South Canterbury arable farmer Andrew Darling says an on-farm trial where wheat yields were unchanged despite a significant drop in nitrogen rates has given him the confidence to continue to cut back.
Darling told a Foundation for Arable Research field day on his farm that he was looking to become more sustainable in terms of crop inputs even before the sharp rise in nitrogen fertiliser prices, which have at least doubled in the last two years.
Darling and his wife Amy lease Poplar Grove Farm at Kingsdown, just south of Timaru, from his parents Warren and Joy Darling.
Darling is the fourth generation on the farm, made up of a 250 hectare home block and a 250ha leased neighbouring property.
The mainly dryland rolling downs property grows feed wheat, feed barley, oil seed rape, turf grass and sometimes sunflowers.
Nitrogen is now the farm’s single biggest cost.
The Darlings have invested in tools and technologies including a Yara N-tester, a hand-held leaf N measurement tool used to identify the N requirements of plants. This is used as a calibration tool for sensor cameras on the roof of their tractor, which automatically varies nitrogen application rates depending on a crop’s density and greenness.
The Darlings have also been 1ha grid soil sampling for the last seven years.
For the 2020 harvest, the Darlings relied on the N-tester for applications on two replicated strips in a wheat crop, with the remainder of the paddock receiving a standard application.
The crop yielded 12t/ha across the paddock, regardless of N application rate. Grain protein was also the same despite 120kg of urea/ha less being applied in the trial area.
The reduced rate areas used 16.5 units of N per tonne of yield compared with 21 units under a standard application.
Buoyed by the results, the Darlings have done the opposite this year.
Instead of trialling 2ha, they have applied N under variable rate over the whole farm, apart from a few strips in wheat and barley given a standard blanket application as a comparison.
FAR senior researcher cereals Jo Drummond told the field day that farmers and growers associate reduced N rates with reduced crop yields and profits, but it is possible to reduce N without reducing profit.
It was a matter of keeping a crop green “enough” by understanding the supply and demand requirements, knowing what N was in the soil now and what would mineralise through the course of the season.

• By Pat Deavoll