It's touted as the unsung hero of New Zealand pastoral systems, yet farmers are taking white clover for granted – at the risk of reducing feed quality and animal performance, writes Sarah Gard.
White clover is the country's most important legume due to its nitrogen-fixing abilities, persistence and high feed value.
Animal performance has been shown to improve by up to 50 per cent with increased clover content in pasture.
It is also the most widely sown pasture legume in New Zealand farm systems.
The country's high-quality primary products are internationally competitive due to a predominately ryegrass and white clover pasture mix, which responds favourably to our temperate climate.
According to the Ministry for Primary Industries, more than half of New Zealand's 27 million hectares of land is used for agriculture and forestry and, in turn, around half of this land is improved pasture.
However, intensification of farming during the last 20 years has seen the sector become preoccupied with the speed of pasture renewal, at the expense of quality.
Farmers are so focused on extracting every kilogram of dry matter they can, that the significance of white clover is being overlooked in favour of the grass component in pasture mixes.
I regularly meet farmers who increase their grass sowing rate just so they can get to their first grazing faster, despite the fact that the increased plant competition will have a negative impact on clover establishment.
The optimal white clover percentage for animal productivity benefits is 20 to 30 per cent, and around 30 per cent for dry matter yield performance.
While many farmers will be able to tell you these figures, a combination of lighter sowing rates for clover (generally in favour of the grass component), increased use of nitrogen fertiliser (in the pursuit of high dry matter and animal production), and soil nutrient deficiency means the majority of New Zealand farms have a clover percentage of considerably less than 30 per cent.
DairyNZ reports clover usually contributes less than 15 per cent of annual dry matter in New Zealand dairy pastures.
White clover's significance lies in its ability to provide free nitrogen, ultimately reducing a farmer's reliance on artificial fertiliser.
The potential nitrogen fixation rates from white clover are upwards of 300kg N/ha/year, depending on several factors – including the farm system, soil pH, and the 16 nutrients required for the optimal growth of white clover.
However, increased fertiliser use in intensive farming systems is suppressing white clover's natural nitrogen-fixing ability and ultimately resulting in lower pasture productivity.
Average nitrogen fixation from white clover in New Zealand is only 185kg N/ha/year.
Agricultural sustainability is now a mainstream priority.
The impact of nitrogen leaching on New Zealand's freshwater quality is a leading headline and topic of debate. Greenpeace is calling for a ban on synthetic nitrogen fertiliser in New Zealand, staged nitrogen reductions are being enforced throughout the country, and a new survey by Fish & Game indicates that freshwater pollution is top of mind for New Zealanders.
Within this landscape, it is inevitable that farmers will need to reduce their nitrogen applications. White clover, a natural nitrogen-fixer, presents a practical and cost-effective solution that can help reduce environmental impact while maintaining productivity – farmers just have to remember to look after it properly. Sowing rates, establishment periods and soil nutrient profiles all need to be considered.
White clover is also renowned for its persistence, largely due to a superior root system, which makes for a more resilient plant.
Many of the farmers who use our white clover varieties are located in regions subject to environmental extremes. Hamish MacKenzie of Braemar Station, for example, uses a white clover permanent pasture mix to increase feed quality and persistence for the farm's 7000 sheep, 1500 deer and 450 cattle.
Braemar Station is located 700 metres above sea level on the eastern side of Lake Pukaki in the South Island. The high country property is subject to temperatures of minus 15 degrees Celsius in the winter and drought conditions in summer. The pasture therefore has to survive and tolerate such seasonal extremes.
Ultimately, pasture quality plays a significant role in improving animal output and farm productivity.
In recent years we have seen an increased emphasis on, and return to, a 'pasture first' approach. The initiative, which aims to match feed demand with supply, is being led by DairyNZ.
White clover's role in this regard should not be overlooked.
A key challenge is reminding farmers of the significant benefits that this important legume brings for long-term soil fertility and pasture performance.
- Sarah Gard is General Manager for seed company Germinal New Zealand.