First, the main features of iron deficiency Iron deficiency is more common in northern China, especially in calcareous soil or soil with high pH, ​​especially saline soil. Since iron is an indispensable element in the formation of chlorophyll, iron deficiency will make it difficult for iron to be reused in plants. Therefore, the symptoms of iron deficiency are mainly the chlorosis of the top or young parts. In the early stages of chlorosis, the veins remain green. With the increase of iron deficiency, the leaves change from light green to grayish green. In some cases, brown spots appear on the leaves. In the case of severe iron deficiency, the entire leaf is yellow, white or shed, and even the entire leaf is completely detached. The tender shoots are prone to death and the plant tips wither.
In grasses and other crops, iron deficiency is rarely seen under normal field conditions. Although it sometimes occurs, most of them are caused by the influence of other elements. For example, there is a high amount of phosphorus in the soil. In the early days of iron deficiency in these crops, the new leaves are prone to chlorosis, the veins remain green, and the entire new leaf becomes chlorogenic when severely iron-deficient. Leaf affected by iron deficiency usually wither and dry. The soybeans in dicotyledonous plants are significantly affected by iron deficiency. Since iron is a component of heme heme and nitrogenase, the iron deficiency causes the nitrogen fixation of Rhizobium to decrease and the plant growth is short. In the early stage of iron deficiency, the upper leaves turn yellow and have a slight curl with green veins. This yellowing phenomenon is further developed until the new leaves turn yellowish white. In extreme shortage, many brown spots of necrotic tissue appear near the edges of the leaves.
In southern China's acid-stained paddy fields, ferrous iron appears to be toxic. The symptoms are the appearance of small brown spots between the veins of the lower leaves of rice. The spots spread from the tip to the base, and the leaves are dark green, somewhat like potassium deficiency. When severely poisoned, the leaf color is purple brown or brownish yellow. The roots are black or rot.
Second, the main features of zinc deficiency In recent years, there are many reports on zinc deficiency in crops at home and abroad. Because zinc affects the formation of auxin, the lack of zinc will cause the plant to be short, internodes short clusters, leaf expansion and elongation are blocked, there are leaflets, leaf edges often appear distorted and wrinkled. The pulsation between the veins appears first in the vicinity of the midrib and may develop into brown spots and tissue necrosis. The general symptoms are first manifested in new tissues. For example, the chlorosis of new leaves is grayish green or yellow-white, the growth and development are delayed, the fruits are small, and the root growth is poor.
Zinc deficiency in rice has obvious symptoms in the seedling stage. Severe rice Zn deficiency has been found in calcareous soils and coastal saline soils in China. Symptoms usually appear about two weeks after transplanting. The most obvious symptoms are at the time of delivery. The leaves turn white and the leaves are narrow and narrow. Seedlings are not stiff, so they are called "dwarf seedlings." Severe emergence of dead seedlings, the whole field landscape was brownish or brownish red, looks uneven, and in some places it is also called "red seedlings." When 5-6 leaves per plant, the base of the new leaves first faded green and faded white, the older leaves of the lower part of the plant showed chlorotic stripes along the main veins, and the middle ribs of the rice leaves had brown spots on both sides, which in turn expanded. A round or oval plaque. Brown spots also appear on sheaths and stems when severe. The leaf veins of the lower old leaves are brittle and easy to break or shed, and the spacing between the fourth and fifth leaf sheaths is reduced and the leaf pillows are juxtaposed. The rice plant is short and the tillering is delayed or the number of tillers is reduced. After the end of labor, if the zinc deficiency is not serious, the symptoms can gradually disappear and resume normal growth, but the maturity period is prolonged. Zinc-deficient rice roots grow thin and have few new roots.
Maize is one of the most sensitive zinc field crops. In many parts of China, there are reports of zinc deficiency in maize. If the soil is deficient in zinc, “white seedling disease†occurs about ten days after emergence, that is, the chlorosis between young veins of newborns is pale yellow to pale white. Especially in the two-thirds of the base, the young leaves of the seedlings appear fine white spots and quickly expand to form partial white areas or necrotic patches, and the chlorophyll stripes of the leaves are translucent. Sometimes split along the stripe. Some leaf margins may also be necrotic. The sprouts are white, so zinc deficiency is sometimes referred to as "white bud disease." In addition to the above symptoms of new leaves, chlorotic stripes are also formed between old veins. Sometimes a broad yellow-to-yellow-band chlorotic zone is formed between the main vein and the leaf margin, mainly in the lower half of the leaf. In severe cases, it is tan and necrotic, the growth is hindered, the internodes become shorter, the fertility less, and the lack of grain and baldness.
Fruit trees such as apples, oranges, peaches, etc., in addition to chlorosis of leaves in the absence of zinc, the top of the branches tend to appear lobular growth, growth was "rosette-like", leaf mottled or "flower mosaic disease." Branches die when severe. Apples in northern China have zinc deficiency in the southern citrus.
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