Studies on soil Mg content and effects of Mg application in tobacco planting areas of Chongqing

The objectives of this study were to investigate the contents of soil exchangeable magnesium and the effects of magnesium application on tobacco production in tobacco planting areas of Chongqing by using the methods of field sampling and field experiments. The results show that the average content of soil exchangeable magnesium is about 1.11 cmol/kg (n=334), and the range is from 0.15 to 4.50 cmol/kg in Chongqing tobacco planting areas. The average contents of soil exchangeable magnesium of the five main soil types are pale brown soil, 1.51cmol/kg; yellow soil, 1.20 cmol/kg; purple soil, 0.83 cmol/kg; paddy soil, 0.41 cmol/kg; and lime soil, 0.30 cmol/kg. The percentages of magnesium deficiency soil samples for the five soil types are about 27.78%, 54.51%, 72.22%, 100% and 100%, respectively. Which indicates the phenomenon of magnesium deficiency is common in tobacco planting areas of Chongqing. The application of magnesium fertilizer can increase the yield, the ratio of mid-grade and high-grade tobacco leaves and the output value significantly. The yield, output value, average price and the ratio of mid-grade and high-grade tobacco leaves of the T4 treatment (MgSO4·7H2O 244.90 kg/ha) are the highest, and there are significant differences between the T4 treatment and the CK, T1, T2, T3 and T5 treatments. Among the magnesium application treatments, contents of total nitrogen, protein and nicotine of leaves are lower than those of the CK treatment, while contents of total sugar and reductive sugar are higher than those of the CK treatment. There are negative correlation between content of K2O of leaves and the rates of the magnesium fertilization. In addition, the chemical composition of the T4 treatment is the best.