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Our country has more people and less land, and the continuous cropping phenomenon is widespread. Studies have shown that poor continuous cropping, reduced yield, and unsatisfactory quality of soybeans may be due to difficulties in nutrient uptake by roots, reduced bioavailability of trace elements, malnutrition of soil, and thus affecting the nutritional balance of plants. Long-term continuous cropping of vegetables, wheat, corn, etc., will also lead to soil nutrient imbalance and reduce crop yields.
In actual production, long-term continuous production of flue-cured tobacco also produces a series of production problems such as soil, nutrition, yield and quality. The long-term succession of flue-cured tobacco reduced the biomass and tobacco leaf quality, reduced the potassium content and sugar content of tobacco leaves, increased the content of nicotine, and deteriorated the aroma quality.
Some experts have investigated soil nutrient status of continuous cropping of flue-cured tobacco with soil nitrogen, phosphorus and potassium detectors. It was found that the total soil nutrient content did not change much, effective nutrients increased, and the proportion changed. Long-term continuous cropping suppression of tobacco plant growth and yield quality were due to soil nutrient imbalance. . This shows that long-term continuous cropping of flue-cured tobacco will indeed change soil properties, affect the growth of tobacco plants and the quality of tobacco leaves.
Soil Available Nitrogen (Ammonium Nitrogen, Nitrate Nitrogen): Nitrogen is the most sensitive and most sensitive element of all nutrient elements affecting tobacco leaf quality and yield. Nitrogen absorbed from soil by tobacco plants mainly includes nitrate nitrogen and ammonium nitrogen. The results show that the nitrate content of yellow lime soil suitable for tobacco is significantly higher than that of Quaternary yellow soil. As the number of continuous cropping seasons increased, the nitrate nitrogen content in the soil showed a significant upward trend. For the six seasons, the nitrate nitrogen content in the yellow limestone soil increased from 354 mg/kg to 1,619 mg/kg, which was 4 times higher than the original. More, Quaternary yellow earth also has this trend. The change in ammonium nitrogen is not the same as nitrate nitrogen. In the yellow lime soil, the ammonium nitrogen content in the soil increased significantly with the increase of the continuous cropping season, which was similar to that of nitrate nitrogen. The quaternary yellow soil showed the characteristics of long fall and long afterwards. The six seasons continuous cropping variation was much smaller than the yellow lime soil. .
Taking into account the aforementioned tobacco plant biomass, the increase in soil nitrogen content did not contribute to the increase in biomass of tobacco plants, indicating that long-term continuous cropping, the main factor in controlling the growth of flue-cured tobacco may not be soil nitrogen.
Soil Available Phosphorus: Phosphorus is one of the main elements for the growth of flue-cured tobacco, and it is also critical for the quality of tobacco leaves. In China's tobacco area, the available P content is less than 3~5mg/kg, accounting for more than 50%. The test results show that the available phosphorus content of the test soil is at a high level. Among them, the available phosphorus content in the soil of Quaternary yellow soil was significantly higher than that of yellow lime soil, which was related to the pH value of the soil in Quaternary yellow soil was significantly lower than that of yellow lime soil. With the increase in the number of continuous cropping seasons, the available phosphorus content in both soils increased significantly. Yellow lime soil increased more than 6 times, and the Quaternary yellow soil was more than four times higher.
Potassium in soil: Potassium is an important quality element of tobacco. Because the potassium content in soil is generally low in China, the large amount of potassium fertilizer is an important fertilizer rule for flue-cured tobacco production. The results showed that the effective potassium content in different types of soils did not differ greatly and remained in the third season of flue-cured tobacco continuous cropping. From the fourth quarter, the effective potassium content of yellow lime soil suitable for tobacco increased significantly with the continuous cropping season, and It is much higher than the Quaternary yellow earth, which is not suitable for smoke.
Experiments show that soil organic matter changes in long-term continuous cropping are not significant. The reason may be that after the end of each season of the test soil, the larger tobacco plant residues in the soil are cleared, and other exogenous organic materials are prevented from entering the test soil. Therefore, there is not much inorganic nitrogen formed by organic nitrogen mineralization. It is indicated that the large amount of exogenous inorganic nitrogen is the main reason for the apparent increase of soil nitrogen (nitrate nitrogen, ammonium nitrogen). This may be the main reason why the content of phosphorus and potassium increased significantly with the number of consecutive crops.
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