Stopping sediment in its tracks post-winter grazing
Our land management team is urging farmers to take actions to reduce the risk of sediment and nutrient runoff into local waterways following a very wet winter grazing period, particularly in South Canterbury.
Why soil conservation matters
When rain hits bare paddocks following winter grazing, it can wash valuable topsoil and concentrated nutrients like nitrates and phosphorus, as well as E. coli into waterways. These contaminants often collect in gullies, swales or low-lying areas of paddocks — known as critical source areas (CSAs) — and flow into rivers and streams, harming freshwater ecosystems.
“Sediment and nutrient runoff from winter grazing is one of the biggest threats to our vulnerable freshwater fish species, and soil loss can have a high economic cost to the farming operation - that's your fertility getting washed away, that you then have to replace with fertiliser,” said South Canterbury-based senior land management advisor Jess Cochrane.
She said heavy rainfall has resulted in saturated soils, so there’s been more incidences of water pooling and runoff being carried into waterways, in some cases where crops have been grown and grazed through critical source areas.
“This year has really illustrated the importance of identifying CSAs,” she said. ”You might have five years in a row of great winter grazing conditions, where your CSAs never flow – but a year like this shows the importance of keeping them grassed and excluded every year so you'll be prepared for the wet year when it matters the most.”
What you can do to save your soils
Here are practical steps you can take to reduce runoff and protect soil:
- Use straw bales to filter runoff in areas where water is ponding.
- Back-fence wet areas to keep stock out and reduce soil disturbance.
- Minimise machinery tracking across bare paddocks to avoid creating runoff channels.
- Activate your Plan B in wet weather — move stock to drier ground when needed.
- Re-sow paddocks quickly after grazing. Catch crops like oats help absorb excess nutrients and stabilise the soil.
Careful management will keep soil where it belongs
Plan ahead for next winter
Under the national winter grazing regulations, a CSA must remain in grass (not be cropped or grazed) and fenced from stock during the winter grazing period from May through to September.
Jess encourages farmers to start planning now for next year’s winter grazing.
“Take note of where the low points are in your paddocks and where water ponds after rain as these are your CSAs,” she said. “Keep them in grass next winter and leave a buffer between them and your winter crop. Long grass is a natural filter that helps trap sediment and nutrients before they reach our waterways.”
Need help? Head to our winter grazing page or we can put you in touch with your local land management advisor team through customer advisory on 0800 324 636.