In practice farmers are likely to get a 25-30% reduction in nitrogen leaching – good news for farmers given impending nutrient loss rules that will require some farmers to dramatically cut leaching rates.
Similar reductions might also be possible for fodder beet although there are more provisos with that crop because including oats in the cropping programme will delay sowing of the fodder beet.
There are provisos for the kale-oats-kale sequence but studies done over three years on Lincoln University’s Ashley Dene farm as part of the wider Pastoral 21 programme have shown the cropping sequence is practical, cost-effective and achieves significant environmental benefits.
The leaching results have come from a detailed study done by Lincoln University PhD student Peter Carey, supervised by Lincoln University professors Keith Cameron, Grant Edwards and Hong Di. Cameron said the results from the trial work were being shared with Overseer and its advisory team and developers.
Carey’s study involved lysimeters, or columns of soil, being taken from Ashley Dene to the university where drainage measures could be taken.
Urine was collected from cows grazing on a kale crop with oat silage as their supplement at Ashley Dene and analysis done to determine the nitrogen concentration.
The urine was applied to the lysimeters to mimic deposits by cows in June with oats crops then sown 21, 42 and 63 days later.
Sowing the oats crop 21 days later gave a 40% reduction in inorganic nitrogen leached but the scientists haven’t included that result in management guidelines because it’s unlikely farmers would get the crop in by that time.
The results concluded farmers could reduce nitrogen leaching losses by 25-30% compared with leaving the area fallow after grazing until September or October.
“Given that the best reductions in nitrate leaching are from the earlier-sown oat crops the advice would be to not necessarily wait until the cows had left the whole winter grazing area altogether.
“If soil conditions are suitable, then the oats could be sown into smaller areas as cows work their way through the crop or move from paddock to paddock,” Cameron said.
Getting into a paddock straight after cows have been grazing can be challenging although the free-draining soils at Ashley Dene make it easier.
Cameron and Pastoral 21 colleagues, Lincoln University professor of dairy production Grant Edwards and DairyNZ principal scientist Dr David Chapman, said further work could be done to look at ways to establish the crop and measure its ability to mop up excess nitrogen in heavier soil.
Oats was ideal because it grew at cooler temperatures, making it winter-active and hungry for nitrogen when there was a higher likelihood of rain, drainage and leaching losses, Cameron said.
Because they weren’t harvested until the end of November the establishment of the next kale crop was delayed, which limited kale yield by about three tonnes drymatter (DM)/ha but also meant irrigation or reliable rainfall was needed over the establishment period.
Grown on its own, without oats, kale produced an average 13.5t DM/ha over the three-year study at Ashley Dene. If it was grown in a sequential cropping rotation with oats, the delayed establishment, even with irrigation, meant the kale yield dropped to an average of 12t DM/ha.
But the oats crop produced an average 7.6t DM/ha giving a total annual DM production of about 18t DM/ha.
Over the three year period the kale-oats programme grew 3-7t DM/ha/year more than kale-only.
The cost of the systems was similar, with the kale-only programme coming out at 21c/kg DM, plus or minus 4c, and the kale-oats programme coming out at 19c/kg DM, plus or minus 4c.
The detail of the financial analysis and important provisos to ensure the gains are achieved can be found on DairyNZ’s website.
