If you have struggled to
maintain clover in grass
swards, but want to reap
the benefits, it could be
worth seeking a new
variety better suited to the
farms conditions, as
Robert Davies found out
INTEREST in clover has never been stronger and a wide range of climate adapted varieties are already available for a variety of farm conditions and management systems, according to a plant breeder.
Michael Abberton, head of legume breeding at the Institute of Grassland and Environmental Research, say that this list is also set to grow.
Already there are several new white clovers in the pipeline, including one very large leafed variety, so the differing requirements of producers will be satisfied, he adds.
Many producers still express some concern about the persistency of white clovers, especially under intensive management systems where significant inorganic nitrogen is applied.
A long-term trial at IGER Aberystwyth has looked at clover yield and the total yield of grass/clover swards managed in different ways. The experimental plots were sown in July 1991, in three fenced off blocks, each receiving a different nitrogen fertiliser treatment.
The blocks consisted of three randomised replicate plots of nine white clover varieties. These were Aran, the very large leafed variety, AberCrown, Nesta and Olwen, which have large leaves, the small leaf sized AberDai, AberVantage, AberHerald and Menna, and small leaved AberCrest.
On each plot the clover variety was sown with 20kg/ha (8kg/acre) of the intermediate perennial ryegrass variety Talbot. The three nitrogen treatments were no nitrogen, 100kg/ha (80 units/acre) and 200kg/ha (160 units/acre) each year.
Samples were taken at a height of 3cm (1.2in) at six week intervals and plots were grazed intensively by sheep for about seven days after sampling. This infrequent grazing was most appropriate for large and medium sized varieties.
Nitrogen was applied in equal amounts five times a year, starting in March and continuing seven days after each cut. Maximum and minimum temperatures and rainfall were recorded daily. The figures show that the greatest climatic impact on the experiment was the low rainfall in the summer of 1995.
Dr Abbertons overall conclusion was that white clover made a significant contribution to total sward yield at all nitrogen application levels in all years. In nearly all cases the clover content of swards was above 20%.
New medium leaf size varieties bred for yield, persistence, flexibility, cold tolerance and nitrogen tolerance performed particularly well, as did Aran. For instance, AberVantage had an average clover content of 50.6% with no nitrogen, 38.6% with 100kg N applied/ha (80 units/acre) and 26.9% when the dressing was 200kg of N/ha (160 units/acre).
Under the no nitrogen regime the average yield of the nine varieties was higher in year eight than in the first year, after which yield of some varieties declined. However, new medium leaf size varieties still yielded up to 3.5t/ha (1.4t/acre) after 10 years without added nitrogen.
Nitrogen fixation by clover allowed total yields to increase to 9-10t/ha (3.6-4t/acre) a year. When 100kg N/ha was applied average white clover yields were maintained above 2.8t/ha (1.1t/acre) for most of the experiment, with the better varieties still yielding 2-3t/ha (0.8-1.2t/acre) in year 10.
Mean grass/clover yields were only marginally higher than from varieties getting no bagged nitrogen. The performance of new medium leaf size varieties AberDai and AberVantage was outstanding. They were the most productive varieties at the end of the experiment, with yields still reaching 2.3t and 3t/ha (0.9t and 1.2t/acre), respectively.
Applying 200kg N/ha did suppress clover yield, but Aran, AberHerald and AberVantage still produced 2t/ha (0.8t/acre) year at the end of the trial. In year 10 the average total yield was 10.5t/ha (4.2t/acre), or only 1.6t/ha (0.65t/acre) greater than when no nitrogen was applied. Clover contents remained steady throughout the experiment.
"The results show clearly that, under rotational sheep grazing, modern varieties of white clover can make a constant, reliable contribution to yield and forage quality," says Dr Abberton.
"At the same time white clovers fix considerable amounts of nitrogen, allowing savings in fertiliser use for at least 10 years. In the time that this experiment has been underway at IGER further developments and progress in white clover breeding have been made."
PROGRESS has also been made in red clover breeding, which restarted at IGER three years ago, after a 15-year gap.
Two promising new varieties based on work done before breeding was suspended, are under evaluation. One of these has a high oestrogen content and will be suitable for speedy lamb finishing.
But Mike Abberton and his team are even more excited about a new programme which will put significantly superior red clover varieties on the market in about six years time. These will be based on genetic material which promises enhanced grazing tolerance, improved winter hardiness and possible resistance to pests and diseases, including sclerotinia, or clover rot, and stem eelworm.
"Red clover has tremendous potential as a silage crop, but we need to improve its tolerance to grazing after the last silage cut." This means understanding the physiology of plants crown, he adds. Breeders are working with their colleagues in molecular biology and animal science in a multi-disciplined approach to the production and management of improved varieties."
This is necessary to ensure that the protein production potential of red clover is used over several seasons and not squandered by breakdown in the silo.
"The use of DNA markers can speed up selection, and our system of evaluation under farm conditions will give producers varieties they can make the most of." *
New white and red clover varieties will increase the number of farms that can grow crops, says Michael Abberton.
• New varieties developed.
• Climate apapted.