Mixing tetraploid perennial ryegrass with a diploid offers exciting potential to produce the same or more milksolids from fewer cows, with easier pasture management.
On many farms, this tetraploid/diploid ryegrass mix is now the new normal, striking a near-ideal balance between pasture palatability and robustness, and growing more energy (MJME) per ha than straight diploid perennial ryegrass.
Ultimately, as has already been the case on Lincoln University Dairy Farm, such tetraploid/diploid pastures could help farmers reduce their stocking rate, fertiliser inputs and overall environmental footprint without affecting total MS production.
So what’s the secret?
New tetraploid Viscount - replacing the previously successful Bealey - has excellent DM yield and year-round growth, but the attribute that really stands out on farm is their palatability: animals love them.
Many farmers are happy sowing straight tetraploid ryegrass pastures to take advantage of this palatability; many others have tried but haven’t been able to achieve the persistence they want. Adding diploid Trojan changes the dynamic.
Trade-off in pasture mix
The resultant tetraploid/diploid mix is an average of the two types, denser and more robust than a straight tetraploid, and much more palatable than a straight diploid.
“For those who want tetraploid-based pastures, but who have struggled getting straight tetraploids to persist, this gives a strong option. The tetraploid/diploid mix is a significantly more persistent,” says pasture systems expert Graham Kerr.
Key benefits are higher animal performance and easier pasture management, particularly for residual management.
For example, after diploid perennial ryegrass exceeds 3200 kg DM/ha cover, it becomes less palatable to animals at the base of the pasture, and grazing it to a good even residual typically leads to reduced MS production.
Add tetraploid Viscount to the mix however and cows will graze the combination well even at higher covers of 3500-3600 kg DM/ha, making it very forgiving during periods of peak daily pasture growth rates.
It also allows farmers to run higher average pastures covers, which in turn drive higher overall pasture yield.
“This is the old adage ‘grass grows grass’ in action. For example, at LUDF widespread use of tetraploid/diploid pasture mixes has allowed the farm to raise pre-grazing covers by 400 kg DM/ha, and contributed to about 1 t DM/ha/year extra.”
The reason for this is the tetraploids softer stems. Unlike diploid ryegrasses, which become fibrous and chewy as covers exceed 3000 kg DM/ha, tetraploids remain easier for cows to eat and digest at the same length.
What’s happening within the pasture is ryegrass tillers are grown out to three full leaves tiller, rather than previous 2 to 2.5, so you capture the higher pasture growth rates achieved at higher covers.
Graham Kerr says where persistence is the top priority, straight diploid pastures might remain the best bet.
“But I think the tetraploid/diploid mix presents some really interesting opportunities in the dairy industry to lift profitability, through decreasing stocking rate and increasing per cow performance.
“If we can produce the same or more milk off fewer cows there are great savings in per cow costs, and in rearing young stock. The environmental footprint is likely to decrease too. Handling weather extremes also become easier with less stock.
“The LUDF is a great example of this. Compared to 6 years ago, it now has 17% fewer cows (560 compared with 670), but on average cows are producing 25% more with less nitrogen fertiliser and fewer supplements.
“The extra palatability of the tetraploid/diploid pastures at LUDF has been part of enabling cows to eat around 250 MJME/day at peak, rather than the 210 MJME/day they consumed five years ago.”
Barenbrug has tested a range of different tetraploid/diploid perennial ryegrass ratios on farm, and as a result recommends sowing half the normal sowing rate of each cultivar.
That equates to about 15 kg/ha Viscount (half of 30 kg) plus 10 kg Trojan (half of 20 kg). Sown with appropriate clovers this mix gives the balance of palatability and persistence to improve the amount of ME/ha eaten across many situations.
“And in case you’re wondering if Viscount simply gets ‘grazed out’, the answer is no. Within the pasture the 4000-5000 tillers/m² are intertwined and animals cannot separate them.”