Symptom Manifestations of Major Nutrient Element Deficiency and Excess in Cotton

I. Symptoms of Nitrogen Deficiency and Excess in Cotton

When cotton plants are deficient in nitrogen, the plants are short and lignified, the leaf color is yellow-green, the leaves become smaller, the petioles are shortened, there are few side branches, and the number of leaves is reduced. The lower leaves of the cotton plant are most obviously affected by nitrogen deficiency, the growing tip stops growing, and the number of flowers is small, often only the flowers and bolls on the first fruiting node of the lower fruiting branches open. In such cases, if nitrogen fertilizer is applied in time, the leaf color will turn green. When nitrogen deficiency is severe, the lower leaves turn yellow, then brown, and finally dry up and drop off; in addition, it can also cause young bolls to drop. In nitrogen-deficient cotton plants, although the root system develops better than the aboveground part, because vegetative growth is slow and boll setting is early, the yield is not high. Conversely, when nitrogen is supplied in excess, the cotton plants are tall, the field is severely shaded and crowded, boll shedding and square shedding are severe, the yield decreases, and fiber quality deteriorates.

II. Symptoms of Phosphorus Deficiency in Cotton

When cotton plants are deficient in phosphorus, the plants are short, the leaves are small, the leaf color is dark green, and maturity during the boll stage is delayed. When phosphorus deficiency is severe, the leaves turn purple, the red-green ratio of the stems and petioles is imbalanced, development is retarded, flowers and squares are prone to drop, few bolls mature, boll opening is delayed, the root system is poorly developed, and drought resistance is weak.

III. Symptoms of Potassium Deficiency in Cotton

When cotton plants are deficient in potassium, the plants are short, and the stems are thin and soft. The leaf color changes from pale yellow to dark green,   yellow-white patches appear between the veins and gradually turn brown, after which the entire leaf shrinks and becomes brittle.   The leaf margins turn reddish-brown and split, and the petioles may even drop off, sometimes rot, and curl downward. The leaves    turn reddish-brown, dry up, and fall early. In potassium-deficient cotton plants, the bolls are small and difficult to mature, and the fiber quality of the seeds and lint is reduced.

IV. Symptoms of Sulfur Deficiency in Cotton

When cotton plants are deficient in sulfur, both the aboveground and underground parts are short or stunted, the leaves are small and yellowish,   the chlorophyll between the veins disappears and later turns purple, while the veins remain green. These symptoms    first appear on young tender leaves, and the difference in root system formation compared with normal roots is especially obvious, with the lateral roots becoming shorter and smaller. Because the foundation for vegetative growth is weak, it often leads to few and small cotton bolls that are prone to drop.

V. Symptoms of Calcium in Cotton

When cotton is deficient in calcium during the growing period, the aboveground part is relatively short, the number of roots is small, and there are also very few lateral roots. The petioles of the lower leaves of cotton seedlings bend and droop, and often rot.

VI. Symptoms of Magnesium Deficiency in Cotton

When cotton plants are deficient in magnesium, the veins remain green, the areas between the veins are purplish-red, and the cotton bolls drop before maturing.     Magnesium deficiency symptoms often appear first on the lower leaves.

VII. Symptoms of Boron Deficiency and Excess in Cotton

When the soil is severely deficient in boron, it causes cotton to “have squares but no flowers”; the cotton seedlings may show the various symptoms above, the main manifestations being easy shedding of squares, no flowering and no boll setting, with symptoms appearing earliest on the leaves. When the soil is moderately or mildly deficient in boron, there may be a ring band on the petiole, which requires special attention during field diagnosis of cotton.

Conversely, when boron nutrition in cotton is excessive, the cotyledons are small, the margins wither and yellow and contract, forming spoon-shaped leaves that drop prematurely. The areas between the veins of the upper leaves become chlorotic, and brown   patches first appear on the margins of the lower old leaves; in severe cases the patches merge and extend toward the center of the leaf, causing the leaves to wither and drop,   and even the whole plant to die.

VIII. Symptoms of Zinc Deficiency in Cotton

When cotton plants are deficient in zinc, starting from the first true leaf, the young leaves take on a bronze color, with chlorosis between the veins, the leaves thicken and become brittle, the margins curl upward, and the internodes are short. The plants are small and appear clustered, and the growth period is delayed.

IX. Symptoms of Manganese Deficiency in Cotton

When cotton plants are deficient in manganese, chlorophyll formation is hindered, and chlorotic spots appear on the leaves.

X. Symptoms of Copper Deficiency in Cotton

When cotton plants are deficient in copper, the plants are thin and weak, the root system develops poorly, squares and bolls drop, and flowering or maturity is relatively late.