Grain legumes can deliver an extra 1t/ha yield to wheat crops

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Australia’s broadacre farming is dominated by wheat, traditionally in rotation with legume-based pastures grazed by sheep, but increasingly in continuously cropped systems.

The most widely grown broadleaf break crops have been lupins (in Western Australia) and canola (throughout southern Australia), although other grain legumes such as field peas, chickpeas, faba beans and lentils are also grown on soils to which they are adapted.

The benefits of break crops to following wheat crops have been studied and reviewed extensively since the 1990s. 

As part of the GRDC Crop Sequence Initiative, more than 900 experimental comparisons were reviewed to quantify the yield benefits delivered by break crops. 

The results showed that, on average, wheat yields increased by 0.5 tonnes per hectare following oats, 0.8t/ha following canola and 1.0t/ha following grain legumes (0.7 to 1.6t/ha) compared with wheat on wheat. 

Although the yield benefit was variable, yield was rarely reduced. The average yield benefit was also constant across the full range of wheat yield, whether 1.0t/ha or 6.0t/ha.

This ‘break-crop effect’ often extended to a second wheat crop in the sequence, especially following legumes (benefit of 0.2 to 0.3t/ha), but rarely to a third except under dry conditions. 

These benefits to subsequent cereal crops can influence the economic advantages underpinning the adoption of break crops, especially where break crops are considered more risky or less profitable than the main cereal crop. 

It is vital to consider the economics of break crops over a full two to three-year sequence and to account for the value of diversifying income to manage price variations. Profitable rotations need sound business decisions provides a basic profitability assessment of break crops.

These benefits can only be captured if break crops are well managed. A weedy, low-yielding legume or canola crop is not a break crop, as weeds will host cereal diseases and set seeds that emerge in subsequent cereal crops, and nitrogen (N) fixation by the legumes will be poor.

In WA the average benefit to wheat crops from lupin break crops doubled, from 0.5 to 1.0t/ha, from the 1980s to the 1990s as growers improved the management and increased the yields of the lupin crop. 

Until recently the focus of break crop use and research in Australia was largely for disease control and nitrogen supply. They were generally grown according to the N or disease status of the soil, both of which can now be measured pre-sowing to help with crop sequence decisions. 

The costs of maintaining an intensive cereal system in terms of N fertiliser and fungicides could be compared with the various break-crop options. However, the emergence of herbicide-resistant weeds (especially annual ryegrass) as a result of intensive cereal production with selective herbicides has become a game-changer, and now dictates crop sequence decisions for many growers. 

A focus on the utilisation of break crops as part of the integrated management of herbicide-resistant weeds has became a new focus for research.

Photo of man knelt in field pea crop

Victorian Mallee grower Rob Heinrich relies on field peas as a disease and weed break in his family farming enterprise

PHOTO: Brad Collis

Legumes shine bright at Rainbow

By Rebecca Jennings

With no livestock in his system, break crops play an important weed-management role for Victorian Mallee grower Rob Heinrich. Rob, a third-generation grower who farms with wife Helen and son Anthony, 24, at Rainbow, north of Horsham, has grown legumes for more than 20 years.

He typically crops 400 hectares of field peas, 100ha lentils, 360ha wheat, 500ha barley and 120ha triticale. It is a mix that balances soil type (for example, triticale performs better in lighter soil than wheat) and works well in a cereal/cereal/legume rotation.

The Heinrichs grow Parafield peas and red lentils (PBA FlashA and Nugget), and have sold to Melbourne-based food manufacturer Ward McKenzie for the past 20 years.

While the area has a historical average annual rainfall of 350 millimetres, Rob revises this back to 200 to 250mm based on the past few years. A dry finish to 2014, with no in-crop rain after August, saw reduced yields. While field peas can yield up to 2.5 tonnes/ha on the Heinrichs’ farm, in 2014 they averaged 1.4t/ha.

Rob recalls how, in his early days of growing pulses, they were not a profitable crop. Although today, solid prices (lentils as high as $900/t and peas more than $400/t during the 2014 harvest) ensure break crops are a profitable choice.

While the economics make sense to Rob, he says the longer-term benefits of break crops are certainly in the paddock.

“I find a one-year break crop provides sufficient weed control. It really makes a difference to ryegrass and brome grass, which are our main challenges,” Rob says. “Without a grazing option, our business relies on the pulses as a break for cereals – they really lift the paddocks by fixing nitrogen and also help control disease.”

When asked about challenges associated with growing pulses, Rob is clearly happy with this link in his crop cycle. He credits direct drilling with overcoming previous issues with establishing the crop.

Frost is the major issue, with 30 per cent damage to the field peas last year.

More information:

Rob Heinrich,
aurelia13@bigpond.com


More information:

Dr John Kirkegaard, CSIRO,

john.kirkegaard@csiro.au

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