The judges praised the couple, who they said achieved a balance between high milk production and careful environmental management of their riverside property.
Judges also commented on their attention to detail in managing nutrients and effluent to avoid damaging the soil and river.
An example was building a herd home, or wintering shelter, for cows to avoid damaging the soil over winter.
It was so successful a second structure has been built for this winter.
The Kortewegs milk 540 cows on their 180ha farm, a protected flood plain alongside the Clutha River, on which they produce between 220,000 and 225,000 kg milk solids (kg/ms) a year.
They also won the dairy farm award and nutrient management award.
• Other winners in the Ballance competition were - Land and life award: Alan and Jean, Richard and Abby Hore, Beaumont Station, Millers Flat; livestock farm award: Hamish Erwood and Janet Templeton, Waitahuna; sustainable resource management award and innovation award: Bruce, Denise and Cara McGill, Owaka; habitat improvement award and harvest award: Allan Roulston, Balclutha.
The Southland Farm Environment Award winners named on Wednesday night were Vaughan and Megan Templeton, who run a 425ha dairy farm east of Riverton.