Introduction

Identifying the lack of nutrients needed by the rapeseed plant in time is one of the ways to prevent its performance from decreasing. Determining the fertilizer requirement of the plant, through the apparent detection of deficiencies after its symptoms appear in the field, is not the only method and not necessarily the best method, but more reliable solutions can be adopted through soil testing and plant tissue analysis. Observational symptoms in the field can be used as a supplement to detect food shortages and prevent the aggravation or repetition of shortages. Also, it is better to use fertilizer based on all available information. If stressors such as drought, disease, or chemical injury are combined, it may be difficult to accurately diagnose food shortages. In this article, the symptoms of nutrient deficiency in young rapeseed plants have been discussed.

Canola

The main nutritional requirements of the rapeseed plant

Compared to many other crops, rapeseed needs more nutrients to produce high yields, so compared to wheat, it needs 25% more nitrogen, phosphorus and potassium, and more than 2 times more sulfur than wheat. The process of canola’s need for nutrients intensifies and increases from the 5-leaf stage onwards, it reaches a maximum during flowering and continues with an almost constant trend until the seed ripens.

1- Nitrogen

Nitrogen deficiency is the most common type of nutrient deficiency in rapeseed plants, especially in wet and cold conditions. Since nitrogen is mobile within the plant, symptoms of nitrogen deficiency first appear in the oldest leaves. The first signs of nitrogen deficiency are growth reduction and the leaf color changes from dark green to pale green (Figure 1(a)). They do not open and widen to form the normal shape of the plant. Nitrogen-deficient plants are smaller and their older leaves turn purple. The color change starts from the upper surface of the leaves.

Figure 1- (A) – Symptoms of nitrogen deficiency in the early stages of growth, (B) – The appearance of purple color in the tip and upper surface margin of older leaves as a result of nitrogen deficiency, (C) – The spread of purple color from the tip of the leaf to the end of the leaf in older leaves. As a result of nitrogen deficiency, (d)- plants with severe nitrogen deficiency with leaves that are arranged in a vertical pile and the appearance of purple and pink pigments on the upper and lower surfaces of older leaves, (e)- nitrogen deficiency in the youngest to the oldest leaves, There are no signs of deficiency in young leaves, older leaves turn purple and yellow, (j)- Nitrogen deficiency in an established plant, older leaves turn yellow, and their yellowing starts from the margin and progresses towards the center of the leaf.

In older leaves, the veins on the upper surface of the leaf and the edge of the leaf turn purple, and the tail of the leaf also becomes pale purple (Figure 1 (b). As the leaves age, both the upper and lower surface of the leaf have a purple color from the tip to the side. The end of the leaf expands. As a result, half of the leaf turns purple and the other half turns pale green (Figure 1 (c). Over time, the entire surface of the leaf turns purple, then for a short time, it turns pink (Figure 1 (d)). The speed turns yellow (Figure 1(e)) and detaches from the plant. Young leaves remain green for a longer time than older leaves, but their size is smaller compared to the leaves of plants that are not deficient in nitrogen. New leaves are small. They are, but they do not show any signs of deficiency.

Leaf yellowing in the oldest leaves starts from the edge of the leaf, gradually spreads between the veins towards the main vein and finally covers the entire surface of the leaf. Then the main vein changes color from green to yellow with brown edges and finally the leaf is separated from the plant (Figure 1(j)). Since nitrogen fertilizers are completely soluble, nitrogen deficiency in the early stages of growth can be easily solved by using urea fertilizer. It is recommended to consume one-third of the nitrogen fertilizer needed by rapeseed (about 100 kg of urea fertilizer) in autumn and in the early stages of growth. To reduce fertilizer wastage, it is better to consume this amount after the first irrigation and with the second or third irrigation. Also, if there is a deficiency and to prevent its aggravation and further weakening of the plant, it is possible to use urea spraying with a concentration of 5% in accordance with the spraying requirements.

2- Phosphorus

In phosphorus deficiency, the growth of shoot is severely affected and limited from the beginning. Phosphorus-deficient plants have the same shape and color as healthy plants, and the only difference is that phosphorus-deficient plants are smaller. Therefore, it is very difficult to detect phosphorus deficiency based on external signs, unless the growth of plants is compared with healthy plants located near them (Figure 2(a)).

Figure 2_Rose

Figure 2- (a) Phosphorus deficiency in the early stages of growth. The only sign of deficiency is growth retardation. (b) Deficient plants have the same color and shape as healthy plants, (c) In the case of severe phosphorus deficiency, a purple band is formed on the edge of the older leaves, (d) The oldest leaves are purple just before they are separated from the plant and then They turn bronze.

Phosphorus deficient leaves are much smaller in size, but in terms of shape and color they are not different from healthy leaves (Figure 2 (b)). In case of continued and severe phosphorus deficiency in most of the leaves, a narrow purple border will be formed (Figure 2 (c)). In older leaves, the entire surface of the leaf becomes purple and then bronze, these leaves later turn yellow and then separate from the plant (Figure 2(d)).

Phosphorus deficiency in the early stages of growth can be used with fertilizers such as monoammonium phosphate in the amount of 50 kg per hectare. If rapeseed irrigation is done through the rain irrigation system or bWorse, phosphorus deficiency can be easily compensated by consuming 10 kg of urea phosphate per hectare.

3- Potassium

Potassium deficiency is very obvious in rapeseed, but in very young plants, reduced shoot growth is the only major symptom. In the next stages of growth and aging of the plant, specific signs of potassium deficiency are revealed. The first sign of potassium deficiency is the imperceptible paleness between the veins, which occurs on the surface of older leaves. Over time, the paleness becomes more obvious and is more intense at the edge of the leaf, while it becomes less toward the central part and the main vein of the leaf. The veins and surrounding tissue remain green (Figure 3(a)).

Figure 3_Rose

Figure 3- (a) Inconspicuous paleness of the leaf margin and between the veins as the first signs of potassium deficiency, (b) paleness in the middle parts of the leaf and white necrotic spots as a result of potassium deficiency, (c) with the passage of time, the pale parts between the veins gradually fade. They die and disappear. (d) severe symptoms of potassium deficiency in rapeseed, the main veins and secondary veins turn dark green, while most of the leaf parts are necrotic.

The pale parts gradually disappear and create white to pale pink male spots on the surface of the leaf (Figure 3(b)). Finally, these dead spots (necrosis) all over the outer edge of the leaf are connected to each other and turn brown. Around the main and secondary veins remain dark green (Figure 3 (c)). Potassium deficiency does not cause purple leaves. These parts become very dry and thin and finally become white and dry. Veins and their adjacent tissue remain green.

In case of potassium deficiency and deficiency symptoms appear (Figure 4(d)), if the irrigation water and agricultural soil do not have salinity problems, the consumption of 25 kg per hectare of potassium chloride fertilizer can eliminate the potassium deficiency. But if there is a risk of water and soil salinity, it is better to dissolve 10 to 20 kg of Soluptas in irrigation water and use it through the rain or drip irrigation system or sprinkle it with a concentration of 5 per thousand. Also, potassium nitrate fertilizer is suitable for soil use and foliar application, and foliar application of 3 per thousand potassium nitrate will eliminate the deficiency.

4- Sulfur

The lack of sulfur changes the shape and structure of rapeseed leaves more than the lack of other elements. At first, the growth of aerial parts is reduced, without any signs of color change. With the growth and age of the plant, the symptoms become more specific (Figure 4(a)).

Figure 4-(a) Symptoms of sulfur deficiency in the early to middle stages of rapeseed growth, the decrease in the growth of aerial parts is the first sign. New leaves become pale and eventually purple in color and markedly deformed, (b) bright green color of new leaves in a sulfur-deficient plant. The margin of the new leaf is strongly serrated, which continues to the petiole, (c) formation of a pale purple color in the upper part of the leaf due to sulfur deficiency, (d) healthy leaf (right) compared to leaves with severe sulfur deficiency. Deficient leaves are twisted and tube-shaped, pale green on the upper surface and deep purple with white veins on the lower surface. The upper surface tends to be pale green and shows a faint purple, while the underside of the leaf becomes distinctly purple. The lower surface of the leaves is purple and the veins are white.

New leaves are pale green and much thicker than healthy young leaves. The margin of deficient leaves is strongly wavy and jagged compared to healthy leaves (Figure 4(b)). In fully opened leaves, a faint purple border may appear on the upper surface of the leaf (Figure 4 (c)). With the passage of time and increasing severity of sulfur deficiency, a very bright purple color is formed on the lower surface of the leaf. The thickening of the leaves continues, the edge of the leaf bends inward and the leaf becomes tubular (Figure 4 (d)). In sulfur-deficient plants, the leaves are placed horizontally and the plants spread out on the ground, while in natural plants, the leaves are more upright and the plant has a dome shape (Figure 4(e)). In very severe sulfur deficiency, the leaf is folded upwards along the middle vein and a deep purple color is formed on the lower surface of the leaf (Figure 4(j)). Although the rapeseed plant needs a lot of sulfur, because sulfate is the dominant anion in the cultivated trees of the province, sulfur deficiency rarely occurs in rapeseed. However, in case of sulfur deficiency, it is suitable to use liquid sulfur, bentonite sulfur (together with Thiobacillus) or organic sulfur. Of course, using sulfate-based fertilizers such as ammonium sulfate or potassium sulfate will also be effective.

Rapid diagnosis of the lack of main nutrients (high consumption)

In order to quickly detect the lack of the main nutritional elements of the rapeseed plant, there are signs that can be taken as soon as they are observed in the field:

Nitrogen

• Deficient plants are smaller.
• Young and growing leaves are narrower and more upright.
• In older leaves, the veins and the surface of the leaf become purple, the appearance of purple color starts from the tip of the leaf and the valley extends to the base of the leaf and the main petiole on both the upper and lower surfaces.
• The color of the leaf changes to pink and yellow and the leaf dies.

phosphorus

• Deficient plants are smaller, but the shape of the leaves is unchanged.
• In severely deficient plants, the leaf margins turn purple, which may occur in all leaves.
• In old and dying leaves, the purple color is observed on the entire surface of the leaf, which then turns bronze.

Potassium

• Swollen intervenous tissue