Plants need at least seventeen essential nutrients to complete their life cycles. Scientists group these essential nutrients into macronutrients (carbon, hydrogen, oxygen, nitrogen, potassium, phosphorus, sulfur, calcium and magnesium), which are required in large quantities and micronutrients (zinc, iron, copper, boron, manganese, chlorine, molybdenum and nickel), which are required in small quantities. Sufficient amounts of these nutrients are required in order for plants to produce well. If there is a deficiency of any essential element, yield and quality can be reduced. Also, too much a nutrient can be toxic to plants. Diagnosing nutrient deficiencies and toxicities are important for growers and gardeners to ensure optimum yield and quality.

When low on an essential nutrient, plants exhibit distinct visual symptoms that allows us to distinguish which nutrient is deficient. A first step in diagnosing nutrient deficiencies is to describe what the symptoms look like. Symptoms caused by nutrient deficiencies are generally grouped into five categories: 1) stunted growth; 2) chlorosis or yellowing; 3) leaf spots; 4) purplish-red coloring; and 5) necrosis (death of tissue). The next step is to identify whether the deficiency symptoms appear on older (lower) leaves or younger (upper) leaves first. If the deficiency symptoms appear on older leaves first, then the deficiency symptoms are possibly caused by one of the nutrients that are mobile in plants, such as nitrogen, phosphorus, potassium, magnesium, chlorine, or molybdenum. In contrast, deficiency of nutrients that are immobile (calcium, sulfur, boron, copper, iron, zinc, manganese, nickel), the symptoms first appear on younger or upper leaves.

Nitrogen deficiency symptoms are chlorosis of lower leaves (light green to yellow), stunted and slow growth and, in severe cases, necrosis of older leaves. Nitrogen deficient plants will mature early and crop quality and yield are often reduced. In cereal crops, chlorosis appears as an inverted “V” down the midrib. Insufficient amounts of N in cereals also result in fewer tillers, slender and weak stalks, short heads, and low grain protein content. Leaf curling and small tubers are common in potatoes deficient of N.

Chlorosis appearing as an inverted ‘V’. Photo contributed by H. Tao
Nitrogen deficiency results in slender and weak stalks in cereal crops. Photo contributed by H. Tao.
Canola plants show general chlorosis pattern in older leaves. Photo contributed by H. Tao.

Phosphorus deficiency symptoms occur in the older leaves first and typical deficiency symptoms are purpling of leaves and leaf margins and stunted growth. Plants that are deficient in phosphorus are generally weak and maturity is delayed. When phosphorus deficient, small grains tend to be stressed and predisposed to root rot diseases. Potato phosphorus deficiency symptoms include leaves curling upward and tubers having brown internal specks, often radiating out from the core.

Phosphorus deficiency in corn. Note the purplish color of the leaves. Photo contributed by H. Tao.
Canola leaves exhibit purple coloration due to phosphorus deficiency. Photo contributed by H. Tao.

Potassium deficiency symptoms first appear on older leaves. Typical deficiency symptoms are yellowing and necrosis of the leaf margins. When potassium deficiency is severe, older leaves turn yellow with tissue necrosis along the margins, but the upper new leaves may stay green. Potassium-deficient plants tend to lodge late in the growing season. Sometimes one may confuse potassium and nitrogen deficiency because both show typical chlorosis that appear on older (lower) leaves first. The difference is the chlorosis starts from the tip and progress along the ribs of the leaf if nitrogen is deficient and the chlorosis start from the tip and progress along the edge of the leaf if potassium is deficient.

Chlorosis due to nitrogen deficiency starts at the tip and progresses along the ribs. Photo contributed by H. Tao.
Chlorosis due to potassium deficiency starts at the tip and progresses along the leaf edges. Photo contributed by H. Tao.

Another nutrient that is commonly found deficient is calcium. Typical calcium deficiency symptoms are poor leaf expansion, curling followed by necrotic patches in the young leaves. Calcium deficiency can cause misshapen fruit and aborted buds. If you find the tip of tomatoes or peppers rotting, cavity spots in carrots or black heart in peanuts and celery, it’s likely the plants are calcium deficient. However, don’t hurry apply calcium fertilizers. Check on other stresses such as drought because lack of moisture in the soil can lead to insufficient uptake and transportation of calcium within plants, which leads to symptoms similar to calcium deficiency appearing.

Calcium deficiency may cause leaf curling and dead patches. Photo contributed by H. Tao.
Blossom end rot in tomatoes. Photo by D. Pettinelli

In sandy and low organic matter soils, sulfur deficiency can occur. Typical sulfur deficiency symptoms are reduced plant growth rate as well as stunted and thin stemmed plants. In cruciferous crops (such as cabbage, broccoli, canola, rapeseeds, etc.), light green to yellow discoloration appears in younger leaves first. Undersides of leaves of cole crops (cabbage, broccoli, cauliflower, etc.) may take on a reddish color and leaves may be cupped inward.

Thinned stemmed and stunted plants may suggest a sulfur deficiency. Photo contributed by H. Tao
Sulfur deficient cole crops may exhibit a reddish color and cupped leaves. Photo contributed by H. Tao.

Precautions in identifying nutrient deficiency by visual clues alone include: (1) Many symptoms appear similar. For instance, nitrogen and sulfur deficiency symptoms can look very much alike especially when plants are young, and the deficiency is severe. (2) Multiple deficiencies and toxicities may occur at the same time. More than one deficiency or toxicity can produce symptoms, or possibly an excess of one nutrient can induce a deficiency of another. For example, excessive phosphorus fertilizer application can cause zinc deficiency and vice versa. (3) Some crop varieties are naturally light in color. (4) Other stresses such as disease, drought, excess water, genetic abnormalities, herbicide and pesticide residues injury, insects, and salt injury can also cause symptoms that may be similar to a nutrient deficiency. For instance, plants may exhibit phosphorus deficiency symptoms (reddish leaf color) in early spring even if your soil test is above optimum level. Fertilization is unnecessary because the symptoms will disappear as the weather gets warmer and plants get bigger. Salt injury can cause brown leaf margins that resemble a molybdenum deficiency. However, salt injury symptoms normally appear suddenly as a result of too much fertilizer and show up on all the leaves. (5) Plants may be nutrient deficient without showing visual symptoms. Experience and knowledge of field and management practices are necessary to aid the diagnostics. The best way to confirm if you have nutrient deficiency is to test your soil and plant tissue. Another way to verify if your crop is deficient of a nutrient is to apply this nutrient in a small area. If the deficiency symptoms disappear, it is likely that your crop is deficient of this nutrient. For questions on nutrient management in the garden or on farms, feel free to contact the UConn Soil Nutrient Analysis Lab at (860) 486-4274.

By Haiying Tao, PhD, Assistant Professor, UConn Plant Science LA