The South Otago dairy farmers are continuously looking at ways they can grow production and use technology to enhance their business, their cows and the environment.
Judges of the 2009 Otago Ballance Farm Environment Award commented that the Kortewegs sustainably ran an intensive dairy farm that had minimal impact on the environment, and that they had a clear vision and plan for the future.
Mr Korteweg said they entered the competition to show dairying can have a minimal impact on the environment, and they were working to ensure that continued.
The farm is a protected flood plain on the banks of the Matau Branch of the Clutha River, and it has three distinctive soil types.
It was the mix of these soil types and the inability of some areas of the farm to carry cows over winter which encouraged the Kortewegs in 2008 to build their first Herd Home.
They have since added a second.
They ran two herds, with Mr Korteweg saying a single herd larger than 350 caused too much soil damage.
Tile draining was also not an option because there was insufficient fall for the drains to operate, but that lack of fall meant a fine balance between utilising the pasture without damaging the soil.
Mr Korteweg told a recent field day that times had changed.
When he started dairy farming, most farms discharged effluent straight into the nearest river.
He had tested various effluent management systems but now had a three-pond system feeding a travelling irrigator.
It had a $6000 automatic shut-off system which stopped it operating should any problem be encountered such as it travelling too slow, snagging or blowing off a pipe.
It allowed effluent to be spread over 100ha, and an example of the research the family put into new technology were annual soil tests, herbage tests, nutrient budgets and liver biopsies of cull cows which revealed to them the nutrient and trace element status of their soils and vegetation.
The couple began sharemilking 90 cows on a 49ha family farm in 1978-9 and encountered a flood during their first year.
Undeterred, they looked to expand, and in 1981 they bought the home farm plus a neighbouring 15.7ha block, milking 135 cows in an eight-bale walk-through shed.
Over the next 16 years they grew the size of the farm, herd and milking shed and by 2005 they had added another 146ha, including a 31ha runoff, taken their cow herd to 530 and built a new rotary shed.
They also have a 50% stake in a Southland dairy farm.
Part of their success is due to embracing new technology.
As well as the effluent irrigation system, they monitor cow reproduction and pasture performance.
Mr Korteweg said closely monitoring and managing the pasture meant they did not have to top paddocks last season.
They have also installed a ProTrac system in the dairy shed which removes human error from managing the herd.
Cows have electronic identification tags.
Information on those animals that may be being treated with antibiotics, have high somatic cell counts or need to be taken out of the herd, can be programmed in to a computer and those cows can then be automatically drafted.
"It's like having an extra half person in the shed all the time," Mr Korteweg said.
The system cost $60,000 to install but was paying for itself.
The Kortewegs have been regrassing the farm, but in another example of embracing new technology, Mr Korteweg had been trying sugar-grass species and said the cows liked it.
Sugar-grasses tended to also grow as a dense mat which helped with management.
Pasture was direct drilled as the peat soil types on part of the farm were not suited to growing crops and wintering cows.
The Kortewegs realise that as well as being environmentally sustainable, it also has to be socially sustainable, and two of their sons - Blake and Mathew were now involved in the business.
They also have two daughters, Justine, who lives in Canada and Amanda, who lives in Dunedin.