How to manage clover under derogation constraints

The Nitrates Derogation allows more intensive farmers to operate at a higher stocking rate than that stipulated in the Nitrates Directive, subject to adherence to stricter rules to be implemented by the Department of Agriculture.

It will run to the end of 2021 when the fourth programme concludes.

There are over 7,000 intensively stocked farmers availing of the derogation, and, in effect, a farmer must not exceed two dairy cows per hectare without a derogation, but can farm at almost three cows per hectare if approved for a derogation.

Correcting soil pH, the inclusion of clover in swards and grassland management provide a significant opportunity for farmers to maximise the nutrient use of both the organic and inorganic inputs into the farm, while balancing production and the environment.

Within derogation, all new grass reseeding must include a minimum clover content as part of the grass seed mixture; however, the inclusion rate must not exceed 50% of the sward mixture.

According to Bill Reilly, technical representative for Germinal Ireland, there are key techniques and practices farmers should adhere to, in order to utilise the inclusion of clover effectively.

Sowing clover into a new or existing sward

In order for clover to establish effectively in the soil, a pH of 6.3-6.5 is optimum and therefore lime application in sub-optimal pH soils is required prior to sowing clover.

Bill advises that clover be sown into a clean firm seedbed that is ring-rolled prior to sowing and seed is sown at a depth of 5-10mm. As clover growth begins at about 8-10º, clover is ideally sown into a warm soil.

Over-seeding clover into an existing sward is another option for farmers, which can be carried out by slot seeding, direct drill method or broadcast. However, under derogation, and if incorporating clover into an existing sward, this must be done in the same calendar as the original reseed.

Post-sowing fertiliser application should be no more than 40 units of nitrogen (N) per acre, so as not to overstimulate the growth of companion grasses that have been sown with the clover. Bill further recommends the application of phosphate and potash on soil indices <3.

Weed control in a clover sward

As chemistry is becoming more limited, particularly with post-emergence weed control products, the best approach according to Bill is to completely get rid of the old sward prior to reseeding.

By using glyphosate and allowing sufficient time for it to work (five to six weeks) will mean that any old plants are completely eliminated from the sward. This is important so as the new clover sward is not competing with old established grasses in the ley.

Post-emergence sward management practices apply as they would for any reseed. Grazing recommendations state that the sward should be grazed by youngstock once it withstands the ‘pull test’. Grazing a new reseed, where possible, will help ensure a better tillered and denser sward.

In order to reap animal performance benefits in the form of increased milk solid production or increased liveweight gains, 25–30% white clover should be targeted in the sward.

Bill outlines that this performance benefit will be due to increased dry matter intake (DMI), which comes from the inclusion of clover in the sward. He explains that the energy density of clover is higher than that of perennial ryegrasses.

Words of caution when introducing clover to swards

Clover has a tendency to be very dominant in the sward, especially if covers are being grazed very low or being used in a silage sward. Bill recommends that clover is not used in silage swards to avoid this.

From an animal health perspective, Bill also highlights that bloat can be an issue if stock are not used to high levels of clover in their diet, and so they should be introduced slowly to it. Alternatively, stock should be supplemented with a fibre source; such as hay or straw.

Bill warns that extra care should be taken when grazing clover swards on foggy/damp mornings, as the Saponin content of the white clover is increased at that point. This is the compound in the plant that is directly linked to bloating in ruminants.

The Germinal white clover breeding programme is carried out in the Institute of Biological, Environmental and Rural Sciences (IBERS) at Aberystwyth University, where research into improving the physiology of white clover for grazing, for drought tolerance and for improving the phosphorous and potassium use efficiency (PUE) is being carried out.

All Germinal mixtures are available with or without clover. From January 1, 2020, farms in derogation must include 0.6kg clover per acre or 1.0kg coated clover per acre when reseeding.

White, red or a mixture of both white and red clover is acceptable. Germinal mixtures have been developed in line with these derogation guidelines; however, they can be adjusted where required.