The multiple benefits of catch crops

Ciaran Collins, Teagasc Tillage Specialist, touches on the many benefits of catch crops and what farmers need to consider when establishing them as part of their ACRES plan.

The fact that cover crops reduce nutrient loss is beyond doubt. Multi-year research in Teagasc has proven that a mustard cover crop reduced mean soil solution nitrate concentrations by over 70% compared to no cover, under both reduced tillage and conventional ploughing.

A cover crop can help to reduce phosphorous run off over the winter. There is little nitrogen benefit to following crops from non-leguminous cover crops such as mustard. However, experiments with leguminous cover crops, clover for example, suggest that they reduce the fertiliser nitrogen requirements of succeeding crops.

Cover crops can also make a valuable contribution to soil organic matter and help to improve soil structure - even if progress is gradual. While there is a cost to establishing cover crops, this can be recouped if they can be grazed by livestock which is also an excellent way to recycle nutrients provided infrastructure like fencing and water are available.

ACRES

Farmers in the Agri-Climate Rural Environmental Scheme (ACRES), who have selected the cover crop option, are required to sow a cover crop before 15 September.

Many tillage farmers entered ACRES and, as part of their plan, selected the catch crop option. ACRES mandates that the seed mixture must consist of at least two species from the prescribed list. The minimum seed rates are outlined in Table 1.

Including three or more seed species will extend the functionality of the mix. Where this approach is followed, at least two seed species from the prescribed list above must be selected using at least the minimum rates. Any additional species may be used at whatever rate the participant deems appropriate. This guidance is equally valid for those not in ACRES. The catch crop must remain in place from the date of sowing until 1 January. After this date, light grazing or incorporation is permitted. No intensive strip grazing or zero-grazing is allowed.

Table 1: List of prescribed catch crops

Table 2: Cover crop groups from the ACRES prescribed list

Cover crop species

It is very important to select cover crop species that suit the rotation. Growers of beans and peas should avoid legumes in their cover crop mixtures and growers of oilseed rape should avoid brassicas. Recent occurrences of clubroot in oilseed rape have been linked to brassica cover crops. Other considerations are winter hardiness and end use. Farmers who intend to graze cover crops with livestock should consider brassicas like fodder rape or leafy turnip.

Sowing date

Early sowing is essential to achieve good autumn growth. An experiment in Teagasc Oak Park examined biomass production from three sowing dates: early – 30 July, target – 18 August and delayed – 8 September. Two cover crops were used: mustard, which is a fast-growing non-legume; and hairy vetch, a winter hardy legume. There was a linear reduction in the amount of biomass produced as sowing date is delayed. The mustard lost 2t DM/ha for each three-week delay in sowing.

Another notable point from the experiment was that there were virtually no weeds produced on the 30 July sowing date. Between 40% and 60% of the biomass was weeds on the 8 September sowing date due to lack of competition from the cover crop. Growers may be concerned with a large volume of biomass, as they try to establish crops in the following spring but in this experiment all of the plots were successfully ploughed without the need for other interventions.

Figure 1: Cover crop sowing date experiment

Grazing cover crops

Grazing of cover crops can increase economic return and is an effective way of recycling nutrients from stock which may leave excreted nitrogen for the subsequent crop. However, there are a few important considerations.

Firstly the infrastructure, water and fencing, must be in place. Soil structural damage is possible, therefore grazing with sheep on light well-structured land is preferred and good grazing management is important to minimise poaching. Shallow, reduced-cultivation sites may have a better livestock bearing strength but grazed cover crops may force the use of deeper cultivation post grazing.

Farmers must comply with conditionality requirements, including GAEC 4 and GAEC 6. You must maintain a grass/vegetated buffer strip of at least 4m along water feature boundaries where non-grass forage crops are being grazed in-situ.

They must also provide an adequate lie back area, which is always accessible to grazing livestock. The lie back area must be grassland. The available lie back area must be at least equal in area to the adjacent non-grass forage area, e.g. 5ha of fodder rape will require at least 5ha of lie-back.

A farmer’s experience

Sam Deane, who farms in partnership with his father Jim, has no stock and is growing spring beans in a field that has been in tillage for over 40 years.

“Up until 10 years ago, the field grew a fairly intensive rotation which included sugar beet and cereals. Our aim now is to gradually improve soil organic matter and soil structure through no-till and catch crops.

“We have evolved to a system which includes no-till and straw incorporation followed by a catch crop. We like a mixture of mustard, which has deep roots and phacelia, which has shallower rooting. Together, these increase soil organic matter and improve soil structure.”

Catch crops require attention to detail if they are to thrive, Sam explained, who added: “We will drill and then roll afterwards to give them a good chance to get going. We think carefully about the coming crops when choosing catch crops. For example, if we are thinking we might grow oilseed rape in two or three years’ time, we won’t use brassicas to prevent the risk of club root.”

Drill

Catch crops are sprayed off at the end of January and Sam says the catch crop residue allowed him to get in at the end of February to drill this year’s spring bean crop. Sam concludes by saying he believes the catch crops are already helping to improve rooting down the profile.

This article first appeared in the July/August edition of Today’s Farm. For more information on Today’s Farm, click here.

Also read: Flexibility granted for shallow cultivation rule