Geoscience Reference
In-Depth Information
The micro, or trace, nutrients, are all required in very small amounts, but are
essential for healthy plant growth. The availability of these nutrients is often
dependent on soil pH, and in strongly acid or alkaline conditions they may be
either unavailable to plants or available at toxic levels. (Refer to Chapter 9.)
Keeping soil at near neutral or slightly acid pH overcomes many problems with
trace elements, but if deficiency signs occur in crops, or if a known deficiency is
present, the required trace element should be added.
Antagonism between nutrients
When talking of nutrient deficiencies or excesses we are talking about fine tuning
the balance of each plant food in the soil. Too much of a nutrient may be even
worse than too little for the reason that it may be hard to remove excesses (e.g.
sodium or manganese). Some of the plant nutrients in excess can cause other
deficiencies in plants by interfering with the uptake of a nutrient that would
normally be in adequate supply. Overdosing with one plant nutrient may change
the availability of others. Table 2 shows some examples.
Just as it is possible to have too little of a nutrient in the soil, it is also
possible to have too much.
Table 2
Some soil nutrient interrelationships in plants
Nutrient in excess
Induced deficiency
Nitrogen
Potassium
Magnesium
Potassium, nitrogen, phosphorus. Calcium shows as
magnesium deficiency
Potassium
Magnesium, sodium, calcium
Sodium
Calcium, potassium
Calcium
Phosphorus, magnesium, trace elements
Boron
Potassium, magnesium
Chlorine
Potassium
As well as soil nutrients affecting plant health, nutrients supplied to animals
from plants grown on the soil also affect animal health, as shown in Figures 7 and
8. If an arrow points from one nutrient to another, it means a deficiency in the
nutrient the arrow is pointing to may be caused by excess of the first nutrient. A
nutrient in excess can affect more than one other nutrient.
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