There are many thoughts on the best way to destroy cover crops at this time of year, in preparation for spring drilling.
Depending on the crop type, how well it has grown or the drilling system, there are various ways of dealing with the destruction of the crop.
Many farmers have opted to graze them off with light cattle and sheep. This is a very good way of recycling the crop and nutrients back into the ground.
However, it is not without its risks to soil structure.
Overgrazing or use of ring feeders can cause poaching, which can be difficult to rectify in the short-term.
Strip or block grazing tends to reduce soil compaction or run-off issues.
Methods of destruction
According to Teagasc, the use of glyphosate before ploughing for the next crop is the most common method of destruction.
But if there are significant numbers of volunteer cereals in the cover crop, growers may be harbouring diseases like net blotch, rhynchosporium, take-all and/or aphids.
Ideally, six to eight weeks should be allowed after the application of glyphosate before a crop is ploughed-in. This will help to reduce the risk of direct transfer across to the new crop.
Growers using direct-drill systems are normally planting directly into cover crops and then ‘burning them off’ with glyphosate.
This method has many benefits, assuming the drill can handle the cover crop. This approach helps soil structure while also reducing weed competition.
However, if there are significant numbers of volunteer cereals in the crop, then the risk of increased disease and barley yellow dwarf virus (BYDV) pressure is enhanced in the following cereal crop.
Dealing with cover crops
Teagasc points out that, whichever system is used, growers must have a plan to deal with their cover crops. Otherwise, the benefits of growing them in the first place will be reduced.
The autumn of 2021 proved to be very favourable for the growth and development of green covers on stubble fields. There was exceptional growth from natural regeneration to planted cover crops.
Teagasc sampled a number of green covers during December 2021, in order to assess their nitrogen (N) content.
This analysis has confirmed that 10-50t/ha of fresh material can be produced, containing 12-70kg N/ha.
Earlier-sown cover crops produced larger green covers compared to later-sown cover crops / natural regeneration.
Research would indicate that up to 40% of the plant N may be available to the following crop.
Crops such as peas, beans or vetches produced the highest levels of plant N, offering the greatest opportunity to reduce chemical N rates in the following crop.