What are the common symptoms of nutrient imbalance in tomatoes?

Tomato (Lycopersicon esculentum), also known as the tomato plant, has fruit used as a vegetable or fruit and is an important source of vitamin C for humans.
The tomato stem is trailing or semi-upright, and the inflorescence is a cyme or raceme; the fruit matures 40 to 50 days after flowering. Tomato is a warm-season crop and is not tolerant of frost. The optimum temperature for stem and leaf growth is 20 to 25°C, and during the fruiting period a daytime temperature of 25 to 28°C and a nighttime temperature of 16 to 20°C are suitable. A nighttime temperature below 15°C or above 30°C will hinder normal fertilization and cause flower drop; a temperature below 7°C during the flower bud stage causes deformed fruit; tomato is not sensitive to day length, and if the temperature is suitable it can be cultivated in all four seasons. Tomato has a relatively wide adaptability to soil. However, its tolerance to waterlogging is weak, and soil that alternates between dry and wet easily causes cracked fruit. Tomato requires 60 to 90 days of seedling raising before transplanting. The planting density is about 2000 to 4000 plants per mu.
Tomato is currently one of the main vegetables grown under protected cultivation. Because tomato flowers and sets fruit while growing stems and leaves, coordinating vegetative growth and reproductive growth is the key to a high yield.
　　
Symptoms of nutrient imbalance in tomatoes:
Tomato has a relatively high demand for nutrients throughout its life, and only when all nutrients are sufficient can the yield and quality of the fruit be guaranteed. Nutrient imbalance will cause symptoms of poor growth.
Nitrogen is an important substance for the formation of proteins, chlorophyll, and so on in tomato; when nitrogen is insufficient, the whole plant is stunted and weak, the leaves fade in color, and the fruit is small with low yield; when nitrogen is excessive, vegetative growth is excessive, the fruit-setting rate is low, the ability to resist pests and diseases declines, the fruit is not resistant to pressure and has a short fresh-keeping period. The fruit symptoms of excessive nitrogen are similar to those of potassium deficiency, and potassium fertilizer can be used to correct the symptoms of excessive nitrogen.
Phosphorus participates in many key physiological processes of tomato. Phosphorus exists in all living cells, and its role in root development and the fruit ripening process is irreplaceable; when tomato seedlings are deficient in phosphorus, growth stagnates, the underside of the leaves turns purplish red, mature leaves turn grayish green, buds and flowers easily drop, and leaf curling appears later.
Potassium is an important quality element for tomato. Potassium increases the sweetness of the fruit and reduces the invasion of crop diseases; potassium can increase the flowering and fruit-setting rate of tomato and also has a flower-forcing effect, advancing flowering and fruiting, advancing maturity, and has an obvious effect in extending the fresh-keeping period of the fruit. When potassium is insufficient, the leaf margins of the lower leaves of tomato curl and yellow-wilt, with grayish white spots, and potassium-deficient fruit shows “green back disease.”
Tomato deficient in calcium is prone to blossom-end rot. At first, the flesh near the blossom end of the fruit appears water-soaked and necrotic, the diseased tissue collapses, and then blackens, shrinks, and sinks; generally the fruit does not drop.
Tomato is sensitive to magnesium deficiency. With magnesium deficiency, chlorotic yellow spots appear between the veins of the lower leaves, the leaf margins turn various colors such as orange, red, and purple, and the fruit also fades from red to pale orange, with reduced stickiness of the flesh.
With sulfur deficiency in tomato, the areas between the leaf veins turn yellow, the petioles and stems turn red, the internodes shorten, and the leaves become smaller. The overall plant color fades, appearing light green or yellow-green.
With manganese deficiency in tomato, the green between the veins of new leaves fades and turns yellow, while the veins remain green and the vein pattern is relatively clear; severe manganese deficiency produces grayish white or brown spots.
With iron deficiency in tomato, yellow-white discoloration first appears on the terminal buds and new leaves, with green remaining along the leaf veins, and the leaves become thinner; generally there is no browning or necrosis, and grayish yellow spots also appear at the base of the leaves.
With zinc deficiency in tomato, the small leaves are clustered, yellow spots appear on the new leaves, and the yellow spots gradually spread to the whole leaf; the plant is also easily infected by viral diseases.
Sensitivity to copper deficiency in tomato is manifested as terminal yellowing disease.
With boron deficiency in tomato, rust spots appear on the fruit surface; with boron deficiency in tomato, the terminal bud stops growing, the fruit skin and flesh become necrotic and corky, flowers form but no fruit sets, and rust spots easily appear on the fruit surface.
With molybdenum deficiency in tomato, during the true leaf stage the leaves turn yellow and curl, the new leaves are mottled, the chlorotic parts arch upward, the small leaflets curl upward, and finally the tips and margins of the small leaflets shrivel and die.
With chlorine deficiency in tomato, the leaf tips of the lower leaves wilt and become narrow, growth is inhibited, and even necrosis occurs; the roots shorten and thicken, and growth is inhibited.
Based on external symptoms, it is possible to make a preliminary judgment of whether tomato is deficient in a nutrient and the degree of the deficiency.
　　
Potassium is an important quality element for tomato. Potassium increases the sweetness of the fruit and reduces the invasion of crop diseases; potassium can increase the flowering and fruit-setting rate of tomato and also has a flower-forcing effect, advancing flowering and fruiting, advancing maturity, and has an obvious effect in extending the fresh-keeping period of the fruit. When potassium is insufficient, the leaf margins of the lower leaves of tomato curl and yellow-wilt, with grayish white spots, and potassium-deficient fruit shows “green back disease.”
Tomato deficient in calcium is prone to blossom-end rot. At first, the flesh near the blossom end of the fruit appears water-soaked and necrotic, the diseased tissue collapses, and then blackens, shrinks, and sinks; generally the fruit does not drop.
With zinc deficiency in tomato, the small leaves are clustered, yellow spots appear on the new leaves, and the yellow spots gradually spread to the whole leaf; the plant is also easily infected by viral diseases.
With sulfur deficiency in tomato, the areas between the leaf veins turn yellow, the petioles and stems turn red, the internodes shorten, and the leaves become smaller. The overall plant color fades, appearing light green or yellow-green.
With iron deficiency in tomato, yellow-white discoloration first appears on the terminal buds and new leaves, with green remaining along the leaf veins, and the leaves become thinner; generally there is no browning or necrosis, and grayish yellow spots also appear at the base of the leaves.
Excessive nitrogen in tomato causes excessive vegetative growth, a low fruit-setting rate, reduced ability to resist pests and diseases, fruit that is not resistant to pressure and has a short fresh-keeping period. The fruit symptoms of excessive nitrogen are similar to those of potassium deficiency, and potassium fertilizer can be used to correct the symptoms of excessive nitrogen.
With manganese deficiency in tomato, the green between the veins of new leaves fades and turns yellow, while the veins remain green and the vein pattern is relatively clear; severe manganese deficiency produces grayish white or brown spots.
With boron deficiency in tomato, rust spots appear on the fruit surface; with boron deficiency in tomato, the terminal bud stops growing, the fruit skin and flesh become necrotic and corky, flowers form but no fruit sets, and rust spots easily appear on the fruit surface.
Tomato is sensitive to magnesium deficiency. With magnesium deficiency, chlorotic yellow spots appear between the veins of the lower leaves, the leaf margins turn various colors such as orange, red, and purple, and the fruit also fades from red to pale orange, with reduced stickiness of the flesh.
With molybdenum deficiency in tomato, during the true leaf stage the leaves turn yellow and curl, the new leaves are mottled, the chlorotic parts arch upward, the small leaflets curl upward, and finally the tips and margins of the small leaflets shrivel and die.