Silviculture / Modification of the physical environment / Fertilisation
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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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