Symptoms of Nutrient Deficiency in Rapeseed and Remedial Measures
Nutrient Deficiency in Rapeseed and Its Remedial Measures
(Agricultural Wealth Network) During its growth and development, rapeseed needs to absorb a variety of nutrient elements. Once a certain element is deficient, the plant will show corresponding deficiency symptoms through its external morphology, and in production this is mostly used as the basis for diagnosing nutrient deficiencies and taking remedial measures.
Nitrogen Deficiency Nitrogen is the element required in the largest amount for rapeseed growth and development. When nitrogen is deficient, the plants grow thin and weak, with few and small leaves that are yellow-green to yellow; the edges of some lower stem leaves turn red, and this gradually spreads to the leaf veins; the number of effective branches and siliques is greatly reduced, the 1000-grain weight also decreases accordingly, and yield drops significantly. Remedial measures: for nitrogen deficiency at the seedling stage, apply 15-25 kg of ammonium bicarbonate per mu in furrows as a topdressing, or apply 750-1000 kg of human and animal manure diluted with water; for nitrogen deficiency at the later stage, spray the leaves with a 1%-2% urea solution.
Phosphorus Deficiency Rapeseed is a phosphorus-loving crop, and its phosphorus requirement is more than double that of cereal crops. When phosphorus is deficient, the plants are short, grow slowly, leaf emergence is delayed, leaf area is small, leaf color is dark green and lacks luster, purple-red spots or patches appear at the edges, and the petioles and veins on the underside of the leaves turn purple-red; root development is poor, the number of siliques and the 1000-grain weight are significantly reduced, and the oil content decreases. In addition, according to water culture experiments, if phosphorus deficiency begins after the true leaves of rapeseed appear, the plants have few and small leaves, can only bolt, and cannot set seed, resulting in a complete loss of harvest; if phosphorus deficiency begins at the five-leaf stage, yield decreases to only 0.44% of that under normal phosphorus nutrition; if phosphorus deficiency begins at the ten-leaf stage, yield rises markedly, reaching 27.8% of that under normal phosphorus nutrition. Remedial measures: for phosphorus deficiency at the seedling stage, apply 25-30 kg of superphosphate per mu in furrows as a topdressing or diluted with water, and the earlier the effect, the better; at the later stage, spray the leaves with a 1% superphosphate extract.
Potassium Deficiency Potassium has a marked effect on the growth and development, dry matter accumulation, yield, and quality of rapeseed. When potassium is deficient, the plants tend to wilt, the seedlings appear prostrate, and the areas between the veins bulge upward, causing the leaves to curve in an arch shape; leaf color becomes darker, usually dark blue-green, and the leaf margins or interveinal areas lose green, initially often as spots the size of a needle tip, and finally necrotic patches develop; in severe potassium deficiency the leaves wither completely but do not fall off. In addition, according to observations by the Oil Crops Research Institute of the Chinese Academy of Agricultural Sciences, under conditions of extreme potassium deficiency, compared with rapeseed supplied with normal potassium, the period from emergence to the ten-leaf stage is delayed by about 7 days, and the appearance of the bud-bolting stage is delayed by about 20 days; plants with extreme potassium deficiency begin to die at the flowering stage. Remedial measures: for potassium deficiency at the early stage, apply 7-10 kg of potassium chloride or 75-100 kg of plant ash per mu in furrows as a topdressing; at the later stage, spray the leaves with a 0.1%-0.2% monopotassium phosphate solution.
Magnesium Deficiency When rapeseed is deficient in magnesium, mottled patches of yellow-purple and green-purple appear on the leaf surface. Remedial measures: upon finding magnesium deficiency, promptly spray the leaves with a 1%-2% magnesium sulfate solution.
Sulfur Deficiency When rapeseed is deficient in sulfur, the plants are short and light green, very similar to nitrogen deficiency; larger notches appear at the leaf margins, and the leaves wrinkle into a cup shape, while the underside of the leaves, the veins, and the stems turn purple-red. Remedial measures: together with intertillage, broadcast 1-2 kg of sulfur powder per mu, or 50 kg of gypsum powder. In addition, appropriately increasing the application of sulfur-containing fertilizers such as ammonium sulfate also has a good effect.
Boron Deficiency Rapeseed is a boron-loving crop, and the boron content in its dry matter is 32.5-36 times higher than that of gramineous crops such as wheat and rice; generally, when many plants in the field show boron deficiency symptoms, yield is reduced by at least 20%-30%, and in severe cases there is almost no harvest. Its symptoms vary greatly depending on the degree of boron deficiency: in severe cases the plants wither and die at the seedling stage, while in mild cases symptoms appear only after flowering. Diseased plants have poor root development, fibrous roots do not grow long, the epidermis turns brown, and some root crowns swell and the cortex cracks. The leaves first turn dark green, become smaller in shape, thicker and more brittle in texture, with the leaf tips curling backward and the surface wrinkled and uneven. Subsequently, the margins of the middle and lower leaves turn purple and spread inward, then turn blue-purple; the veins and nearby tissues turn yellow, resulting in patches of blue-purple. Finally, part of the leaf margins die, the entire leaf turns yellow, and it falls off early. After bolting, the growing point shrinks or dies, the embryonic stem splits, the vascular system and fertilization are disrupted, carbohydrates remain trapped in the leaves, flowering is slow, the inflorescence is shortened, small branches cluster, and flowering does not set seed (commonly known as "flowers but no seed") or the grains are not plump, and at maturity the siliques are as short as radish pods. The silique skins and stem epidermis turn purple-red or blue-purple, longitudinal cracks appear in the cortex of the middle and lower parts of the stems, and split patches appear on the upper parts. Prevention and remedial measures: 1. For soil with severe boron deficiency, apply 0.5-1 kg of borax per mu as a base fertilizer during land preparation; for rapeseed grown by seedling raising and transplanting, apply 15-25 kg of boron-magnesium fertilizer per mu before transplanting, with good results. 2. At the seedling stage, before bolting, at the initial flowering stage, or when boron deficiency is found in the plants, spray the leaves with a 0.1%-0.2% borax solution.
Manganese Deficiency When rapeseed is deficient in manganese, the plants are short and show chlorosis, young leaves are yellow-white with green veins, stem growth is weak and yellow-green and mostly woody, and the number of flowers and seeds is reduced. Remedial measures: upon finding manganese deficiency, promptly spray the leaves with a 0.1%-0.2% manganese sulfate solution.
Zinc Deficiency When rapeseed is deficient in zinc, chlorosis begins at the leaf margins, the leaf color fades to gray-white, and then spreads toward the middle, with the leaf mesophyll showing yellow patches. The leaf margins of diseased leaves do not wrinkle, and the more severely whitened leaves in the middle and lower parts curl outward, with the leaf tips drooping. Prevention and remedial measures: at the seedling stage, apply 0.5-0.75 kg of zinc sulfate per mu in furrows as a topdressing; when zinc deficiency symptoms appear in the plants, spray the leaves with a 0.2% zinc sulfate solution.
Molybdenum Deficiency When rapeseed is deficient in molybdenum, the leaves wilt or scorch, usually twisting spirally, the old leaves thicken, and the plants become clustered. Remedial measures: upon finding molybdenum deficiency, promptly spray the leaves with a 0.01%-0.1% ammonium molybdate solution.
Nitrogen Deficiency Nitrogen is the element required in the largest amount for rapeseed growth and development. When nitrogen is deficient, the plants grow thin and weak, with few and small leaves that are yellow-green to yellow; the edges of some lower stem leaves turn red, and this gradually spreads to the leaf veins; the number of effective branches and siliques is greatly reduced, the 1000-grain weight also decreases accordingly, and yield drops significantly. Remedial measures: for nitrogen deficiency at the seedling stage, apply 15-25 kg of ammonium bicarbonate per mu in furrows as a topdressing, or apply 750-1000 kg of human and animal manure diluted with water; for nitrogen deficiency at the later stage, spray the leaves with a 1%-2% urea solution.
Phosphorus Deficiency Rapeseed is a phosphorus-loving crop, and its phosphorus requirement is more than double that of cereal crops. When phosphorus is deficient, the plants are short, grow slowly, leaf emergence is delayed, leaf area is small, leaf color is dark green and lacks luster, purple-red spots or patches appear at the edges, and the petioles and veins on the underside of the leaves turn purple-red; root development is poor, the number of siliques and the 1000-grain weight are significantly reduced, and the oil content decreases. In addition, according to water culture experiments, if phosphorus deficiency begins after the true leaves of rapeseed appear, the plants have few and small leaves, can only bolt, and cannot set seed, resulting in a complete loss of harvest; if phosphorus deficiency begins at the five-leaf stage, yield decreases to only 0.44% of that under normal phosphorus nutrition; if phosphorus deficiency begins at the ten-leaf stage, yield rises markedly, reaching 27.8% of that under normal phosphorus nutrition. Remedial measures: for phosphorus deficiency at the seedling stage, apply 25-30 kg of superphosphate per mu in furrows as a topdressing or diluted with water, and the earlier the effect, the better; at the later stage, spray the leaves with a 1% superphosphate extract.
Potassium Deficiency Potassium has a marked effect on the growth and development, dry matter accumulation, yield, and quality of rapeseed. When potassium is deficient, the plants tend to wilt, the seedlings appear prostrate, and the areas between the veins bulge upward, causing the leaves to curve in an arch shape; leaf color becomes darker, usually dark blue-green, and the leaf margins or interveinal areas lose green, initially often as spots the size of a needle tip, and finally necrotic patches develop; in severe potassium deficiency the leaves wither completely but do not fall off. In addition, according to observations by the Oil Crops Research Institute of the Chinese Academy of Agricultural Sciences, under conditions of extreme potassium deficiency, compared with rapeseed supplied with normal potassium, the period from emergence to the ten-leaf stage is delayed by about 7 days, and the appearance of the bud-bolting stage is delayed by about 20 days; plants with extreme potassium deficiency begin to die at the flowering stage. Remedial measures: for potassium deficiency at the early stage, apply 7-10 kg of potassium chloride or 75-100 kg of plant ash per mu in furrows as a topdressing; at the later stage, spray the leaves with a 0.1%-0.2% monopotassium phosphate solution.
Magnesium Deficiency When rapeseed is deficient in magnesium, mottled patches of yellow-purple and green-purple appear on the leaf surface. Remedial measures: upon finding magnesium deficiency, promptly spray the leaves with a 1%-2% magnesium sulfate solution.
Sulfur Deficiency When rapeseed is deficient in sulfur, the plants are short and light green, very similar to nitrogen deficiency; larger notches appear at the leaf margins, and the leaves wrinkle into a cup shape, while the underside of the leaves, the veins, and the stems turn purple-red. Remedial measures: together with intertillage, broadcast 1-2 kg of sulfur powder per mu, or 50 kg of gypsum powder. In addition, appropriately increasing the application of sulfur-containing fertilizers such as ammonium sulfate also has a good effect.
Boron Deficiency Rapeseed is a boron-loving crop, and the boron content in its dry matter is 32.5-36 times higher than that of gramineous crops such as wheat and rice; generally, when many plants in the field show boron deficiency symptoms, yield is reduced by at least 20%-30%, and in severe cases there is almost no harvest. Its symptoms vary greatly depending on the degree of boron deficiency: in severe cases the plants wither and die at the seedling stage, while in mild cases symptoms appear only after flowering. Diseased plants have poor root development, fibrous roots do not grow long, the epidermis turns brown, and some root crowns swell and the cortex cracks. The leaves first turn dark green, become smaller in shape, thicker and more brittle in texture, with the leaf tips curling backward and the surface wrinkled and uneven. Subsequently, the margins of the middle and lower leaves turn purple and spread inward, then turn blue-purple; the veins and nearby tissues turn yellow, resulting in patches of blue-purple. Finally, part of the leaf margins die, the entire leaf turns yellow, and it falls off early. After bolting, the growing point shrinks or dies, the embryonic stem splits, the vascular system and fertilization are disrupted, carbohydrates remain trapped in the leaves, flowering is slow, the inflorescence is shortened, small branches cluster, and flowering does not set seed (commonly known as "flowers but no seed") or the grains are not plump, and at maturity the siliques are as short as radish pods. The silique skins and stem epidermis turn purple-red or blue-purple, longitudinal cracks appear in the cortex of the middle and lower parts of the stems, and split patches appear on the upper parts. Prevention and remedial measures: 1. For soil with severe boron deficiency, apply 0.5-1 kg of borax per mu as a base fertilizer during land preparation; for rapeseed grown by seedling raising and transplanting, apply 15-25 kg of boron-magnesium fertilizer per mu before transplanting, with good results. 2. At the seedling stage, before bolting, at the initial flowering stage, or when boron deficiency is found in the plants, spray the leaves with a 0.1%-0.2% borax solution.
Manganese Deficiency When rapeseed is deficient in manganese, the plants are short and show chlorosis, young leaves are yellow-white with green veins, stem growth is weak and yellow-green and mostly woody, and the number of flowers and seeds is reduced. Remedial measures: upon finding manganese deficiency, promptly spray the leaves with a 0.1%-0.2% manganese sulfate solution.
Zinc Deficiency When rapeseed is deficient in zinc, chlorosis begins at the leaf margins, the leaf color fades to gray-white, and then spreads toward the middle, with the leaf mesophyll showing yellow patches. The leaf margins of diseased leaves do not wrinkle, and the more severely whitened leaves in the middle and lower parts curl outward, with the leaf tips drooping. Prevention and remedial measures: at the seedling stage, apply 0.5-0.75 kg of zinc sulfate per mu in furrows as a topdressing; when zinc deficiency symptoms appear in the plants, spray the leaves with a 0.2% zinc sulfate solution.
Molybdenum Deficiency When rapeseed is deficient in molybdenum, the leaves wilt or scorch, usually twisting spirally, the old leaves thicken, and the plants become clustered. Remedial measures: upon finding molybdenum deficiency, promptly spray the leaves with a 0.01%-0.1% ammonium molybdate solution.