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Bespoke approach to break crop selection in southern LRZ

SARDI research officer Sarah Day outlined LRZ break crop selection work at the GRDC Grains Research Update in Adelaide.
Photo: Clarisa Collis.

A bespoke approach to sequencing - tailoring crop species and varieties to individual farming systems - can consistently lift break crop performance in cereal-based rotations.

This is the finding of trials in the southern low-rainfall zone (LRZ) as part of GRDC-invested research in partnership with the South Australian Research and Development Institute (SARDI), University of Adelaide and agribusiness consultancy Rural Directions.

SARDI research officer Sarah Day, who led the study, says a break crop has the potential to increase the yield of the following cereal crop by one tonne per hectare and improve the profitability of a cereal-dominant farming system by up to $100 per hectare a year.

But these sequential gains in productivity and profitability depend on break crop performance, which is typically 'highly variable' across the LRZ of southern Australia, she says.

Performance consistency

Now recasting break crop consistency in rain-limited farm businesses, however, is new data gleaned from trials at 14 locations across the southern cropping region (with four main long-term trials at Minnipa, Willowie, Warnertown and Pinnaroo, South Australia).

The trials, from 2017 to 2019, examined chickpeas, vetch, lentils, lupins, field peas, faba beans and canola in a three-year rotation (break crop/wheat/wheat).

"Previously break crop development largely occurred in medium and high-rainfall zones," Ms Day says.

LRZ break crop development

The study represents a step-change in LRZ break crop development in that it could help growers match sequencing options, including crop species and varieties, to specific on-farm conditions, she says.

These conditions include climate, soil type and biotic stresses, such as weed and disease pressure.

"The on-farm objective for growing a break crop guides selection," she says.

For example, the objective for including a break crop in a cereal-dominant rotation might be weed or soil-borne disease management, increased water-use efficiency, improved soil fertility, expanded crop diversity to help minimise seasonal and market risks, or long-term system sustainability.

Grain and biomass yields

Ms Day says that, overall, field peas emerged from the study as the most stable break cropping option for southern LRZ areas. This finding was based on the consistency of field pea grain and biomass yields.

"However, field pea for grain production is a risky option where spring frost events occur frequently," she says.

On the other hand, this versatile legume can help curb farm business losses resulting from seasonal risks, such as frost.

This is because pulses - such as field peas, vetch, lupins and faba beans - have end-uses ranging from hay and forage to silage and manuring that can salvage a financial return where break crops are frost or drought-affected.

The study shows faba beans are suited to frost-prone areas, as they are more frost-tolerant during the sensitive reproductive phase than other pulse break crops, Ms Day says.

In situations where weeds and herbicide residues are management objectives, herbicide-tolerant cultivars developed for faba beans, lentils and canola can help manage these constraints.

"Canola also has a good fit in farming systems where cereal root diseases limit crop productivity," she says.

Ms Day says the study found chickpea performance was relatively stable in terms of its grain and biomass yields in the northern Mallee region, but the potential high cost of disease management is an important consideration.

The trials show lupins are well adapted to sandy and acidic soils, but lentil performance was low on these soil types, plus the crop's low plant height limits its harvestability.

Profit-risk profile

Ms Day says the research also highlighted the profitability and risk of different break crops grown in a three-year-rotation.

This was based on analysis of 5000 seasonal outcomes for crops grown in clay loam and sandy loam soils using a model developed by Rural Directions to assess risk and net profit.

It showed that, overall, chickpeas were the most-profitable, lowest-risk break crop option - which was largely driven by high commodity prices and low disease pressure.

Chickpeas averaged a gross margin gain of $282/ha/year and a net profit of $182/ha/year.

"Sequences that included chickpeas were profitable in 56 per cent of years," Ms Day says.

"But it is important to note that the analysis was based on a low-input system, in which only one fungicide spray was applied.

"Chickpeas would not be as profitable in a season with high pressure from disease, such as Ascochyta blight."

The @RISK model found vetch hay and lentils were also profitable break crop options. These crops were ranked second and third overall respectively for their low-risk, high-profit profile.

On average, vetch hay returned a $178/ha/year gross margin and a $78/ha/year net profit. This break crop was also profitable in 57 per cent of years.

Ranked the third-most-profitable, low-risk option, a lentil break crop averaged a gross margin of $173/ha/year and a net profit of $73/ha/year. Lentils were profitable in a three-year rotation in 52 per cent of years.

Lupins and field peas were also profitable, but faba beans and canola were unprofitable, high-risk options. For example, lupins were profitable in 44 per cent of years and field peas were profitable in 40 per cent of years.

The average net profit for each year of the rotation was $24/ha for lupins and $4/ha for field peas.

Faba beans and canola were only profitable in 34 per cent and 39 per cent of years respectively. The average net profit loss for each year of the rotation was $10/ha for faba beans and $44/ha for canola.

High-performance varieties

The GRDC-invested research also identified high-performance varieties for break cropping in the southern LRZ.

This ranking of three to six varieties for each break crop - canola, chickpeas, faba beans, field peas, lentils, lupins and vetch - was based on grain and biomass yields, and gross margin returns at four SA trial sites.

Ms Day says the fast-growing, early maturing Nuseed® Diamond variety emerged as the top-performing canola cultivar.

Its performance was followed by Pioneer® 44Y90 and Pioneer® 43Y92, which can assist with weed and herbicide residue management.

High-performance chickpea cultivars were the desi chickpea variety PBA Striker and the kabuli variety Genesis 090. These cultivars outperformed the large-seeded kabuli chickpea PBA Monarch.

PBA Samira and PBA Marne were the top-performing faba bean varieties. PBA Bendoc also showed potential as a Group B herbicide-tolerant option for management of broadleaf weeds and herbicide residues.

PBA Butler and PBA Wharton were the highest-yielding field pea varieties.

These cultivars achieved similar yields, but PBA Butler was favoured by its early vigour and canopy structure.

The trials showed that irrespective of end-use, semi-leafless (SL) field pea varieties were better suited to low-rainfall systems than conventional (C) field pea varieties - with relatively low lodging resistance and no biomass yield advantage.

PBA Bolt and PBA Hallmark XT lentil varieties showed high performance across all the trials.

Of lupin varieties, the new high-yielding, early flowering PBA Bateman cultivar was the most consistent performer.

The top-performing vetch variety was the early maturing Volga cultivar.

More information: Sarah Day, 08 8841 2404,

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