Everything you wanted to know about fertilization and plant nutrition!
Visual identification of nutrient deficiency symptoms can be a practical tool for evaluating the nutrient status of the plant In addition to soil and tissue analysis.
In order to correctly identify the nutrient deficiency, one should be familiar with the factors affecting their development.
Symptoms such as tip burns, chlorosis or necrosis, which are characteristic to some nutrient deficiencies, can also be associated with other stresses. Here are some examples:
Plant disease - some plant disease symptoms might be misinterpreted as nutrient deficiencies. Plant disease and nutrient deficiencies can be differentiated by the distribution of the symptoms throughout the crop.
If symptoms do not occur uniformly across the affected plants, but vary between plants, it is more likely that they are related to plant disease rather than to nutrient deficiencies.
Chemical spray/chemigation - under certain circumstances, chemicals applied to the plants might induce symptoms which can resemble to nutrient deficiencies. Knowing the spray history can help you in determining whether symptoms on the plants are related to the spray.
You should also pay attention to the timing when symptoms occur. If symptoms occur soon after a chemical was applied, they might be related to the chemical.
The distribution of the symptoms can give you another clue. In most cases, spraying does not cover the plants uniformly. Note the path of spraying and compare it to it to the occurrence of the symptoms.
Salinity stress - salinity damages, such as tip burns might be misinterpreted as nutrient deficiencies. For example marginal leaf burns might be interpreted as potassium deficiency.
The location on the plant where deficiency symptoms are expressed can help in diagnosing the nutrient disorder.
Plant nutrients can be divided to two groups - mobile nutrients and immobile nutrients. Mobile nutrients can be translocated from older leaves to younger ones, while immobile nutrients cannot.
The mobility of a nutrient in the plant affects the location of the deficiency symptom on the plant.
Deficiency symptoms of mobile nutrients will first develop on the older mature leaves. Basically, nutrients are translocated by the plant to its actively growing parts, which are the younger leaves.
Deficiency symptoms of immobile nutrients will first show up in the newer growth because these nutrients cannot be translocated from the older leaves to the new growth.
|Very mobile nutrients||Moderately mobile nutrients||Immobile nutrients|
Sulfur (mobility varies with species)
The first question you should ask yourself when attempting to identify the nutrient deficiency, is whether the reason for the deficiency is a shortage of the nutrient in the soil/water, or are there other factors that induce the deficiency.
In many cases, it may be more efficient correcting the cause for the deficiency rather than trying to correct the deficiency itself by augmenting the nutrient in deficiency.
Over-watering affects the availability of nutrients to the plant. It results in lack of oxygen and a poor root system. The efficiency of nutrient uptake is reduced and nutrient deficiencies, such as iron deficiency, might be induced. In addition, over-watering leaches nutrients from the root zone.
Under-watering may also affect nutrient availability to the plant. When the soil is dry, the movement of water through the soil is reduced. Since nutrients move in soil together with water, their availability to the plant is reduced as well.
Nutrient Antagonism and Competition
Often, nutrient deficiency symptoms are a result of interactions between the nutrients. An excess of one nutrient can cause a deficiency of another. This is because some nutrients have similar uptake mechanisms.
For example, excess of potassium can interfere with the uptake of magnesium and excess of metals such as manganese or zinc can induce iron deficiencies. This kind of interactions is referred to as "nutrient antagonism".
The pH plays an important role in the availability of nutrients. The pH affects most reactions with soil particles and other nutrients. Most affected by pH are the micronutrients, but the uptake of nutrients such as calcium and magnesium is also affected (it is reduced in low pH).
Nutrient deficiencies are induced when pH is higher or lower than the recommended pH range for individual plants. Fixation of nutrients is influenced by soil pH. Fixation refers to the reactions of soil particles with nutrients, which render them unavailable to plants.
Magnesium deficiency resulted from low pH
There are many factors that might affect the nutrition status of your crop; some of them are described in this article.
Some symptoms, which are not nutrient deficiency symptoms, might be misinterpreted as nutrient deficiency symptoms.
In many cases it is more practical to treat the cause of the nutrient deficiency, rather than add the deficient nutrient.
A visual identification of nutrient deficiencies can be used as a practical and quick diagnostic tool. Nevertheless, it has a major drawback: Once deficiency symptoms occur, there is already a major effect on yield, growth and development.
Article by Guy Sela, international expert in plant nutrition and irrigation.