Reduce risk with a two-year break from cereals

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Economic analysis has shown that continuous wheat rotations may be a more profitable option with good seasonal conditions but is a riskier option in poor seasons (Figure 1).

Key points

  • Continuous wheat is a high-risk option for growers in the low to medium-rainfall zones.
  • A two-year break that included a well-adapted grain legume reduced risk while a two-year pasture break was the lowest-risk option.

In low to medium-rainfall farming systems, where cereals tend to dominate, weeds, disease and/or nitrogen can limit cereal yields.

Taking a two-year break from cereals reduces risk by providing an opportunity to control grass weeds and cereal diseases, improving the overall profitability of the system. GRDC research through the Crop Sequencing Initiative (2010–15) demonstrated that a two-year break from cereals improved subsequent wheat yields, particularly when good control of grass weeds was achieved.

Economic analysis

As part of the GRDC’s Stubble Initiative, the Eyre Peninsula Agricultural Research Foundation (EPARF) compared the economic benefits and risk of different crop sequences in low-rainfall farming systems on the Eyre Peninsula over five seasons using average prices. This analysis, by Ed Hunt, shows that including livestock in the farming system can greatly increase farm resilience in below-average seasons.

Graphic showing continuous wheat is profitable in good seasonal conditions but is high risk with low returns in poor seasons, with pasture/wheat sequences a more resilient option in below-average seasons
Figure 1. Continuous wheat may be more profitable when seasonal conditions are good (decile 7 and 9 rainfall) but is a high risk with low returns in poor seasons (decile 1 and 3). In below-average seasons a pasture/wheat sequence (PPWWW) was a more resilient option. SOURCE: EPARF

A two-year pasture break with sheep in a wheat sequence (pasture/pasture/wheat/wheat/wheat) significantly reduced losses in below-average seasons (decile 1 and 3), when compared with continuous-cropping sequences. Continuous wheat had the greatest losses. In a decile 1 year the PPWWW sequence returned $85 per hectare more than the continuous wheat option, which over a 2000ha program equates to $170,000. While this option was the lowest risk, it did not capture all the economic benefit in above-average seasons (Figure 1).

A two-year break with a well-adapted grain legume (field pea/canola/wheat/wheat/wheat) was the reduced-risk option that was also able to capture the upside in above-average seasons. This option reduced losses in below-average seasons compared with continuous wheat and remains the preferred option while legume grain prices are buoyant.

In above-average seasons continuous wheat generated good profits as long as appropriate nitrogen inputs were applied to maximise yield (70 kilograms per hectare in the decile 5 and 7 years, and 90kg/ha in the decile 9 year). But this option had the greatest potential losses in below-average years, making it a risky option.

A low-input option to reduce costs, capping nitrogen input at 50kg/ha, was also trialled. This option failed to reduce risk in below-average seasons and also failed to capitalise on above-average seasons, making it the highest-risk option.

Options

Break crops provide growers with alternative options for weed control, reduced cereal root disease levels (if grass weeds are controlled), increased soil nitrogen (if a legume option is used) and the potential to conserve soil moisture for the next cereal crop.

Managing the factor most limiting to yield is critical to success and growers need to consider break-crop options on a paddock-by-paddock basis for this reason. Choices will depend on the agronomic constraint limiting production (weeds, nitrogen or disease) and other factors such as crop suitability (Table 1).

Table 1 Select break crops based on specific paddock constraints.

SituationCanolaOatsLentils Field peasChickpeas Legume-dominant pasture
I want to control grassy weeds O X O O O
I want to increase nitrogen X X ✓✓
I want to reduce disease
inoculum levels
O O
I have sandy soils O O O X O O
My terrain is rocky O O X X O O
Hay is not suitable for me O X O X O

GRDC Research Codes EPF00001, MSF00003, DAS00119

More information:

Amanda Cook, SARDI
08 8680 6200
amanda.cook@sa.gov.au