AFBI and CAFRE CloverCheck – an aid for the management of grass and white clover swards
Interest in the ability of white clover to supply nitrogen to grassland has been increasing over the past year or two due to large increases in fertiliser price. The use of grass/clover swards is compatible with maintaining a stock carrying capacity equivalent to grass swards receiving up to 200kg nitrogen per hectare per year.
However, many farmers do not have experience in managing grass/white clover swards. As a starting point AFBI and CAFRE (College of Agriculture, Food and Rural Enterprise) have been providing data on growth rates and clover content of grass/white clover swards as ‘benchmarks’ for farmers. Since 2005, AFBI and CAFRE have run a project to assess grass/white clover growth and clover content on swards throughout the Province. While these are mainly on organic dairy farms, they do also cover an organic and a conventional beef farm. The purpose was to develop methods which would be used to monitor grass/clover plots laid down on swards in fields and to regularly publish these results. A further aim was to predict the likely progress in growth and clover content over the following two weeks on these plots.
In the spring of 2008, CloverCheck was set up to supply information on grass/clover plots and the surrounding paddocks on four organic dairy farms. The information collected every two weeks and the prediction for the next two weeks on clover content and growth of the plots and fields was presented on the CloverCheck page within the organic section of the Rural Portal. In all, 11 bulletins were published during the growing season.
The average clover content of the plots and fields are presented in Figure 1.
Average clover content in plots and fields at 4 sites.
Clover contents were generally good this year. The warm, dry, but late, spring resulted in clover content in plots fenced off in the paddocks reaching 65% when sampled in early July. Thereafter, the prolonged period of wet weather for the rest of the summer and autumn resulted in a steady decline in content until sampling ended in mid-October. As expected, clover content in the paddocks was lower than in the plots but followed a similar trend with maximum clover content reached in July. A clover content of 40% on a paddock or whole field basis is considered exceptionally good. Despite these high clover contents, bloat was not a concern on any of the four farms.
Daily growth rates of the grass clover swards on plots, cut every 4 weeks, (Figure 2) were particularly high throughout May. As the plots are on organic farms they received only organic manures, mainly slurry and applied in early spring. Despite receiving no inorganic fertilisers the average growth rate over all four sites in May was over 90 kg DM (dry matter) per hectare per day. A combination of heavy yields earlier and the drought extending into June produced relatively low growth rates in June-early July. The prolonged wet soil conditions during the remainder of the summer and autumn made management of the swards difficult. However growth rates in late July reached 65 kg DM per hectare and kept above 40 kg DM per hectare well into September.
Average growth rate of grass/clover swards in plots at 4 sites during 4 weeks prior to sampling.
In the CloverCheck bulletins a mathematical model predicted how the swards on average would perform over the following two weeks, using weather forecasts. The model was able to inform farmers in advance:
about the unseasonably low growth in swards in June due to the continued drought
that clover contents would not be set-back due to the drought and
that the clover content of the paddocks would become progressively lower than that of the corresponding plots, due to the continued wet weather.
As already stated, grazing during wet soil conditions has a damaging effect on white clover. However, a heavy herbage cover carried into and through winter can also harm clover in the following year. It is important therefore that grass/clover swards are grazed down in late autumn-early winter, taking care not to cause undue damage.
For further information please contact:
by Dr Scott Laidlaw, AFBI Crossnacreevy and Manus McHenry CAFRE Greenmount Campus