Fertilization of flue-cured tobacco must comply with the needs of the cigarette formula, and should not blindly pursue high yield, but should aim at high quality and suitable yield. Only in this way can the sustainable development of "two cigarettes" be ensured.

(1) Principles of flue-cured tobacco fertilization

Correct flue-cured tobacco fertilization should be based on the type of flue-cured tobacco, characteristics of the variety, soil fertility conditions, fertilizer properties, temperature during the growth period of flue-cured tobacco, rainfall, etc. The situation is used as a basis to obtain the appropriate yield of tobacco leaves to determine the appropriate nitrogen dosage, nitrogen, phosphorus and potassium ratio, fertilizer type, base fertilizer dosage and application method.

① Principle of nutrient balance

The normal growth and development of flue-cured tobacco and the formation of yield and quality require a variety of nutrients necessary for the tobacco plant. Moreover, there is a balanced proportional relationship between these elements. For example, as the amount of fertilizer increases, the middle and upper leaves of tobacco plants often become green and white during the maturity process, which is caused by the imbalance of magnesium in tobacco plants. Nutrient balance is the basic principle of balanced fertilization. If you ignore this principle and blindly increase the dosage of a certain nutrient element, the yield and quality of tobacco leaves will be affected.

②Principle of soil-based fertilization

The main soils for growing tobacco in Double Cypress include yellow soil, paddy soil and purple soil. It can be divided into two categories according to its water conditions. One is mountainous soil such as purple soil, which has low groundwater level, less fertilizer loss and high fertilizer utilization rate; the other is paddy soil and yellow soil with high groundwater level, which has fertilizer loss. Large and low utilization rate. Therefore, the application rate of field tobacco is generally higher than that of field tobacco.

③ Principle of fertilization according to varieties

Different flue-cured tobacco varieties have great differences in the absorption and utilization of soil and fertilizer nutrients due to their genetic characteristics. Honghua Dajinyuan (referred to as Hongda) has higher nitrogen, phosphorus and potassium fertilizer utilization rates, while K326 has lower fertilizer utilization rates. Therefore, under certain conditions, the difference in fertilizer requirements of tobacco varieties is the main basis for determining the amount of fertilizer. Different varieties use different nitrogen, phosphorus, and potassium ratios. The suitable fertilizer ratio for varieties with weak fertilizer tolerance such as Hongda and G28 is that the N and P2O5 contents are both 8% to 12%, and the K2O content is 20% to 25%. Suitable, that is, N:P2O5:K2O=1:1:2.5~3. For varieties with strong fertilizer tolerance such as K326 and Yunyan 85, the N content in the fertilizer ratio is 12% to 18%, the P2O5 content is 5% to 8%, and the K2O content is 22% to 28%. That is, N:P2O5: K2O=1:0.5:2～2.5.

④ Principle of climate-based fertilization

Climate conditions mainly refer to the amount of rain and temperature during the tobacco field period. In years with heavy rainfall, fertilizer loss is large, the temperature decreases accordingly, and fertilizer utilization rate decreases. The amount of fertilizer used in tobacco, especially nitrogen fertilizer, needs to be appropriately increased. On the contrary, the amount of fertilizer should be appropriately reduced.

(2) Fertilization methods and periods

Under different climate conditions, tobacco fields with different soil properties must use different fertilization methods due to different release, loss and absorption of nutrients. Method to give full play to the effectiveness of fertilizers and regulate the nutrient supply to tobacco plants.

When fertilizing Doublecypress flue-cured tobacco, most of them use a combination of base fertilizer and top dressing. In order to promote the growth of tobacco plants in the early and middle stages, heavy application of base fertilizer is mostly used, with 2/3 or more of the total fertilizer amount used as base fertilizer, and the rest as top dressing. The role of top dressing is not only to ensure the supply of nitrogen during the middle and later stages of growth and prevent premature defertilization and premature aging during the maturity period, but also to increase or decrease the original amount of top dressing according to the appearance, soil and climate conditions of the tobacco plants in the field to correct the problem. The original planned amount of fertilizer. If all fertilizers are used as base fertilizer, it will be difficult to reverse the adverse effects on quality when the designed fertilizer amount is too much. Therefore, top dressing is also a remedial measure to adjust nitrogen. Moreover, top dressing can be applied to weak and small seedlings to encourage them to catch up with strong seedlings, which is also an effective means to achieve consistent growth in the field. For those tobacco fields with poor water and fertility retention, relatively low potential nitrogen, and weak nitrogen supply capacity in the later period, as well as areas with excessive rain in the early and middle stages and serious soil and nutrient loss, top dressing can ensure the nitrogen supply of tobacco plants in the middle and later stages. An effective means to supply nutrients and stabilize yield and quality.

The 15N tracer test showed that the nitrogen fertilizer utilization rate was lower in the whole-strip application treatment, in the middle in the 2/3 base fertilizer and 1/3 top-dressing treatment, and in the 1/3 base fertilizer and 2/3 top-dressing treatment it was higher. However, when the proportion of top dressing reaches 50%, the nicotine content in the middle and upper leaves increases significantly, which is detrimental to improving the quality and usability of tobacco leaves. Therefore, the proportion of top dressing should be controlled at 30 to 40%.

Mastering the appropriate fertilization method and period can improve tobacco yield and quality and fertilizer utilization rate. In actual production, the following issues should be paid attention to:

① Compound fertilizer and potassium sulfate should be based on Depending on the level of groundwater level and fertility, it is recommended to apply less or no pond fertilizer (if the soil fertility is low, apply less, and if the soil fertility is high, apply no fertilizer), and reposition ring fertilization or top dressing (when the groundwater level is low, reposition ring fertilization. Such as ground smoke and mountain smoke; if the groundwater level is high, top dressing is required, such as field smoke).

② Calcium or calcium magnesium phosphate fertilizer is suitable for strip application, that is, evenly applied to the bottom of the soil before moisture management, which can improve fertilizer efficiency. In addition, calcium magnesium phosphate fertilizer is an alkaline fertilizer and should not be mixed with acidic fertilizers such as compound fertilizers or potassium sulfate to avoid chemical reactions that will reduce fertilizer efficiency, and the application effect is better on acidic soil.

③ It is necessary to prevent direct contact between fertilizer and the roots of tobacco plants. Use the ring fertilization method to keep a distance of 10 to 15cm between the fertilizer and tobacco plants to avoid burning the seedlings.