Sustainable farming - soil erosion

In a nutshell...
  • Soil erosion is a natural process, where soils is stripped from the earth's surface and moved to another location.
  • This can be caused by wind, water (rainfall, rivers or the sea) or ice. 
  • Livestock damaging the banks of waterways can also cause erosion.  In 2002 Environment Waikato estimated only 15% of banks were fenced leaving 47,000 km of waterway unprotected from stock.
  • Consequently the moved surface soils do not have any relationship to the underlying rock.
  • These soils are laid down in layers , usually on flood plains and are called alluvial soils.
  • Soil erosion is bad when good farmland is removed and results in environmental damage losing the most important farm asset - the soil.
  • Soil erosion can lead to offences under the RMA.
How can you tell if you have a problem?
 
  • Run-off water in land drains and creeks coloured by soil particles.
  • Drains and creeks that are scoured out after heavy rain.
  • Major and minor slips or slumps on steep hill country and gully sides after heavy rain.
  • Stream banks being undercut by flood water and then collapsing.
  • Fences and trees along stream banks falling into the water.
  • Silting up of drains and streams.
  • Silt arriving on your farm from another farm upstream.
  • Dust storms from cultivated paddocks in hot dry conditions.
  • Soil on arable land banking up against the rows of plants or fences.
  • Water in stock footmarks discoloured by sediment.
How can you tell if you're doing well?
  • Drains and creeks remain clear after heavy rain.
  • No slips or slumps on the farm after heavy rain.
  • Stream banks remain solid after flooding.
  • Trees by creeks remain solid after flooding.
  • Water from drainage outlets is clear of sediment.
What can you do to improve things?
  • Avoid heavy grazing when pastures are very wet.  This will limit pugging damage and damage to soil structure.
  • Provide stand-off areas for stock in winter.
  • Fence off banks of rivers, streams, drains and dams from livestock.
  • Fence and leave a grass filter strip (2 m wide) along the waterway.  This will filter sediment, phosphorus and bacteria from runoff.
  • Fence the waterway margin (2-5m) and plant with native trees and shrubs.  This will provide shade and food for the natural life in the waterway, and habitat for birds and insects.
  • Fence wetlands, swamps and seeps to act as a filter for nutrients.  This will remove soluble nitrogen from both runoff and resurfacing ground water.  It will also filter sediment, phosphorus and bacteria runoff.
  • Do not let stock drink from rivers, streams, drains or dams.
  • Provide a proper water reticulation system for the farm.
  • Prevent stock like deer from fence walking and camping on hill tops.
  • Be aware of how goats can damage steep hill country by lying on bare sunny north facing slopes and digging.
  • Plant appropriate tree species along waterways.  Protect these trees for stock damage.
  • Plant appropriate tree species on steep hill slopes.  Protect these trees from stock damage.
  • Where "gullying" has occurred, make debris/sediment traps to prevent further damage.
  • Don't cultivate steeper slopes and avoid cultivating arable land in hot dry and windy conditions.
Where can you go for help?
  • Regional Councils
  • County Councils
  • Federated Farmers of NZ
  • Ministry of Agriculture and Forestry
  • Department of Conservation
Acknowledgements

Dr Richard Chapman, Soil Consultant.  Phone (07) 829-5437

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