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Fertilisation
It is common practice in many forestry operations to add fertilisers
when trees are planted or soon after. Achieving a growth response
to fertilisation depends on two factors:
• whether nutrients were limiting growth before fertilisation;
• whether or not there is sufficient moisture to make the
nutrients available to the plant.
There is often little or no long-term response to fertiliser
applications on farm soils. Weeds must be totally eliminated
from around young trees at the time of fertilisation. If there
are weeds around young trees when the fertiliser is applied,
it could encourage their growth and increase competition for
moisture, resulting in poorer tree growth. It is important to
apply fertiliser, especially nitrogen, at the right time because
it can be leached away before the plants are advanced enough
to use it.
Nitrogen, phosphorous, sulphur and potassium are all important
nutrients for tree growth and development. Symptoms of nutrient
deficiencies, although often specific to particular species,
can provide a guide to what is required. Trace elements of importance
to tree growth that are often implicated in causing disease
or poor development include copper and boron. Foliar sampling
is becoming standard practice in industrial forestry. It might
be useful for pre-empting problems and targeting fertiliser
applications more effectively. Soil sampling to detect deficiencies
is thought to be less effective for trees than for pasture and
crops. Trees are able to access nutrients from deeper in the
soil and may be able to access nutrients unavailable to annual
crops.
As local knowledge of nutrient deficiencies and plant responses
is generated and shared, growers will be able to more effectively
determine their own fertiliser needs. Until then growers might
decide to undertake small-scale fertiliser trials on their own
properties or make general applications of broad based fertilisers
as a precautionary measure. It might be worth taking samples
for analysis when the foliage shows signs of nutrient deficiency—for
example, where there is yellowing, spotting, discoloration or
malformed growth of the leading stems.
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