This harvest will see the planting of over 16,000ha of cover crops on more than 3,500 tillage farms in Ireland. And these figures are likely to increase further next year on tillage farms that may be tight on “Landscape Feature” ecological focus area (EFA), should the EU decide to increase the EFA requirement to 7% of the arable land area next year. But, for the moment, tillage growers must prepare their cropping plans and have their cover crops for 2016 established by 15 September.

Benefits of catch/cover crops

The main benefit of sown catch crops is to prevent nutrient loss (mainly nitrate) by leaching over the winter. This is the technical definition of catch crops (to catch nutrients), while cover crops are defined as covering the soil for an even longer period to prevent damage by winter rainfall. Because there are different definitions in the EU and because these influence the dates for which they are obliged to exist in aided schemes, we in Ireland have opted to go with the catch crops definition.

Research by Dr Ritchie Hackett at Oak Park has shown that the yield benefits recorded in crops of spring barley (after growing cover crops) are variable, often small and sometimes negative. This concurs with findings in other European countries. For the pure tillage grower, the main aim is to use cover crops to achieve a more friable surface structure for drilling, in both autumn and spring, and to improve soil organic matter levels.

The growing of cover crops in conjunction with the use of organic manures should help to restore more bacterial life in soils and to increase earthworm populations. On mixed farms with sheep, cover crops may be grown for forage using fodder species and then grazed by hoggets or in-lamb ewes after 1 December. This can help reduce feeding costs and shorten the wintering period for this enterprise.

List of recommended catch crops

The list of recommended catch crops permitted to be grown under GLAS is outlined in Table 1. These catch crops, from a rotational perspective, can be divided into three distinct cropping families:

  • Brassicas.
  • Legumes.
  • Grasses/cereals/borage.

    • It is important for farmers using rotations to exercise care in choosing the components of a catch crop mix for planting.

    Crop type, seeding rates and establishment methods for GLAS

  • Must sow at least two catch crops from the cover crop species outlined in Table 1.
  • The first two species used must be sown at the minimum seed rate (Table 1).
  • All additional crop species and rates are at a farmer’s own discretion.
  • All seeds must be broadcast or direct drilled. Ploughing is not permitted as an establishment method.

    • Effect of sowing date on autumn cover crop growth rates

    Early planting is important and all crops must be sown by 15 September, which has been set as the latest date. But earlier than this is very much to the grower’s benefit as the planting date is heavily related to the volume of canopy or organic matter produced.

  • One day’s growth in July is equivalent to a week’s growth in August.
  • One week’s growth in August is equivalent to a month’s growth in September.

    • If your planting date is delayed into September, a general rule of thumb would be to only drill a cheap mix at time of year (see mixes in Table 2).

    Crops to avoid

    General rules need to be followed when choosing the species to include in the catch crop mix.

  • Avoid grain rye or grass rye in a cereal rotation.
  • Avoid all brassica species in a mix where you have oilseed rape or beet in a rotation.
  • Do not use any of the legumes where you grow peas or beans in the rotations.

    • Recommended fertiliser rates

    As the objective of catch crops is to capture free nutrients in the soil to protect them from leaching, fertiliser use should only be considered where grazing is a secondary objective for the crop. Be aware of the following:

  • Catch crops sown before 15 August for grazing require 50N:12P:25K to feed their growth potential.
  • As the catch crop is the second crop grown in the year, there is no requirement for buildup rates of P or K.
  • There is no fertiliser recommended on catch crops not to be grazed or those sown for grazing after 15 August.