content had a significant impact on growth physiology of flue-cured tobacco. With the improvement of soil available Mg content, the antioxidase indexes increased first and then decreased. The maximum enzyme activity of SOD, POD, CAT were at soil available Mg contents of82-93mg/kg, and the related content of MDA, AsA, GSH in lower leaves of the plant were12.3-13.6,1.8-2.5, and2.1-2.5nmol/g respectively. In the mean time, application of Mg fertilizer improved plant height by5.9%-8.0%, activity of POD by0.0-16.6%, and activity of CAT by48.8%-55.5%, but decreased content of MDA by25%in rosette stage, content of AsA by0.0-25.1%in topping stage as compared with no Mg treatment.