The trial, done at DairyNZ’s Scott Research Farm by senior scientist Dr Sharon Woodward, was established to determine whether mixed pasture could increase milksolids production and improve nitrogen efficiency.
“Cows fed on mixed pasture excreted half the amount of nitrogen (N) in their urine compared to cows on standard pasture,” Woodward said.
“Reducing N losses has implications for greenhouse gas emissions and nitrate leaching.”
In the trial both the standard and mixed pastures were sown with perennial ryegrass and white clover. The mixed pastures were also sown with lucerne, chicory, plantain and prairie grass although the prairie grass was quickly ruled out because it didn’t perform.
The cows on the mixed pasture ate less than those on the standard pasture.
“Although the cows on the mixed pasture ate less they were more efficient as they produced at least as much milk and sometimes more milk. This, of course, means more milksolids, not only because of the increase in volume but because we sometimes got an increase in milk protein concentration as well,” Woodward said.
Total cumulative drymatter yields were similar for both pasture types although the pattern of growth was different. There were advantages in feed availability in summer and autumn from the mixed pastures, however, this yield advantage did not persist in winter, Woodward said.
Pasture performance has been interesting, especially during the recent drought.
“At the height of the drought the lucerne with its deep root system had no problem surviving the dry and acted as a shade, protecting the ryegrass. Ryegrass in the mixed pasture remained at a reasonable length and was a lush green whereas in the standard pasture the ryegrass was stunted and brown.
“We were achieving significant differences in drymatter production with the mixed pastures and still achieving pasture covers close to 2000kg DM/ha.”
Although species like lucerne, chicory and plantain in the mixed pasture do not grow as well during the winter, they have bounced back by summer during the first three years of the trial.
Woodward said the performance of the mixed pasture during the drought highlights the potential of increased pasture diversity providing other options for farmers in meeting the challenges of adverse climatic conditions.
The biggest finding from the study, however, was that feeding mixed pastures had a major impact on reducing urinary N losses and this was achieved with no loss in milk production.