South Australian soil health strategy prescribes crop diversity

Companion cropping one of five soil health-sensitive measures at Pontifex Farming

Agronomy
Companion cropping is a long-term investment in soil biological health for South Australian grower Grant Pontifex. PHOTO Matt Turner

Companion cropping is a long-term investment in soil biological health for South Australian grower Grant Pontifex. PHOTO Matt Turner

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The Pontifex family grow a mix of companion crops on SA mainland and island properties.

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For the Pontifex family - Grant, Ben, Jodie and Sarah - companion cropping is part of a multi-layered strategy to lift soil health on 7000 hectares spread across three properties in South Australia.

Two of these properties, totalling 4700ha, are located at American River and Vivonne Bay on Kangaroo Island, while a third 2400ha-property is located at Paskeville on the Yorke Peninsula.

Grant says companion cropping is one of five soil health-sensitive measures that aim to improve biological soil health, particularly its soil organic carbon content and water-holding capacity at Pontifex Farms.

Other components of the family's integrated strategy implemented in the past 15 years include organic fertiliser applications (chicken manuring), ground cover cropping and zero-till practices with emphasis on crop residue retention.

It is a combination of cultural practices that, to date, has increased soil organic carbon from 1.5 to 2 per cent (soil organic matter), and boosted crop water use efficiency from 12 to 18 kilograms per millimetre, he says.

Of this "long-term investment" in soil health, Grant says companion cropping makes an important contribution to crop species diversity, which in turn, promotes more productive and profitable winter grain crops.

Illustrating this effect, the Pontifex team found that canola grown as a companion to broad beans, yielded about 300 kilograms per hectare more than where canola was grown as a monoculture during the 2019-20 season.

Nuffield knowledge 

Grant and his family have grown canola and broad beans, chickpeas and linseed, and wheat and lentils as companion crops in the past three years. PHOTO Matt Turner

Grant and his family have grown canola and broad beans, chickpeas and linseed, and wheat and lentils as companion crops in the past three years. PHOTO Matt Turner

This yield gain across 1200ha of ironstone buckshot gravel over sand on Kangaroo Island was consistent with the findings of Grant's 2018 Nuffield scholarship examining farming systems in the United Kingdom, France, United States and Canada.

"A trial in the UK showed a farmer achieved a two tonne per hectare-yield gain in wheat when it was planted as a companion to field peas instead of as a single species crop," Grant says.

In addition to canola and broad beans, the mix of companion crops planted on the family's mainland and island farms over the past three years has comprised chickpeas and linseed, and wheat and lentils. Plus they are trialling linseed and faba beans this season.

The Pontifex team partner a nitrogen-fixing legume with a cereal, oilseed or flaxseed to encourage nutrient and moisture exchange between companion planted species. This approach helps capitalise on the effect in which a legume 'trickle-feeds' nitrogen to its crop companion.

Other important considerations shaping the family's companion cropping program are harvestability and storage.

For example, broad beans and canola can be harvested simultaneously because the disparity in crop seed size can be thrashed effectively through the header rotor sieves.

On-farm experimentation has also shown they can store broad beans and canola together in 200 tonne silo bags.

Grant says there was no moisture transfer between the different grain types in storage, even though these crops have different maximum moisture content requirements: 14 per cent in broad beans and eight per cent in canola.

See also:

More information: Grant Pontifex, 0429 477 800, gjponty@bigpond.com

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