The value of protecting critical source areas in intensively grazed winter forage crops was highlighted in a sheep winter grazing trial carried out over three years on an Otago farm.
Run by AgResearch and supported by industry stakeholders including Beef + Lamb New Zealand, the Ministry for Primary Industries and the NZ Landcare Trust the ‘Understanding the impacts of sheep winter grazing’ project looked at grazing practices and the impact these had on contaminant losses.
The researchers found that where critical source areas (CSAs) were left ungrazed, there were significantly fewer contaminant issues than when they were cropped and grazed.
Water sampling showed a reduction of approximately half in the amount of phosphorus sediment and E.coli in overland water flows compared to control areas where the critical source areas were grazed.
The paddocks where the trial was run over 3 winters between 2020-2022 covered two very similar catchments. CSAs were identified and in-field measuring equipment was installed before forage crops, namely swede and kale, were planted and grazed. Good wintering management practices including leaving CSAs in grass and ungrazed, directional grazing and back fencing, were implemented in the catchments over different years and compared to the catchments with no protection of the critical source areas. Samples were captured during run-off events over each winter and spring period.
The findings reinforced the value of leaving CSAs in grass and ungrazed, but also found that grazing and treading pressures on the soil were low compared to cattle grazing, and this allowed rainfall to infiltrate the soil.
Nicole Foote, NZ Landcare Trust’s Regional Coordinator for Otago, said this is the first-time data specific to the impact of sheep winter grazing had been collected.
While winter grazing is known to make a significant contribution to total losses of contaminants transported from land to water, there had been very little information available that documents losses under sheep grazing.
“The research provides invaluable information for farmers looking to improve their land management practices and minimise environmental risk.”