Plantain rethink at demo farm
The Lincoln University Dairy Farm (LUDF) is rethinking its approach to plantain, in the face of continued difficulty in realising its expected benefits.
The management team explained the post grazing residual target is now a range of seven to nine clicks on the platemeter, which is 1480-1750kgDM/ha. Prior to this season the rule was seven clicks.
“Those residuals looked the same all season,” farm manager Peter Hancox pointed out. “In summer the ‘steminess’ holds the plate up.”
Lee echoed that.
“To me, the key thing with residual management is you need to link the [platemeter] number to what you actually see and what the cows are telling you. There a no straight lines in a biological system.”
If cows are driven to achieve exactly the same platemeter reading day-in, day-out, throughout the season, the “ramifications” would be quite significant, he added.
Agriseeds’ Graham Kerr chipped into the debate, noting the farm is milking fewer cows but using more nitrogen and growing more grass, so instead of about 4.6tDM of pasture available per cow per year, it’s now about 5.7tDM/cow/year.
“The system has fundamentally changed. Milksolids per cow has gone up significantly. Part of that is because the residual has gone up a bit.
“Perhaps they’re not completely harvesting down to the residuals they were previously but always getting down to 7 clicks is very hard. They’re probably being more honest about what’s actually happened.”
Grazing on a 16-day round – an unusually rapid rotation of the cows around the farm – was also questioned.
“You’ve got to realise for a lot of that period we were growing grass well above demand,” retorted Hancox.
Lee acknowledged if he hadn’t been on the farm, he’d have had the same concern, “but seeing how we were going 16 days was quite appropriate.”
While the mower was out much more often this season, some weeks covering over 50ha, it was either pre or post graze to manage pasture quality. Only about half the amount of silage, compared to the average for the previous seasons, was made.
Lee implied that was a good thing, with pasture growth better matched to demand from the cows.
“This season and last the cows have been much more aggressive in their grazing and intakes have been higher.”
Use of gibberellic acid as a pasture growth promotant was reduced in spring, but ramped up in autumn, partly to fill “a bit of a feed gap,” admitted Hancox, as more supplement than anticipated had been used earlier in the year.
However, besides promoting growth, using more gibb in autumn should “soak up excess nitrogen in the soil. From an environmental point of view that’s no bad thing,” added Lee.
The farm’s used 350kg/ha of nitrogen this season, slightly more than last and a leap on the previously self-imposed limit of 200kg/ha.
With the loss of eco-n and leaching limits looming as the Canterbury Water Management Strategy unfolds, next year use will be reined back to 260kg/ha as part of a suite of measures to try to further cut estimated nitrate leaching to water from the current 26-33kgN/ha.
However, as Ian Brown of Environment Canterbury pointed out to the focus day, even that current figure is a lot better than those estimated for many dairy farms in Canterbury, particularly those on lighter soils.
“This farm has heavier soils and in terms of nutrient loss it’s at the medium to lower end.
“On the stonier soils we’re into 60 to 80kg/ha of N losses. That’s where some of the bigger challenges might be.”
