First, the invasion of pathogens and pathogens. Through the invasion of pathogens, viruses, and mycoplasma and other pathogens, the root tissue and leaf tissue of fruit trees can be destroyed, such as root rot, root and stem blight, etc., which are the most common and serious, because the various secretions produced by them can be blocked. Conveyance system, so that it can not absorb water and nutrients, the raw materials necessary for photosynthesis can not be supplied, the leaves not only appear chlorotic yellow leaves; sometimes pathogens directly invade the leaves, destroy chlorophyll, directly reduce the ability of the leaves to photosynthesis, make the leaves quickly Yellow leaf disease.
Second, changes in natural conditions. Changes in natural conditions, such as changes in temperature, moisture, and air, can seriously affect the growth and development of fruit trees. When the temperature is too low, the soil nutrients are not easily activated or released, and the crop is difficult to absorb; the temperature is too high, the transpiration of the foliage and the evaporation intensity of the ground increase, resulting in excessive water loss in the soil, and the crop cannot obtain sufficient water supply; Low, in very drought conditions, soil nutrients can not move with the water, spread to the root surface for crops to absorb and use; too much water, such as too much rainfall or excessive irrigation, the air significantly reduced the formation of anoxic conditions, affecting the root system Breathing; under the conditions of viscous texture and soil compaction, poor ventilation, plus high temperature, can not only promote the development and harm of pathogens, but also affect the gas exchange and absorption of the root surface, the root vitality significantly weakened. These changes in natural conditions can all obstruct the absorption and utilization of nutrients, moisture, and gases in the roots, resulting in chlorosis and yellowing of the leaves.
Third, the lack of soil. The lack of soil is the most direct and sensitive factor in the yellow leaves of fruit trees. There are many kinds of nutrients in the yellow leaves of fruit trees, such as nitrogen, potassium, magnesium, manganese, zinc, sulfur, boron, iron and other elements, can make leaves produce yellow leaves. Only the degree and characteristics of "yellow leaves" are different. With the improvement of the level of scientific farming, many of them are able to use special fertilizers with different functions to correct and overcome the adverse effects caused by lack of supply. However, the lack of iron is far from being solved by general fertilization. Because the iron is so denatured that it is difficult to keep the iron in an effective state, the problem of iron deficiency correction should be treated with emphasis.
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