Growing Poplar and Willow Trees on Farms, National - FAO

yegrass-based pastures is reduced <strong>and</strong> livestock disorders like ryegrass
staggers <strong>and</strong> facial eczema often threaten herd health.
Irrigation would begin late in spring <strong>and</strong> continue until late autumn when
cows are dried off. The trees are irrigated with fresh effluent using a suitable
irrigator down the centre of each coppice block so that minimum effluent is
sprayed on the tree foliage. This avoids making the fodder unpalatable to
livestock. Irrigation frequency will depend on the runoff from the milking
shed <strong>and</strong> water may need to be used when the foliage becomes coated by
effluent. The trees may need a water wash after irrigating with effluent to
prevent the latter drying on the foliage. Using K-Line irrigation or installing
a border-dyke system may minimise this problem.
Tree growth in these blocks is rapid because of the high nutrient return, <strong>and</strong>
the irrigated trees soon form a closed canopy. One potential problem with
poplars could be rust infestation helped by the moist conditions (rainfall <strong>and</strong>
regular irrigation) during much of the growing season. These trees would
probably be harvested using machinery as a traditional coppice – to 15-20
cm above the soil surface, <strong>and</strong> the foliage fed to cattle, probably to dry stock
on-farm or off-farm. However cattle could still graze them, preferably using
dry stock.
<strong>Willow</strong> is more suitable for use in this system, because of its longer growing
season <strong>and</strong> a higher foliage-to-wood ratio <strong>and</strong> nutrient uptake than poplar.
However, using willow <strong>and</strong> poplar in coppice blocks for effluent
management on dairy farms will depend on long-term growth rates. When
their growth rates are high, more effluent could be applied to a coppice
block than to pasture without increasing leaching. This would reduce the
l<strong>and</strong> area required for irrigating effluent – an advantage on farms where soil
type or topography restricts the area suitable for irrigation.
Nutrient uptake should match the nutrient quantities applied to prevent any
leaching into waterways. These trees are deeper rooting than pasture plants,
so they could be valuable during wet weather where storing effluent is not
practicable or where there are heightened concerns about the effects of
nitrate leaching, such as in the Lake Taupo catchment. Coppice blocks can
be used in conjunction with on-farm effluent storage facilities.
The Otago trial is using the K-Line irrigation system with great success, as
this accurately applies up to 5 mm of liquid effluent per hour. In the trial the
irrigator lines were about 15 m apart running in parallel lines to one another.
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