Guidelines for catch crop species

Some growers may have to plant catch crops this autumn to provide green cover for greening compliance. A few will need to plant 100% of their cropped area as their equivalence measure for crop diversification, while up to 200 need to do this to provide their ecological focus area (EFA). But those who signed up for catch crops under GLAS will not be obliged to plant this autumn, because their applications will not be cleared in time.

At a recent Teagasc open evening on the farm of Eugene Ryan in Laois, it was stated that only growers using catch crops to provide either equivalence or EFA for greening will have to actually plant them this autumn.

However, Teagasc’s Richie Hackett suggested that all growers considering catch crops in GLAS should plant a few strips of different mixes this autumn to learn the potential merits and demerits of different species in a mix. There is also a need to get experience on how best to plant and handle the crop for subsequent replanting.

It was stated that 1,060 tillage farmers indicated their intention to plant catch crops under GLAS when the scheme opens. Based on the maximum payments allowed, this could equate to up to 14,000ha of catch crop as early as next autumn.

Teagasc’s Ivan Whitten emphasised the importance of farmers knowing what they want catch crops to achieve for them, as this is critical in helping select the most suitable species.

Basic rules

The same basic rules apply to all the GLAS catch crop schemes. They must be planted before 15 September and be left in situ until 1 December. They also specify the species that can be grown and the fact that plough is not allowed for establishment. But there are also growers who will plant catch crops without support payments and this is not bound by any regulations, which leaves the grower with more flexibility on what and when to sow, and when it can be removed or incorporated.

Oats and common vetch could be a useful catch crop mix where there is rape in the rotation:

Planting catch crops within GLAS schemes entitles the grower to a payment. For general scheme planting the payment rate is €155/ha/year, which sets a maximum of 32ha that can be supported at this level. But where catch crops are being planted as an equivalence or EFA measure, this payment is reduced to €128/ha (maximum 39ha supported).

Where a grower has been given priority access into GLAS for greening, the minimum area that is supported is 10ha. But where growers are not impacted by a greening requirement, then the minimum area that can be supported is 4ha.

As well as specifying the crop species that can be planted, a minimum seed rate is specified for each species sown alone (Table 1).

However, mixtures of at least two species must be planted and the seeding rates that apply in a mixture have not yet been agreed. They need to be seriously adjusted if some species are to survive and prosper in a mixture.

While this list is relatively limited, the Department will consider other crop species providing prior approval is obtained. All of these species have different characteristics and effects in terms of their root systems in the soil, their impact on insect and bird biodiversity, and their effects on soil structure, whether or not they produce nitrogen, etc.

There will also be big differences between varieties within a species. Advice at the Teagasc open evening was that the mixtures should initially be kept simple.

Planting

The crops that we saw in Laois were sown on 24 May and were very full, with lots of biomass. But for those planting now, after a main crop, moisture can often be limiting and so seedbed quality is very important.

For the GLAS schemes, catch crops must be planted using some form of mini-till rather than ploughing, so machines must have good soil firming capacity and the roller is still important. Planting depth will vary within species, but most will benefit from drilling rather than broadcasting.

Timelines of planting are critical to generate autumn fodder or biomass. Input level is guided by the end use of the crop so fodder crops will be fertilised, but this is seldom justified for catch crops. Generally, most of these crops will not go to seed when planted in the autumn, but some of them could flower if planted after winter barley, or even earlier. If flowering occurs in rape or radish crops, these should be topped to prevent seed formation. Other practical considerations mean that conventional oats can carry a big risk of BYDV infection with early planting, which would have implications for all other cereal crops sown locally that autumn.

A few other points to note. Phacelia must be covered post-planting as it will not germinate in the presence of light.

Phacelia becomes a visibly dominant species in a mix as it is a good nitrogen scavenger, but it must be prevented from going to seed. Seeds must be covered at drilling:

Buckwheat must also be covered for germination. Failure to cover the seeds could result in poor establishment or seeds germinating at a future point, creating a problem.

Fodder mixes

There were quite a number of different crop mixes planted at the site and Helen Wilson of RAGT spoke about the different mixes and individual species. It was stated that the planting of a catch or fodder crop, whether fertilised or not, does not impact on the soil nitrogen index rating for the following crop.

The first specific mix we looked at was a 60:40 mix (by seed weight) of fodder rape (Barcoli) and leafy turnip (Vivant). As well as being among the cheapest of the mixes present, this mix is very fast to establish, it is winter hardy and it can be grazed. Helen said that the ratios in this mix are not critical, but they should be avoided where brassica crops are grown in the rotation.

Leafy turnip is quite like tyfon and it’s very good for fattening lambs. A number of people present warned that grazing should finish well short of flowering, and that for sucklers it should finish well short of calving, as it is not properly balanced with minerals. For this reason, use of these species better suits dry stock rather than pregnant animals.

The earlier catch crops are planted, the more bulk will be produced. Teagasc’s Christy Watson said that a previous trial of fodder crop production showed that dry matter yield halved with every two weeks of delayed planting (see Figure 1).

Fodder rape was described as a 12-week sprinter (growth-wise) and then it slows down. The reason being that it will quickly use up all of the available nutrition in the soil and then be forced to slow down, unless there is sufficient added fertiliser available.

This mix, which grows very rapidly post-planting, provides a great way to mop up nutrients in the soil. And this leafy vegetation has a low carbon-nitrogen ratio and so will break down quite quickly when incorporated, to provide recycled nutrition for the following crop.

Another simple mix was provided by oats and common vetch in a 40:60 ratio. This option may prove popular in that it is easy to establish. However, if it is sown before September, black oats should be used because they are less prone to all disease threats. It is important to have enough vetch in the mix and not too much oats so that the vetch is not smothered out early.

Green manures

Most of the mixtures on display were designed as nutrient catch crops and soil conditioners. Some of the species included should not be fed to animals or they will not willingly consume them (eg mustard).

One such mix contained Ethiopian mustard plus Berseem or Egyptian clover in a 55:45 ratio. Helen said that the Ethiopian mustard is deeper rooting than other mustards, but that seed is also more expensive. The Berseem clover is regarded as quite competitive and its roots will be shallower than the mustard. In winter, the frost will slow down or kill this clover.

A single plant of Berseem clover surrounded by taller, stemmy Ethiopian mustard:

All clovers and legumes are slow to get going post-establishment, so they need to be planted early to deliver value. Richie Hackett from Oak Park said that recent research on a number of autumn-sown legumes (which did not include Berseem clover) found that hairy vetch and winter peas resulted in a considerable amount of nitrogen (an estimated 80-100kg/ha) for the following crop.

Another mix contained phacelia, forage rape and Berseem clover in a 25:15:60 ratio by weight. The amount of rape has to be kept low because it is so vigorous post-establishment. But once phacelia gets established, it too becomes a dominant species. Phacelia needs to be sown relatively early as it needs warmth to thrive.

Dave Barry from Goldcrop told us that bees love phacelia when it is in flower, but that it should not be allowed to go to seed so as to prevent future problems. If phacelia gets to 40% flowered, it is recommended to top or incorporate it.

In this mixture, the fodder rape provides the deeper root system to act on the soil beneath. And the Berseem clover will contribute some nitrogen fixation.

Mixtures

There were many other mixtures on display, all of which were constructed to provide balanced foliage growth along with varying root structures. Mix ratios are not fixed, but they need to be balanced in favour of the slower establishing species.

In general, leafy turnip and fodder rape are sprinters – they grow vigorously post-emergence to consume all available fertility and then slow down. For this reason, management must be adapted (eg fertilisation) for a mix that is sown for fodder versus nutrient trapping.

Depending on the mix, the inclusion of a nitrogen-fixing species can help support the growth of other species in time, but these are generally slower to get going post-establishment. Where possible, a proportion of any mix needs to be vigorous post-establishment to help cope with weeds.

A number of the seed companies like Goldcrop and Germinal will sell formulated mixtures for specific purposes. It is sensible to stay with one of these until you get familiar with the different species.

Other species

White mustard (yellow flower) is the cheapest of the bunch and has very vigorous early growth. This means it can take over in a mix, so the seeding rate needs to be adjusted down. It does not have a very deep rooting system. Ethiopian mustard is deeper rooting, tends to be more erect, suits in mixtures with legumes, but it is more expensive. Mustards are also being bred to deliver other characteristics.

“Some of the breeding effort is targeting high glucosinolate content to promote nematode resistance,” Helen Wilson stated.

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