What are the typical symptoms of nitrogen, phosphorus, and potassium deficiency in rapeseed?

Rapeseed is a very important oil crop and also has a certain ornamental value; a field of rapeseed flowers looks golden and is very beautiful and attractive. During rapeseed cultivation, if the corresponding elements are lacking, some symptoms will appear, leading to reduced yield and reduced quantity. Let us take a look below at what typical symptoms rapeseed shows when lacking nitrogen, phosphorus, potassium, and other elements?

1. Phosphorus deficiency

Phosphorus has an important function in genetic variation; phosphorus participates in the metabolism and transport of carbohydrates; phosphorus plays an important role in nitrogen metabolism; it improves the plant's ability to resist drought, cold, disease, lodging, and acid and alkali; it promotes plant growth and development, promotes flower bud differentiation and shortens the time for flower bud differentiation, and promotes crops to bloom earlier and mature earlier.

When rapeseed lacks phosphorus, the plant grows slowly and is short, with 2~3 fewer leaves than a normal plant, and the leaves are thick and small; the leaf color is dark green or grayish green and lacks luster; the petioles are purple, and the leaf edges have purplish red spots or patches, while the lower leaves turn yellow and fall off; the root system develops poorly, bolting is slow, and the bolting color turns red.

2. Nitrogen deficiency

Nitrogen is a main component of proteins, nucleic acids, and phospholipids; nitrogen plays an important role in material and energy metabolism; nitrogen regulates life activities; nitrogen is a component of chlorophyll and is closely related to photosynthesis.

Nitrogen deficiency in rapeseed appears as poor growth vigor and short plants. First, the old leaves turn red, and then it gradually develops toward the new leaves, chlorophyll decreases, and they take on a yellow color. If seedlings encounter drought and fertilizer loss, red leaves are likely to appear; if nitrogen is deficient in the middle and late stages, branching decreases, the number of siliques and filled grains drops sharply, grain weight decreases, and yield declines noticeably.

3. Magnesium deficiency

Magnesium is a component of chlorophyll and phytin. The main symptom of magnesium deficiency in rapeseed is leaf chlorosis, with the old leaves at the base beginning to turn yellow. Especially during the bolting stage, a large amount of magnesium is needed; otherwise, it will cause physiological diseases such as short plants.

4. Potassium deficiency

Potassium is an activator of enzymes. When rapeseed lacks potassium, it appears as chlorosis and yellowing of the mesophyll at the seedling stage, leaves shrink, thicken, and become smaller, leaf veins become noticeably darker, and growth is slow. In severe potassium deficiency, the heart leaves shrink and die, and at flowering the leaf edges scorch and curl, the leaf surface is uneven, and the texture is brittle, hard, and easy to break. At the pod-setting stage, plants appear short, with few branches, few siliques, and many empty pods, resulting in reduced yield.

5. Zinc deficiency

When rapeseed lacks zinc, it first starts from the leaf margins, where the leaf color fades and turns grayish white, then develops toward the middle of the leaf, showing yellow-white irregular lesions without necrosis. Both sides of the leaf veins still remain green, and the outer edges of the diseased leaves do not show shrinkage. In severe cases, the outer edges of the diseased leaves in the middle and lower parts curl outward, and the leaf tips droop downward. When zinc is deficient in the middle and late stages, the mesophyll first shows small white spots or yellow-white spots, and the lesions continuously expand, with the whole leaf turning yellow-white or scorched yellow, but both sides of the leaf veins still remain green; in severe cases, the leaves of the whole plant lose green.

6. Sulfur deficiency

The symptoms of sulfur deficiency in rapeseed are basically similar to those of nitrogen deficiency: seedlings are narrow, small, and yellowed, leaf veins lack green, and later this gradually spreads over the whole leaf and onto the stems and inflorescences at the bolting and flowering stages; pale yellow flowers often turn white, flowering continues without stopping, and at the mature stage, besides mature and immature siliques, there are still flowers and flower buds on the plant. The tips of the siliques are shriveled, and about half of the seeds are poorly developed. The plants are short, and the stems are prone to lignification or breaking.