There are many different reasons why cover crops may be suitable, and it all comes down to what the farmer is trying to achieve, according to Teagasc tillage specialists.
This could involve:
- Improve crop productivity;
- Improve soil health;
- Build biomass;
- Capture carbon;
- Soil protection over the winter;
- Reduce run off;
- Prevent nutrient loss;
- To partake in ‘greening’ and GLAS.
One of the main functions of a cover crop is to mop up any remaining nutrients, especially nitrogen, after the previous cereal crop.
Ideally, they should be sown in August for maximum dry-matter accumulation and for soil-nitrogen retention.
Farmers who opt to use these crops to satisfy ecological focus areas (EFA) requirements are obliged to sow them this autumn before the latest sowing date of September 15.
The cover crop will also have beneficial effects in terms of soil-structure improvements and it protects the soil from potential phosphorus loss through surface run off over the winter period.
Cover crops research
Research in Oak Park has shown that, in general, the effects of cover crops – compared to bare fallow or natural regeneration – on the yield of succeeding cereal crops under Irish conditions are variable, often small, and sometimes negative.
Significant yield benefits in succeeding crops occurred infrequently, the research found. This concurs with findings in other European countries.
Cover crops planting
When planting cover crops, early sowing is vital to achieve good autumn growth. Growers should aim to sow in mid to late-August or the first week of September.
Crops sown after mid-September are unlikely to produce much growth.
Mixtures of at least two species are required for GLAS and an EFA. Mixtures that contain a legume (e.g. vetch, peas) are more likely to give a yield benefit in succeeding crops.
Growers should avoid complicated mixes particularly where such crops are being grown for the first time.
It is important to avoid using species that could cause problems in the rotation (e.g. brassica cover crops in a rotation containing oilseed rape.)
Cover crops can be grazed from the beginning of December. If grazing is an objective farmers should choose species that are suitable for grazing (e.g. forage rape, leafy turnip, fodder radish, oats, and peas).
Ploughing to establish cover crops is not allowed for GLAS or EFA purposes.
Growers should use either use a drill capable of sowing into stubble, or broadcast the seed and lightly cultivate before rolling. If different sized seed are being broadcast, it may be appropriate to broadcast the large and small seed separately.
Establishment rates will normally be lower for broadcast crops.
If cover crops are not being grown for grazing purposes, applying fertiliser is not going to give an economic benefit.