In a nutshell...
- Soil erosion is a natural process, where the soil 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 are being undercut by flood water and then collapsing.
- Fences and trees along stream banks fall 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.
- The 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 act as a filter for nutrients. This will remove soluble nitrogen from both runoffs and resurfacing groundwater. 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 hilltops.
- 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 from 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.
Acknowledgements: Dr Richard Chapman, Soil Consultant.