The ideal riparian zone has a mixture of rank grass, native
plants and exotic trees, DairyNZ freshwater ecologist
Justin Kitto says. Photo from Allied Press files.
Trees could help solve farmers' concerns with nutrient
The Trees on Farms workshop at Pleasant Point on April 30
outlined the uses of trees to improve the environment.
AgFirst consultant Nicola Chisholm said there had been a lot
of investigation into trees' role in nutrient management.
Riparian strips had been shown to stabilise stream banks,
intercept groundwater, reduce nutrient input into streams and
help control stream temperatures.
However, they had only a minimal impact on reducing nitrogen
losses. Farm forestry blocks could reduce a farm's overall
nitrogen losses by balancing the nutrient equation.
Trees took up effluent, cleaned up waterways, helped with
drainage and helped to form litter layers to dam surface
runoff. They could be useful at ''leaky'' sites, Ms Chisholm
Dairy farm effluent could be used to irrigate growing trees.
A southern Wairarapa trial showed good uptake of nutrients in
some cases, she said. That research had potential
applications for poorly draining dairy farms.
Willows could be an option, because of their vigorous nature.
In an Otago trial, they took up a lot of effluent as long as
the application level was correct.
In Southland, willows had been successfully used to absorb
effluent at truck wash sites.
A farm had a gully planted in willows to take up effluent
running off a sloping paddock, Ms Chisholm said.
With climate change predicted to increase temperatures and
droughts on the South Island's east coast, landowners should
consider the role of trees, she said.
They would become more important as shade, because dairy cows
had lower milk yield and quality in hot conditions. Cows with
high genetic merit were the most susceptible to heat stress.
Lincoln University studies showed shelter removed the effects
of heat stress.
And while people suspected cows offered shade would sit in it
rather than grazing, the research revealed provision of shade
actually increased grazing time, Ms Chisholm said. The cows
also had a better feed conversion efficiency.
''Animals with shade do better.''
Shade and shelter trees could also produce fruit and nuts to
supplement a farm's income. Examples already working included
feijoas and chestnuts on a Waikato dairy farm and avocados in
An organic dairy farm in Britain was trialling willows that
cows would graze before the trees were harvested for
DairyNZ freshwater ecologist Justin Kitto said about 80% of
farm runoff came from about 20% of land - areas that leaked
only during high rainfall. Grass filter strips were
''fantastic'' at reducing sediment, phosphorus and bacteria,
Riparian planting could shade the waterway to prevent growth
of unwanted duckweed, improve the reproductive habitat for
invertebrates, and hold banks together to prevent sediment
entering the water.
The ideal riparian zone had a mixture of rank grass, native
plants and exotic trees, where appropriate, Mr Kitto said.
However, the whole river catchment needed to be planted or
managed. He had seen ''loads of cases'' where the efforts of
some farmers were undone by a person at the top of the
catchment letting contaminants pour in.
Planting was not the whole solution, either - nutrient inputs
and irrigation also had to be managed.
Meanwhile, the riparian zone was ''the picture postcard for
your farm and the state of New Zealand farms in the public's
eye'', Mr Kitto said.
- by Sally Brooker