Teagasc highlighted the value of cover crops within a tillage rotation at this year’s National Ploughing Championships at Ratheniska, Co. Laois.
They act to soak up nutrients that, otherwise, would leach out into watercourses.
But to have the desired impact, the crops must be planted within days of the previous harvest.
Teagasc research has confirmed that cover crops will act to reduce leaching rates from fields.
Given the weather that has impacted on the country over recent weeks, 2023 has turned out to be challenging for tillage farmers, from every perspective.
In theory, the earlier that cover crops can be sown out in August, the better.
This approach ensures the maximum benefits to the next crop while also minimising nitrate losses from the soil.
Teagasc is also confirming that dry matter (DM) losses of up to 2t/ha will be accrued in the event of a two-week delay in sowing out cover crops from early August through until early September.
Cover crops
In terms of using cover crops within a specific arable rotation, there are certain pitfalls to be avoided.
E.g., brassicas should not be included within a cover crop mix if oilseed rape features within a rotation. Such an approach is likely to enhance problems with clubroot.
In addition, legumes should not be included in a cover crop mix that immediately proceeds a crop of beans.
If it is a case of growing spring barley after spring barley, then farmers have a lot more freedom in terms of what plant mix would work within a cover cropping scenario.
The tailored inclusion of legumes within a cover crop mix can act to take nitrogen (N) out of the air and deposit the same crop nutrient into the soil.
Decisions
There are many different reasons why cover crops may be suitable for a farmer and this will depend on what the farmer is trying to achieve.
This could be: Improving crop productivity; improving soil health; building biomass; capturing carbon; soil protection over the winter; reducing run-off; preventing nutrient loss; or as part of an environment scheme.
One of the main functions of a cover crop is to mop up any remaining nutrients especially nitrogen after the previous cereal crop.
On free-draining sites prone to nitrate leaching, research has shown that overwinter green cover can substantially reduce nitrate leaching to ground water from fallow crop land.
A cover crop will also have beneficial effects in terms of soil structure improvements and protects the soil from potential phosphorus loss through surface run off over the winter period.
Research at Oak Park, Co. Carlow has shown that, in general, the effects of cover crops, compared to bare fallow or natural regeneration, on yield of succeeding cereal crops under Irish conditions are variable, often small and sometimes negative.
However, significant yield benefits in succeeding crops through the use of cover crops occurred infrequently. This concurs with findings in other European countries.