Diagnosing Nutrient Deficiency Symptoms in Crop Plants
A mineral element is considered as essential when plants cannot complete their reproductive stage of life cycle due to its deficiency. Based on these criteria, seventeen elements so far were identified as essential. These are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl) and nickel (Ni). Among these, carbon, hydrogen and oxygen are taken up from air and water. The rest of the elements are taken up from the soil solution as mineral nutrients. Among these nutrients N, P, K, Ca, Mg, and S are considered major or macro-nutrients, because they are required in large quantities that range between 1 to 150 g per kg of plant dry matter. Fe, Zn, Mn, Cu, B, Mo, Cl and Ni are minor or micro-nutrients that are required at rates of 0.1 to 100 mg per kg of plant dry matter. All the essential nutrients are required by plants in balanced proportions for optimum growth.
Nutrient deficiency occurs when an essential element is not available in sufficient quantity to meet the requirements of a growing plant. These nutrient deficiencies are often manifested as visual symptoms on plant parts that help recognize specific nutrient deficiencies. Early detection of a nutritional disorder by recognizing these symptoms can help to prevent major loss of yield by application of the required nutrient through fertilizer sources.
Recognizing nutrient deficiency in crop plants is often difficult as some of them could look similar even to experienced eyes. For instance, nitrogen (N) and sulfur (S) deficiency symptoms can be very similar, depending upon placement, growth stage, and severity of deficiencies. Multiple deficiencies can occur at the same time which could be very confusing at first look. Pseudo deficiency symptoms (visual symptoms appearing similar to nutrient deficiency symptoms) caused by disease, drought, excess water, genetic abnormalities, herbicide and pesticide residues, insects, and soil compaction can cause false identification of deficiency symptoms. Besides, symptoms in actual field situations may appear different than ‘ideal’ symptoms. However, understanding the basics of nutrient deficiency and field experience could make identification easier.
A first step in diagnosing nutrient deficiencies is to describe what the symptoms look like. Each deficiency symptom is related to some function of the nutrient in the plant. Symptoms caused by nutrient deficiencies are generally grouped into five categories: 1) stunted growth; 2) chlorosis; 3) interveinal chlorosis; 4) purplish-red coloring; and 5) necrosis.
Stunting is a common symptom for many deficient nutrients due to their varied roles in
the plant. For example, when nutrients involved in plant functions such as stem elongation, photosynthesis, and protein production are deficient, plant growth is typically slow and plants are small in stature. Chlorosis and interveinal chlorosis are found in plants deficient of nutrients necessary for photosynthesis and/or chlorophyll production. Chlorosis can result in either the entire plant or leaf turning light green to yellow, or appear more localized as white or yellow spotting. Interveinal chlorosis is the yellowing of leaf tissue between veins, with the veins themselves remaining green. Purplish-red discolorations in plant stems and leaves are due to above normal levels of anthocyanin that can accumulate when plant functions are disrupted or stressed. This symptom can be particularly difficult to diagnose because cool temperatures, disease, drought, and even maturation of some plants can also cause anthocyanin to accumulate. Certain plant cultivars may also exhibit this purple coloring. Necrosis generally happens in later stages of a deficiency and causes the parts of the plant first affected by the deficiency to brown and die. Since a number of nutrient deficiencies can produce similar symptoms, further evaluation of symptoms related to particular leaf patterns or locations on the plant will be needed to diagnose nutrient specific deficiencies.
Another step in identifying deficiency symptoms is to determine whether the deficiency is the result of a mobile or immobile nutrient based on where the symptom is appearing in the whole plant. Mobile nutrients are nutrients that are able to move out of
older leaves to younger plant parts when supplies are inadequate. Mobile nutrients
include N, P, K, Cl, Mg, and Mo. Because these nutrients are mobile, visual deficiencies will first occur in the older or lower leaves and effects can be either localized or generalized. In contrast, immobile nutrients (B, Ca, Cu, Fe, Mn, Ni, S, and Zn) are not able to move from one plant part to another quickly and deficiency symptoms will initially occur in the younger or upper leaves and be localized. Zn is a partial exception to this as it is only somewhat immobile in the plant, causing Zn deficiency symptoms to initially appear on middle leaves and then affect both older and younger leaves as the deficiency develops.
The following flowchart provides the key to recognize nutrient deficiency symptoms in plants with actual field photos as examples. However, it must be clearly recognized that considerable amount of yield is already lost by the time nutrient deficiencies become apparent in the plants. So to maximize yield and profit soil test and yield target-based application of nutrients is essential.
Source: Modified from Nutrient Management Module 9 (2003). Plant Nutrient Functions and Deficiency and Toxicity Symptoms by Ann McCauley, Clain Jones and Jeff Jacobsen. Montana State University Extension Service.
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