CO-EXISTENCE AND CLOVERS
A new generation of clovers could lift producer profits. Harry Hope and
Robert Davies report
IMPROVED white clovers are now available which co-exist happily with each other and their companion grass varieties in productive and persistent swards.
These new clovers secure not only the benefits of free nitrogen fixation (150-250kg/ha/year), superior herbage quality and higher digestibility, but also a more predictable and balanced seasonal contribution to the sward.
These proven claims are made by scientists at the Institute of Grassland and Environmental Research (IGER), Plas Gogerd-dan, Aberystwyth, formerly the Welsh Plant Breeding Station.
"Farmers who specify the latest clover varieties in their seeds mixtures and adopt sward management methods to match their enhanced potential, have nothing to lose but a significant slice of their bill for nitrogen fertiliser," says Dr Ian Rhodes, head of IGERs legume breeding group.
He stresses that the latest varieties are far removed from the outdated Grasslands Huia, included in most seeds mixtures over the last 30 years. Because it was bred for milder climates, this New Zealand strain often suffered from excessive winter kill, particularly in northern and western parts of the UK. Its use also coincided with an era when producers relied heavily on cheap nitrogen fertiliser, contributing to clovers undeserved reputation for unreliability and limited late season production.
"That created a legacy which has still to be broken down," says Dr Rhodes, "but we are now producing varieties which are much more reliable and flexible."
The new clovers can contribute a significant proportion of the sward with a better seasonal spread of production. This raises the nutritive value of the sward while helping the grass to provide bulk yield throughout the growing season. The ideal sward composition contains 30% white clover but this can vary from as little as 5% in early spring to 60% in late summer – useful when the feeding value of the grass component is falling rapidly.
Compatibility of clovers with companion grasses is a major plant breeding objective at IGER. Different combinations of clover and grass strains can yield exceptionally well or poorly together and research efforts have been focused on identifying the underlying causes. Differences between strains in root and shoot characteristics affect the ability to use light energy, available soil nutrients and water resulting in complementary or antagonistic growth rhythms. Selecting specific traits in the new clover varieties and matching them with compatible grasses provide seed mixtures which result in a vigorous and stable sward.
Dr Rhodes explains that clover yield in a mixed sward depends on the ability of its stolons to spread throughout the sward. The yield potential of the clover is then expressed as the total length of stolon per unit area and leaf production per unit length of stolon.
Researchers have shown that there is a strong link between the total length of stolon/unit ground area surviving through the winter and spring growth – resulting in a major effect on total annual yield. Poor spring performance of some clovers reflects stolon kill in winter, but this can be overcome by selection for winter hardiness.
Breeders at IGER have introduced this valuable trait into the varieties AberCrest and Aber-Herald, with AberHerald showing particularly rapid growth at low spring temperatures. The effect of this selection for winter hardiness and low temperature growth is shown in the table (below left).
"Cold tolerance is quite easy to breed for but should not be confused with the ability to grow at low temperatures," explains Dr Rhodes. "Both qualities are needed in a productive variety. AberHerald with its thick and profuse stolons is showing terrific adaptability in terms of early spring start and exceptional cold tolerance, while AberCrest is in an intermediate position."
• Compatibility with grasses in the sward.
• Improved resistance to cold stress.
• Flexibility in response to grazing by cattle and sheep.
• Nitrogen fixation and total sward yield response.
• Seed yield and ease of harvesting.
• Reduction in bloat risk.
Winter damage and low temperature growth
Clover varietyStolon length/unitLeaf yield/unit stolon length
ground area m/sq mat 6C (mg/mm)
AberCrest: New variety with extreme cold hardiness.
Huia: Most commonly used general purpose variety.
AberHerald is showing good growth despite the severe 95/96 winter.