It’s relatively easy to check for disease and insect damage and inadequate soil moisture but nutrient deficiencies can be more difficult to diagnose.
Robert L. Mikkelsen, western director of the International Plant Nutrition Institute, says a quick review of terminology will help farmers know what to look for and how to describe what they find to plant pathologists or disease lab staff:
- Chlorosis – This condition indicates a yellowing of the leaf tissue. Because many nutrients are involved in chlorophyll formation and photosynthesis, many nutrient deficiencies can cause chlorosis symptoms.
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Chlorosis of the older leaves may be caused by a shortage of mobile nutrients such as nitrogen, potassium and magnesium. Chlorosis of the younger leaves may indicate a deficiency of an immobile nutrient such as sulfur or iron.
- Interveinal chlorosis – This occurs when the leaf tissue turns yellow while the vein itself remains green. In grass this is commonly called striping. Many of the micronutrient deficiencies show this symptom.
- Firing – Leaf yellowing may be followed by the rapid death of the tissue as symptoms move up the plant. The dead leaf tissue is described as scorched or fired.
- Necrosis – Severe nutrient deficiency will result in the death of plant parts or perhaps the entire plant. The dead tissue that remains on a still living plant is called necrotic tissue.
- Abnormal colour – Lack of adequate nutrition will cause plant leaves to produce abnormal colour compounds, which will vary between plant species. Some plants do not show distinct symptoms.
Red and purple colours are typical with phosphorus and magnesium deficiency.
Sometimes the plant will be totally bleached of colour, which can occur with iron deficiency.
- Stunting – A lack of any essential nutrients will result in decreased growth and yield. This depressed growth may shorten the height of many crops and result in smaller harvests.
Stunting is a general term that compares the decreased growth with plants that are not limited by poor nutrition.
Lack of adequate phosphorus frequently has no visual symptoms other than overall stunting.
While visible plant symptoms can be a useful guide for checking crops, plant growth is already impaired by the time they are noticeable and yield is lost each day the deficiency continues.
