Plant Mineral Deficiencies
Plant Mineral Deficiencies
A plant that is short of food may grow poorly and exhibit a range of symptoms on leaves, stems and fruit including discoloration and growth distortion. This condition is known as a mineral or nutrient deficiency and can be caused by a number of factors.
A shortage in the
A mineral deficiency can develop as a result of a shortage of a particular nutrient in the soil. This can be rectified simply by applying the missing mineral to the plant or the soil. Where appropriate, the soil structure should be improved in order to help it retain the added nutrients.
Sources of plant foods to correct various mineral deficiencies are given under each specific deficiency described below. Short-term materials should have an effect in the season in which the deficiency is noticed. While they will improve new growth, they will not cure existing symptoms. The soil should then be improved by using the longer-term materials and cultural practices.
Deficiencies can also develop on soils that are not short of plant foods but where something is making the nutrients unavailable to plants. In this case, correct the particular adverse condition (or simply wait for it to pass).
Causes of induced deficiencies
The following are all causes of induced deficiencies:
• Heavy soils are usually rich in plant foods, but if the soil structure is poor andimpeded, then these plant foods will unfortunately not be available to the growing plant.
• A sudden period of cold weather, checking plant growth and activity of soil life, can cause a temporary deficiency in both. This will hopefully disappear when the temperature rises again.
• Shortage of water in the soil can reduce nutrient uptake.
• Adding uncomposted tough material to the soil can reduce the available nitrogen supplies temporarily. This is commonly known as nitrogen depletion.
• Excessive or insufficient liming or fertilizer application can make certain nutrients unavailable to plants. This can also be the case if the soil is too acid. It is important to identify a deficiency and its cause correctly rather than adding extra food “just in case”.
• Root damage, whether by pest, disease or waterlogging may make a plant unable to take up the food it requires.
Mineral deficiencies are not easy to diagnose; the symptoms may be confused with those caused by viruses, disorders or other factors. If a problem occurs regularly and diagnosis is unsure, a commercial soil analysis may be needed to establish the cause.
The most likely cause is over-liming, making boron unavailable to plants; high nitrogen use can exacerbate the problem. Symptoms are typically distortion and blackening of leaves, together with cracked and/or corky areas on stems and midribs.
Short term — rake in borax at 3g per sq m.
Cultural — correct soil conditions.
Calcium deficiency is usually the result of disruption in the supply of calcium to the plant rather than a soil deficiency. It can be caused by a shortage of water, which slows the transport of calcium, or by excessive use of potassium or magnesium fertilizers. Two common conditions caused by this deficiency are blossom end rot inand bitter pit in apples.
Short term — none.
Longer term — limestone and gypsum will supply calcium if soil is deficient.
Cultural — maintain conditions that allow steady, uniform growth throughout the season. A steady water supply is essential.
This deficiency is almost always a result of a naturally high soil pH (over 7.5), which reduces the availability of this element to plants. The symptoms of deficient plants include yellow between the leaf veins, or all over, giving a very bleached look. Perennial crops are much more susceptible to this deficiency; annuals seldom show symptoms.
Iron deficiency is sometimes confused with manganese deficiency, but it is completely different.
Short term — chelated (sequestered) iron. Cultural — do not grow acid-loving plants on alkaline soil. Improve soil structure.
One of the more common deficiencies, especially on sandy soils and in wet weather. Soil compaction, waterlogging and water stress all aggravate the condition. Excess application of potassium fertilizers can make magnesium unavailable to plants. The typical symptom is yellowing between the leaf veins, on the older leaves first, giving a mottled appearance. Symptoms may be confused with virus or natural ageing.
Short term — foliar feed every two weeks with a 2 per cent solution of 10 per cent Epsom salts.
Longer term — reduce use of potassium fertilizers if appropriate; add dolomite limestone if pH allows.
Most likely to occur on soils with a high pH (over 7.5) and/or poor drainage and/ or high organic matter levels. The typical symptom is yellowing between the leaf veins on the youngest leaves first. Manganese deficiency can often be confused with both iron or magnesium deficiency.
Short term — spray deficient plants with manganese sulphate dissolved in water at 50g (2 oz) in 11.5 litre (21/2 gal) water, two or three times at two-week intervals.
Cultural — always check pH before liming.
Only likely on poor and neglected soils low in organic matter or in pot-bound plants. A nitrogen deficiency can be induced by nitrogen robbery. Typical symptoms, which appear on the oldest leaves first, are poor, spindly growth and pale yellow leaves; these may turn reddish-purple. Similar symptoms may also be caused by root damage and phosphorus deficiency.
Prevention and treatment
Short term — liquid feeds; grass mowings.
Longer term—animal manures; compost; blood,and bone meal; hoof and horn.
Cultural — grow legumes;; improve soil organic matter levels.
Most common in areas of high rainfall, especially on acid soils and during cold spells. Symptoms include poor growth, especially in young plants. Leaves may also develop a dull blue tinge.
Short term — none.
Longer term — bone meal; bone flour; rock phosphate.
Cultural — lime soil to raise pH if appropriate.
Most likely on light, sandy, peaty, or chalky soils. Plants that require a lot of potash, such as, beans and fruit, may show deficiencies on more fertile soils. Typical symptoms, which appear on older leaves first, are scorching round the edge of leaves, which may curl up or down.
Short term — comfrey liquid manure; comfrey leaves; wood ash.
Longer term — seaweed meal; garden potash.
Cultural — improve soil structure.