Jane Chrystal, B+LNZ’s Principal Science Advisor – Farm Systems & Environment, says the interim results of a Landcare Trust/AgResearch study ‘Understanding the impacts of sheep wintering’ reinforced the value of leaving critical source areas (CSA) ungrazed to help trap and retain sediment and contaminant run-off resulting from winter grazing.
Under good practice winter grazing management, CSAs, which are low-lying areas within a paddock such as depressions, gullies and swales, should be fenced off and left ungrazed until spring or summer. Ideally, the areas should be left in grass which acts as an ideal filter and sediment trap.
Jane says early results from the trial comparing contaminant loss and sediment trapped on similar paddocks, one where the CSAs were grazed while the other was ungrazed, were consistent and significant.
While both paddocks were sown in kale and under a similar management regime of top-down grazing and two breaks of five days, there was a marked difference in the amount of suspended sediment in the water samples collected from each paddock after rainfall events.
Even before analysing the suspended sediment data, the scientists found visually striking evidence of the immediate effectiveness of the CSA on reducing the loss of soils from the paddocks.
The report states that ‘these visually striking differences provided an immediate indicator that the CSA was having a demonstrable impact on retaining soil and sediments eroded from the uphill portions of the paddock.’
Subsequent analysis of the suspended sediments from all rainfall events throughout the winter of 2021 supported these results.
Jane says the trial, which started in the winter of 2020, is being run on a commercial farm in Waitahuna West Otago with the goal of understanding the impacts of winter sheep grazing management on several environmental indicators.
“These results highlight the importance of keeping stock away from CSAs during winter and valuing these areas for their ability to prevent soil and contaminant losses.”
Jane encourages all farmers growing winter forage crops to work through the Forage Cropping Management Plan which is a chapter in B+LNZ’s Farm Plan or available as a stand-alone resource.
“This plan will help farmers identify their risks and plan how they will make the best use of their winter feed resources while protecting their environment and animal welfare.”
- Forage Cropping Management Plan (PDF, 2.3 MB)
- Read more information on preparing forage crops for grazing (PDF, 546 KB)