As we all know, crop plants require 17 nutrients to complete their life cycle.

Essential plant nutrients are divided into macro and micronutrient groups.

Macronutrients fall under into 2 sub components viz., primary & secondary macronutrients
Primary macronutrients include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P) & potassium (K), while secondary macronutrients include calcium (Ca), magnesium (Mg) and sulphur (S).

Micronutrients include zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), boron (B), molybdenum (Mo), chlorine (Cl), and nickel (Ni).

Further, the essentiality of silicon (Si), sodium (Na), vanadium (V), and cobalt (Co) has been considered, but is not yet proven.

Macronutrients are required in higher amounts compared to micronutrients.
However, from the plant essentiality point of view, all the nutrients are equally important for plant growth.

The first three macronutrients (C, H, and O) are supplied to plants by air and water. Hence, their supply to plants is not at all a problem.
The remaining 14 nutrients should be present in the plant growing medium in adequate amount and proportion for plant development and growth

When the supply of a particular nutrient is at an inadequate level in the soil or when plant roots are not able to absorb required amounts, due to unfavourable conditions in the rhizosphere, plants show certain growth disorders. These disorders may be stunted growth, discolouration of leaves, reduced root growth and also reduction in growth of newly emerging parts of the plant.

Visual symptoms are the cheapest nutritional disorders diagnostic technique that is most available.
However, it needs a lot of experience on the part of the observer, because deficiency symptoms are confused with drought, insects and disease infestation, herbicide damage, soil salinity and inadequate drainage problems. Sometimes, a plant may be on borderline with respect to deficiency and adequacy of a given nutrient. In this situation there are no visual symptoms, but the plant is not producing at its capacity. This condition is frequently called hidden hunger.

Guideline 1:

Deficiency symptoms normally occur over an area and not on an individual plant. If a symptom is found on a single plant, it may be due to disease or insect injury or a genetic variation.

Guideline 2:

Also, the earlier symptoms are often more useful than late mature symptoms.

Guideline 3:

Where the symptomology occurs on the plant depends on the mobility of the nutrient within the plant. Plant nutrients can be classified as mobile or immobile within the plant. Mobile nutrients such as N, P, K, Mg can be translocated from the older to the older leaves to the developing plant parts and hence, deficiency symptoms tend to show on older lower leaves. On the other hand, immobile nutrients (Many micronutrients, Ca, and S) are not easily translocated within the plants and deficiency symptoms occur in younger upper leaves.

Guideline 4:

The form and location of symptoms on the affected crop will help in guiding the diagnosis. Symptoms associated with deficiency may take several forms including chlorosis, necrosis, or abnormal growth. Chlorosis occurs when the production of chlorophyll is reduced which results in a yellow to pale green leaf colour. Nitrogen (N), sulphur (S), iron (Fe), and magnesium (Mg) are nutrients that play important roles in chlorophyll production and function, hence, their deficiencies tend to cause chlorosis. Next is necrosis, which occurs when the plant tissue dies. Necrosis is commonly associated with N, phosphorus (P), and potassium (K) deficiencies. Abnormal growth occurs when the inadequate amounts of a nutrient in the plant restrict cell elongation and replication resulting in stunted growth, deformation, or crinkled leaves.

With this basic information on hand, it is possible to pinpoint specific nutritional deficiencies in crop plants and frame needed management practices.

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