Iron deficiency is a common nutrient disorder, particularly in northern China, where calcareous or high-pH soils, especially saline soils, are prevalent. Iron plays a crucial role in chlorophyll synthesis, and when it's deficient, plants struggle to recycle the element, leading to visible symptoms. The primary signs of iron deficiency appear on young or upper leaves, starting with interveinal chlorosis—where the veins remain green while the rest of the leaf turns yellow. As the deficiency worsens, the leaves may turn light green, then grayish green, and eventually develop brown spots. In severe cases, the entire leaf becomes yellow, white, or falls off, and the growing tips may die, causing the plant to wilt.
In grasses and other cereal crops, iron deficiency is rare under normal field conditions. However, when it does occur, it is often due to interactions with other nutrients, such as excessive phosphorus. In these crops, new leaves tend to show early chlorosis with green veins, and severe deficiency can lead to complete yellowing or even death of the leaves. Dicotyledonous crops like soybeans are highly sensitive to iron deficiency. Since iron is a component of heme and nitrogenase, its lack reduces nitrogen fixation by Rhizobium bacteria, stunting plant growth. Early symptoms include yellowing of upper leaves with curled edges and green veins, which progress to yellowish-white leaves and, in extreme cases, necrotic brown spots along the leaf margins.
In southern China’s acid paddy fields, ferrous iron can become toxic, causing small brown spots between the veins of lower rice leaves. These spots spread from the tip toward the base, and the leaves may appear dark green, resembling potassium deficiency. Severe toxicity results in purple-brown or brownish-yellow leaves and black or rotting roots.
Zinc deficiency has also been widely reported in crops globally. Zinc is essential for auxin production, and its deficiency leads to stunted growth, shortened internodes, and distorted leaves. Symptoms typically start in new tissues, such as yellow or white chlorotic leaves with reduced growth, smaller fruits, and poor root development. In rice, zinc deficiency is most noticeable during the seedling stage, especially in calcareous or saline soils. Affected seedlings develop narrow, white leaves and are referred to as "dwarf seedlings." Severe cases can result in dead seedlings, giving the field a patchy, reddish appearance. Leaves show chlorotic stripes, brown spots, and brittle veins. Root growth is also affected, with thin, sparse roots.
Maize is highly susceptible to zinc deficiency, and "white seedling disease" occurs about 10 days after emergence. Young leaves display pale yellow or white interveinal chlorosis, with white spots that expand into necrotic areas. The leaves may split along the stripes, and in severe cases, the plant becomes stunted, with reduced grain fill and baldness.
Fruit trees like apples, oranges, and peaches also suffer from zinc deficiency, showing leaf chlorosis and abnormal growth patterns, such as rosette-like branches or mottled leaves. Severe cases can lead to branch dieback. In northern China, apple trees and citrus trees are commonly affected.
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