Wednesday, 15 October 2008

Mineral deficiences in plants

In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green colour of leaves, chlorotic leaves are pale, yellow, or yellow-white.

The affected plant has little or no ability to manufacture carbohydrates through photosynthesis and in extreme cases may die unless the cause of its chlorophyll insufficiency is treated. Specific nutrient deficiencies (often aggravated by high soil pH) produce chlorosis, which may be corrected by supplemental feedings of missing compounds in various combinations. Different mineral deficiencies act in subtly different ways.

Deficiency of Nitrogen (N)
The characteristic deficiency symptom of nitrogen is the appearance of uniform yellowing of leaves including the veins, this being more pronounced on older leaves. The leaves become stiff and erect. If the condition of nitrogen stress persists, then the result is decreased foliage and shoot growth.

Conditions inducing Nitrogen deficiency include heavy rain causing leeching, low organic matter content of soils, denitrifcation (losses of N2 and N2O to the atmosphere).

Deficiency of Magnesium (Mg)
Magnesium deficiency causes yellowing, but differs from that of nitrogen. The yellowing takes place in between veins of older leaves and veins remain green, this is followed by necrosis (unnatural death) of tissues. Interestingly, Mg deficiency may be induced in tomatoes by high levels of ammonium in the nutrient solution (Kafkafi et al., 1971).

Deficiency of Iron (Fe)
The principal veins remain conspicuously green and the surrounding portion of the younger leaves turn yellow.
Conditions inducing Iron deficiency include calcarous soils, soils high in P, Mn, Cu, or Zn, high rate of liming.

Deficiency of Potassium (K)
Under potassium stress condition, the yellowing of leaves starts from the tips or margins of leaves extending towards the center of leaf base. The yellowing is interveinal and these yellow parts become necrotic (dead spots) with leaf curling.

These are some of the more common causes of mineral deficiency, and as there are many more minerals making a contribution to the Cannas growth, then we can see that these are the first causes that should be investigated when chlorosis is spotted on foliage.

What is the best way to overcome these Environmental deficiences? Well, that is obviously to deliver the missing minerals to the chlorotic plant. The best immediate source of trace minerals is a liquid feed with seaweed fertilizer. However, that is only a temporary fix, as the basic soil deficiency has to be corrected by introducing the missing element(s).

And what happens if there is no improvement from the upgraded feeding regime? Then it is now time to think the worst and start considering the possibility of chlorosis induced by Canna virus, more of which later.

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