What are the benefits of break crops in a stubble-retained system

Photo of four different crop types
Break crop trial at Eurongilly, NSW. Photo: Tony Swan, CSIRO.

In a stubble-retained farming system cereal stubble can allow the build-up of weeds and diseases. Break crops provide a unique opportunity to target pests, weeds and diseases and address nutrient deficiencies. But to get the most out of a break crop it is important to know what you are trying to achieve.

What are the key factors limiting cereal crop production?

Look at your particular situation to identify the key factors limiting cereal productivity (Table 1):

  • If grass weeds are the main issue choose a competitive break crop with suitable grass‐selective herbicide options
  • If nitrogen fixation is needed consider a legume
  • For disease issues grow a grass-free break crop.

Table 1. The key factors limiting cereal productivity will influence the choice of break crop.

Key limiting factor

Break crop options

Grass weeds

Canola, hay oats, legume-dominant pasture, fallow and pulse crops

Cereal diseases

Canola, hay oats, grass-free pasture, fallow, vetch and pulse crops depending on the specific disease pressure

Low soil nitrogen

Legume-dominant pasture, vetch and pulse crops

Poor soil moisture

Fallow or a spray-topped legume

Marketing and prices, soil type, machinery and crop use (grain, grazing or hay) will also be important in determining the break crop options in the rotation.

While break crops can be perceived as higher risk in medium to low rainfall areas the Eyre Peninsula Agricultural Research Foundation Inc (EPARF) has demonstrated that a one or two year break can be more profitable than maintaining a continuous wheat cropping sequence.

What are the benefits of break crops?

Trials have shown that break crop profitability is largely determined by the benefit in the productivity of cereals grown after the break. The benefits of improved weed control can make break crops very profitable compared with continuing with high grass weed populations in cereals.

Managing grass weeds

Break crops provide more options for diversity in herbicide and non-herbicide weed control. For instance, by growing a broadleaf crop provides the flexibility to use chemicals grass-selective herbicides that are not suitable for use in cereal crops.

When weed control is the major issue, trials have shown the wheat-yield benefits of a break crop are greater from a two-year break compared to a one-year break.

Managing diseases

Grass and cereal free break crops of medic, canola or pulses will not only reduce cereal disease inoculum for soil-borne cereal diseases such as take‐all, CCN and rhizoctonia, but also fungal diseases carried over by spores on cereal stubble such as yellow leaf spot and white grain.

A single, non-cereal crop free from grassy weeds can dramatically reduce rhizoctonia inoculum levels to a lower disease-risk category compared to a cereal crop, however these only last for one cropping season.

Nitrogen

A legume break crop will improve the nitrogen supply to the following cereal crop. On average, 20 kilograms of nitrogen per hectare is fixed for every tonne of legume shoot dry matter produced.

Other considerations

Sowing break crops into retained cereal stubble provides early protection of both small plants and soils from wind damage. Cereal stubble provides a trellis to enable pulse crops to grow taller and more erect plants, which can help with harvestability.

Including break crops within crop rotations may increase pest levels. Chemical control options may be necessary to control the pests in break crops depending on seasonal timing, pest density and other beneficial insects in the system.

More information

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