Red clover has the potential to fix up to 250kg of nitrogen (N)/ha from the air on an annual basis. This figure is based on swards containing up to 5t of clover dry matter (DM)/ha.

The N fixed from the atmosphere is translocated throughout the growing season to the soil, where it is available to all the plants making up the sward.

Agri-Food and Biosciences Institute (AFBI) grassland agronomist, Dr. David Patterson, discussed the best ways to manage red clover swards during his presentation to a recent AgriSearch webinar.

Specifically, he confirmed that clover will not fix atmospheric N at all if soil pH values are below 5.0.

He said: “Current research is pointing to a soil pH value of 7.0 being optimal when it comes to optimising clover’s ability to take N in from the atmosphere.”

Managing red clover

According to Patterson, weed control is critically important when it comes to establishing and managing red clover swards.

“Weeds can be an issue in the early phases of red clover establishment, particularly if there is a carryover of docks and chickweed from the previous crop.

“The ideal scenario is to have the ground well and truly cleaned prior to sowing. A dock-infested grass field, for example, is not the best starting point from which to establish any kind of red clover sward.

“There is a real limitation on the suitability of post-emergence herbicides. The bottom line that any product used must be red clover safe.”

The AFBI agronomist confirmed that, assuming an effective post-emergent herbicide becomes available in 2024, it should be used between six to eight weeks after the new crop has been sown out.

“The majority of the clover plants must be at the trifoliate leaf stage with docks at a small enough size to be dealt with efficiently,” he said.

“Spraying too early will kill clover seedlings, and spraying too late means that the canopy has closed over,” he said.

Where the management of chickweed is concerned, effective control can be secured by grazing newly established swards with sheep or calves. This must be for a short period of time only.

“Spot spraying of weeds is also feasible in certain circumstances,” he added.

“Another option is to take a very early cut of silage, which will remove a lot of the competition pressure caused by the likes of chickweed,” he said.