1. During the whole growing period, nitrogen fertilizer is the mainstay, and the fertilization principle of “early application of fertilizers to promote growth, control of fertilizers in crops, and resumption of fertilizer production after harvesting” is applied. Many ripe vegetable fields where vegetables are planted year-round have some phenomena of soil aging. The main performance is increased pathogenic bacteria and residual toxicity, soil compaction, lack of organic matter, due to the large number of application of fertilizer, diammonium and other fertilizers, neglect of organic fertilizer application, resulting in soil compaction, reduced permeability, aerobic microbial activity decline, root development, easy Diseased.

2. Excessive application of chemical fertilizers increased the pH of vegetable fields and increased soil salinization. Trace element water-soluble fertilizers are insufficiently applied. For many years, trace elements such as zinc, boron, iron, molybdenum etc. in the soil are absorbed by the vegetables. When they are not supplemented, these trace elements will be reduced year by year, which will seriously affect the growth and development of the vegetables. The soil is ploughed in shallow layers, and the vegetable field is mostly digged by hand. The intercropping and interplanting of the cultivars is less. The soil layer is gradually shallow and affects the extension of the roots. The lettuce growing time is not long because it does not grow vegetables. The above phenomenon, therefore, has a high rate of fertilization and a significant increase in yield.

Lettuce fertilization principles:

To make normal growth of lettuce and obtain good benefits of increasing yields and incomes, it is necessary to apply fertilizers in a reasonable manner so that vegetable fields can maintain appropriate nutrient concentrations and allow lettuce to maintain a moderate plant "seepage" effect. The principles of scientific fertilization are:

1. Add a large amount of decomposed organic fertilizer. In particular, the use of chemical fertilizers and single nitrogen fertilizers should be stopped for cooked vegetables.

2. Adhere to applying organic fertilizers such as plant stalks, manures, and human and animal manure all year round to improve the structure of soil granules so that the water, fertilizer, and air heat are clearly coordinated. For soils that have been acidified or alkalized, in addition to the application of organic fertilizers, appropriate amounts of neutral fertilizers should be applied. For example, the soil can be acidified and can be neutralized with lime and ash, the soil can be alkaline, and ammonium sulfate or superphosphate can be used. Calcium regulation to improve the acidity of vegetable soil.

3. The implementation of reasonable crop rotation in different families, whether it is lettuce or cooked vegetables, should not be in the same vegetable field for several crops of the same species. Should always be turned down.

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