Iron deficiency is a common nutrient disorder, particularly prevalent in northern China, especially in calcareous or high-pH soils, and in saline areas. Iron plays a crucial role in chlorophyll synthesis, and when plants lack this essential element, they struggle to reutilize iron, leading to visible symptoms. The primary signs of iron deficiency appear on the younger or upper parts of the plant, with the veins remaining green while the rest of the leaf turns yellow—this condition is known as chlorosis. As the deficiency worsens, the leaves may shift from light green to grayish green, and brown spots might develop. In severe cases, the entire leaf can turn pale, yellow, or even fall off, and the tender shoots may die, causing the plant tips to wither.
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 an excess of phosphorus. In these cases, new leaves are the first to show chlorosis, with green veins and gradually turning entirely yellow. Affected leaves tend to dry out and become brittle. Dicotyledonous plants like soybeans are particularly vulnerable. Since iron is a key component of heme and nitrogenase, its deficiency reduces the ability of Rhizobium to fix nitrogen, stunting plant growth. Early symptoms include yellowing of the upper leaves with slightly curled edges and green veins. As the condition progresses, the leaves may turn pale yellow or white, and in extreme cases, brown necrotic spots appear along the leaf margins.
In acid paddy fields in southern China, ferrous iron (Fe²âº) can be toxic. Symptoms include small brown spots between the veins of the 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, with blackened or rotten roots.
Zinc deficiency has also gained attention in recent years, both domestically and internationally. Zinc is vital for auxin production, and its deficiency leads to stunted growth, shortened internodes, and impaired leaf expansion. Leaves may become distorted, wrinkled, or develop brown spots between the veins. The first signs typically appear in young tissues, such as new leaves turning grayish green or yellow-white, with delayed development, smaller fruits, and poor root growth.
In rice, zinc deficiency is most evident during the seedling stage. It commonly occurs in calcareous and coastal saline soils in China. Symptoms usually appear about two weeks after transplanting, becoming most noticeable at the time of tillering. Leaves turn white and narrow, and the seedlings become weak, hence the term "dwarf seedlings." Severe cases result in dead seedlings, giving the field a patchy, reddish appearance—sometimes called "red seedlings." When the plant has 5–6 leaves, the base of the new leaves turns white, while older leaves show chlorotic stripes along the main veins. Brown spots may form on the midribs, spreading into round or oval lesions. Similar symptoms can appear on sheaths and stems in advanced stages. The lower leaves become brittle and break easily, and the spacing between leaf sheaths decreases. Rice plants are short, and tillering is delayed or reduced. If the deficiency isn't severe, symptoms may fade over time, though maturity is prolonged. Root growth is also affected, with thin and sparse roots.
Maize is highly sensitive to zinc deficiency. In many regions of China, "white seedling disease" is observed about ten days after emergence, characterized by pale yellow to white chlorosis between the young leaf veins. White spots appear on the base of the leaves and quickly expand into large necrotic areas. The leaves display translucent chlorotic stripes, sometimes splitting along them. Necrosis may also occur at the leaf margins. Due to the white coloration, this condition is also called "white bud disease." Chlorotic bands may also form between older veins, and in severe cases, the internodes shorten, leading to poor grain filling and baldness.
Fruit trees such as apples, oranges, and peaches exhibit similar symptoms when zinc-deficient. In addition to leaf chlorosis, the top of branches may grow abnormally, forming a rosette-like pattern. Leaves may show mottling or a "flower mosaic" appearance, and severe cases can lead to branch dieback. In northern China, apple trees and citrus in the south are particularly prone to zinc deficiency.
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