Nitrogen deficiency symptom: Chlorosis of older leaves. Photos: Dr Nor Elliza Tajidin
When plants suffer from a deficiency in one or more nutrients, they display specific signs. While it is relatively straightforward to diagnose these signs, the task can become complicated due to the overlap between symptoms of nutrient deficiencies, or abiotic issues, and those of plant diseases or pest infestations, or biotic issues.
A useful method for differentiating between abiotic and biotic issues is to observe the uniformity of symptom distribution in a given area.
Biotic problems, like diseases and pest infestations, usually appear patchy, affecting some plants while leaving others unscathed, even those in close proximity. However, over time, these biotic problems can spread and affect all plants.
In contrast, nutrient deficiencies typically manifest more uniformly across an area, with all plants displaying the same signs, as opposed to a sporadic appearance on individual plants.
Nutrient deficiencies in plants generally materialise in six distinct ways: stunted growth, leaf yellowing or chlorosis, interveinal chlorosis, purplish-red discoloration, tissue death or necrosis (appearing like burn marks), and deformities in plant parts (such as leaves, roots, and flowers).
Phosphorus deficiency in corn will cause older leaves to display purplish red leaf margins.
Diagnosing plant nutrient deficiencies becomes easier if we understand nutrient mobility. Mobile nutrients like nitrogen, phosphorus, potassium, and magnesium are so-called because these nutrients can be reallocated within the plant, moving from older to younger tissues to support growth when these nutrients are lacking.
Consequently, deficiencies in mobile nutrients manifest first in older leaves, gradually progressing to younger leaves.
Conversely, immobile nutrients, such as calcium, iron, manganese, boron, copper, and zinc, cannot be reallocated once utilised in a specific part of the plant. Therefore, deficiencies in these nutrients manifest first on new growth or younger leaves, as they cannot be transported from older leaves.
A third category includes partially mobile nutrients like sulfur and molybdenum, which can be relocated within the plant but with lesser mobility than mobile nutrients.
Leaf margin necrosis indicating potassium deficiency.
To recap: if symptoms appear only on older leaves, the plant is likely deficient in mobile nutrients; if they appear only on younger leaves, it suggests an immobile nutrient deficiency; or if symptoms appear throughout the plant, a partially mobile nutrient is likely deficient.
Once we have determined the category of nutrient deficiency our plants are facing, we can further identify the exact nutrient in deficit.
For instance, magnesium deficiency is characterised by the leaf areas between veins turning chlorotic, while whole leaf chlorosis suggests nitrogen or phosphorus deficiencies.
Potassium deficiency is discernible by necrotic leaf margins and tips. Similarly, nitrogen deficiency often leads to whole leaf chlorosis, premature leaf shedding, and early flowering. Phosphorus deficiency presents similarly but with purplish red leaf margins and unbranched, elongated roots.
Magnesium-deficient pak choy leaves display interveinal chlorosis of older leaves.
Sulfur and molybdenum deficiencies result in leaf chlorosis over the entire canopy, potentially leading to pale flowers and stems.
Deformed young leaves often indicate calcium deficiency, while boron deficiency is associated with aborted young shoots and excessive branching. Both these deficiencies typically appear at the growing points of the plant.
Iron, manganese, copper, and zinc deficiencies are less common in acidic soils, such as those in Malaysia.
Regular visual monitoring aids early detection of nutrient deficiencies, allowing for proactive and remedial measures to maintain plant health and productivity.
Dr Nor Elliza Tajidin is a senior lecturer at the Department of Crop Science, Faculty of Agriculture, Universiti Putra Malaysia.
