"What we are talking about here, it's hard, it takes time, and it's complex."
Encouraging farmers to see certain operational changes as "a growth and development opportunity for all of us", Ms van Reenen outlined a number of strategies to help ensure a more sustainable future for farmers.
Stocktakes of land, soil and water were vital steps to creating a useful future plan for any farm, she said, as well as keeping accurate nutrient budgets to assess environmental impact.
Ms van Reenen also explained the benefits of properly matching land class to land capability.
She cited the example of one farmer who spent a lot of time clearing an unused area of his land in an attempt to make it suitable for pasture - only to conclude it was actually more cost effective to let the area revert to shrub.
Since every property was different, farmers should be prepared to be flexible and dynamic, Ms van Reenen suggested.
"It's not a one-size-fits-all approach," she said. "[It's] not just doing it because dad did it."
Although she conceded that implementing new sustainability strategies were often "not cheap", Ms van Reenen was hopeful about the future of farming in the Lake Rotorua catchment.
"I'm yet to meet a farmer that doesn't want to leave their land in a better state than what they got it in ... well I have met one, but luckily he's not here today.
"I challenge you now to consider what my children coming back here in 40 years time will be talking about and what role you can play."
Mark Shepherd, a senior scientist at AgResearch, used his presentation to feed back the latest results of the Pastoral 21 research project into low nitrogen input dairy systems. The project, funded by a number of partners including DairyNZ and Fonterra, uses small farmlets in four locations across the country to investigate whether a lower nitrogen input system can be as profitable as a higher input one.
Dr Shepherd said results from the project had, on the whole, been positive. "We have got measurements, we have got modelling, and that gives us confidence," he said. "We should be able to maintain profit or close to our profit, and that is generally shown to be true."
He said that at one of the four test areas, in Waikato, reducing the average number of cows per hectare from 3.2 to 2.6 had managed to cut the level of nitrogen fertiliser used per hectare from 150kg to 50kg - a significant efficiency improvement.
One method to reduce nitrogen leaching was to regularly stand cows off the normal grazing paddocks, which was easier to achieve during the autumn and winter months.
"Putting less nitrogen through the cow, we're going to be getting less out of the back end," Dr Shepherd said. However, as with all great plans, there was a familiar caveat. "They do need a good level of management."
