Chemical topping is proving a cost-effective way of increasing the quality and quantity of pastures on uncultivable parts of Hamish and Annabel Craw’s Banks Peninsula farm.
Our four-part series looks at how the trial went and what management changes the Craws have made.
The couple, who farm 422ha at Little Akaloa on the northern side of Banks Peninsula, have been trialling different chemical options to control poor quality native grasses and allow clovers to flourish and fix nitrogen (N).
A new way forward
While chemical topping is nothing new, they have been trialling new chemistry in conjunction with grazing management practices to build the legume content of the sward on their higher hill country. Effectively lifting the energy value – or ME (metabolizable energy) – of the pasture. This work is being carried out through Beef + Lamb New Zealand’s Innovation Farm programme.
Speaking at a recent Innovation Farm field day, Hamish says they are very aware that it is the energy made available to animals through forages that drives livestock performance and ultimately, the profitability of their business.
The value of legumes
Several years ago they created a system using high ME legumes – namely lucerne and clovers – on their easy “point country” and it’s a system that is proving very efficient.
They are achieving average weaning-weights of 35kg from lambs off this country so are now shifting their focus to their middle hill country, knowing that improving the energy of the pasture would drive ewe lactation and pre-weaning growth rates in lambs grazing these areas.
“We weren’t satisfied with the legume content in our hill country pastures; they were dominated by poorer grass species and having seen the value of legumes on the easy country, we wanted to increase the quantity of legumes on our hill country,” says Hamish.
While mindful of the value of increasing the ME of their pastures, the couple is also aiming to lift the quantity of drymatter grown by 3T/ha and believe this will be achieved by getting more legume-fixed nitrogen into the system.
Chemical control
Rather than just introducing new clovers, the couple wanted to promote the existing, naturalised clovers such as subterranean clover, by chemically removing competing, poor quality grass species and managing the legume to allow it to set-seed and regenerate.
Through the Innovation Farm programme, the couple were given the opportunity to work alongside scientists and agronomists to determine the best chemical options – including rates and timings – to control these poor-quality grasses without harming the clover.
Testing chemical options
In the first year of the three-year programme, the project team set up small trial sites and tested various chemical control options, specifically looking at a light chemical top, a heavy chemical top and grass eradication.
Grass eradication using Valiant (active ingredient haloxfop-p) emerged as the preferred option, so in year two, they continued with the plot trials looking at different rates of Valiant to determine the most cost-effective and effective grass-control option.
In year three, the chemical trial was up-scaled to a hill country block and Valiant, applied at a rate of 500ml/ha, was used in conjunction with grazing management to allow existing clovers to proliferate.
A success story
In the first winter following a December spray, the Craws noticed a lot of clover in the ground and in the spring of 2015 had a clover-rich sward in the treatment area – which is exactly what they were aiming to achieve.
“Typically, in our environment, we start to lose pasture quality in November and December, now we are retaining that quality for longer and that is the key,” says Hamish.
At the start of the programme, legumes only made up 8% of the sward, by using Valiant they have pushed this up to 30-40% of the total sward, significantly increasing the ME of the pasture.
This success has given the couple confidence to carry on with the spray programme, although they admit that once they have sprayed the grasses out, the challenge will be to retain the clover at that 30-40% level. This is where grazing management comes in.
