Effects of Different Preceding Crops on Conditions of Tobacco-planting Soil Nutrients, Enzyme Activities and the Growth of Flue-cured Tobacco

In order to study the effects of different preceding crops on the nutrients of tobacco-planting soil and on growth, yield and quality of flue-cured tobacco, a field experiment was conducted by using winter fallow and garlic and green manure. The results showed that:(1) Compared with the winter fallow treatment, the garlic and green manure treatments significantly decreased soil pH by 0.48 and 0.46 units, while increased soil available potassium by 108.80 and 217.39 mg/kg respectively. Garlic and green manure treatments significantly increased the contents of soil available phosphorus, available potassium and soluble organic carbon, and the effects of green manure were significantly higher than those of garlic. Both garlic and green manure treatments significantly enhanced the activities of soil invertase and urease and the effect of green manure was higher than that of garlic. (2) Compared with the winter fallow treatment, tobacco biomass of the garlic treatment was similar 30 d after transplanting, but significantly higher 60 d after transplanting. Tobacco biomass of the green manure treatment was significantly lower 30 d after transplanting, but became significantly higher than that of the winter fallow treatment 60 d after transplanting. The same trends were found in the effects of different pre-treatments on absorption of nitrogen and potassium in flue-cured tobacco. (3) The garlic and green manure treatments increased the yields and output values of tobacco, but the green manure treatment increased nitrogen content in tobacco leaves, thus significantly decreased the sensory evaluation quality of tobacco leaves. Therefore nitrogen fertilizer should be reduced when planting tobacco in this case. Overall, the preceding crops garlic and green manure could improve the soil conditions of the tobacco field to a certain extent, and increase the yield of tobacco leaves, but the amount of fertilizer should be reduced properly after the green manure was returned to the field.