The Effect of Soil pH on Trace Elements
In many cases the deficiency or toxicity of trace elements can be cured by altering the
pH of the soil. For example Molybdenum can usually be made available to plants if lime
is added to an acid soil, though in many tropical soils no Molybdenum at all is present.
In this case Molybdenum must be added to the soil, for at least five years or even ten, in
addition to lime.
Trace Elements in Context
Plants need three different types of nutrients in order to grow well:
- Major Nutrients, also known as macronutrients or primary nutrients, these are:
- Secondary (Minor) Nutrients, which are also essential for healthy plant growth but
in much smaller quantities: Calcium (Ca), Magnesium (Mg) and Sulphur (S). - Trace Elements, which are also essential for healthy plant growth but only in very
small quantities.
A Warning about Symptoms of Plant Nutrient Deficiencies or Toxicities
The symptoms of nutrient deficiency or toxicity that are displayed by plants are
described in the following paragraph. Deficiencies may in fact be sub-clinical, where the
The Role of Plant Nutrients
An explanation of the following: each element, or “nutrient”, is described in four ways:
in terms of its function in plant growth (“Function”), the plant species which are most
affected by the nutrient (“Indicator Plants”), the “Symptoms” shown by plants when
they are grown in soils which are either deficient (D) or have excessive amounts (E) of
that nutrient, and some “Remarks”.
Nitrogen (N)
Function: to increase plant growth, the size of the leaves and yield.
Indicator plants: cereals, mustard, apples, citrus.
Symptoms: Leaves are chlorotic (yellow or pale green). Older leaves are yellow at the
tips. Leaf margins green, but midribs yellow. Plants are stunted (D).
Remarks: Nitrogen may give dramatic and quick response by plants, but too much N
causes too much vegetative growth with weak stems, sometimes causing lodging, and
also increases the susceptibility of plants to disease, frost and drought.
Phosphorus (P)
Function: to develop root growth, to establish young plants and to help early ripening.
Indicator plants: legumes, root crops, maize, barley, lettuce and tomatoes.
damage, poorly applied fertiliser.
tion known as transient deficiency: cold weather, drought, saline soil, mechanical
plants when they are subjected to one or more of the following conditions, a situa-
To complicate matters further, these same symptoms may also be shown bycrop does not manifest physical symptoms, but its performance is adversely affected.
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Nitrogen (N), Phosphorus (P) and Potassium (K).