Growing Poplar and Willow Trees on Farms, National - FAO

systems; either as vegetation to be directly irrigated by the effluent, or as
riparian buffer zone plantings to capture nitrogen from seepage or reirrigated
tile drainage.
The coppiced material must be cut <strong>and</strong> carried to stock, either milking or
dried-off cows, or other livestock to disperse the nutrient.
If used for effluent
nutrient uptake, blocks
should be located on l<strong>and</strong>
accessible to the effluent
irrigation system.
Flat l<strong>and</strong> is preferable but
gentle slopes up to 5-10
degrees may also be
suitable. After early
spring, soil moisture levels
are usually depleted by
sun <strong>and</strong> wind, <strong>and</strong> so
effluent runoff into drains
becomes less of a concern.
Coppiced willows
There is also more active growth of pastures at this time, which assimilates
more nutrients.
The effluent returned on these coppice blocks will raise soil nutrient levels.
In theory, the trees ought to absorb the applied nutrients at the same rate as
they are distributed on the area, to prevent leaching into groundwater <strong>and</strong>
run-off into streams. In practice this nutrient balance can be difficult to
determine due to variations in soil type, pasture cover <strong>and</strong> the local climatic
conditions.
For example, annual rates of up to 400 kg of nitrogen/ha were recorded
being uplifted by a ‘Tangoio’ willow coppice block in a trial at Carterton,
Wairarapa.
The procedure for planting effluent coppice blocks is the same as described
for browse blocks though high planting rates of 12,000-15,000 stems/ha are
recommended, to increase nutrient uptake <strong>and</strong> reduce competition from
pasture. The plant material used will also be similar, as will methods used to
plant them – although access should be much easier on these sites.
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