According to Teagasc, cover crops represent an opportunity to improve soil structure and rotation-related diversity.
A cover crop – sometimes called a catch crop – is sown between two main tillage enterprises. Planting takes place normally during the autumn / winter period.
It is important to establish cover crops rapidly after cereals have been harvested, in order to get the full benefits from the new enterprise in terms of soil nutrient and carbon capture.
Cover crops maintain a green cover on land, thereby mopping up nutrients left over from the previous growing season.
Cash crops, on the other hand, are grown to feed animals, usually over the winter period.
They can be grown between two main tillage crops and usually receive nitrogen (N) , phosphorous (P) and potash fertilisers or manures to maximise dry matter (DM) production.
These crops are generally grazed or harvested over the winter.
It is important that fodder crops are not planted beside rivers/open drains as they are generally harvested during the winter. This can lead to sediment and phosphorus loss: cover/catch crops are more suited to these locations.
Cover crops
As a cover crop establishes in the soil, it generates a large root system which recovers N that has been left over from the previous crop.
If there is little or no green cover in a field over winter, this N can be leached from the soil and lost to ground water or streams, leading to poor water quality – therefore a cover crop with a large and deep root system is best.
The cover crop stores the N it recovers from the soil in its above ground biomass over the winter until it’s incorporated back into the soil in spring.
The N recovered by the cover crop adds to the soil organic pool and will become slowly available to the subsequent tillage crops over time.
Increased root volumes generated by cover crop breaks up the soil layers. This improves soil structure leading to increased stability and improved drainage.
Roots also represent a source of organic matter. The cover crop also provides exudates which feed the soil biology.
This process is critically important as it orient the soil’s sand, silt and clay particles into water-stable packets, which keep their structure when wet.
One of the major threats to tillage productivity world-wide is the loss of soil organic matter. This is the main store of plant nutrients in the soil, especially soil nitrogen.
Organic matter also helps to reduce soil compaction as it acts like a shock absorber between the soils particles: sand silt and clay.