Holistic approach to farm management promotes soil health in SA

On-farm strategy combines soil health-sensitive tactics across three SA family farms

Agronomy
South Australian grower Grant Pontifex draws on his 2018 Nuffield scholarship exploring farming systems around the world to promote healthier soils on farms at Paskeville and on Kangaroo Island. PHOTO Matt Turner

South Australian grower Grant Pontifex draws on his 2018 Nuffield scholarship exploring farming systems around the world to promote healthier soils on farms at Paskeville and on Kangaroo Island. PHOTO Matt Turner

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The Pontifex family combines ground cover cropping and organic fertiliser applications.

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SNAPSHOT

  • Owners: Grant and Jodie, Ben and Sarah Pontifex
  • Location: Paskeville; American River and Vivonne Bay (Kangaroo Island), South Australia
  • Area: 7000 hectares; 2400ha at Paskeville, 2300ha at American River, 2300ha at Vivonne Bay
  • Soil types: Red clay loam at Paskeville; ironstone buckshot gravel over sand on Kangaroo Island
  • Soil pH: 8 at Paskeville, 4.5 to 6 on Kangaroo Island
  • Average annual rainfall: 400 millimetres at Paskeville, 550mm at American River, 650mm at Vivonne Bay
  • Cropping: hard wheat, feed barley, lentils, chickpeas, faba beans at Paskeville; broad beans, soft wheat, malting barley, canola and linseed on Kangaroo Island

A holistic approach to farming systems management targeting soil health has seen the Pontifex family improve the vitality and sustainability of their grains operation on 7000 hectares spread across three properties straddling Adelaide, South Australia.

Connecting the dots between the locations of these properties, the satellite view plots a thin wedge reaching across the SA coast, south-west and north-west of the state's capital.

Two properties are anchored in the Great Australian Bight on Kangaroo Island at American River and Vivonne Bay, while a third property, the original family farm, is located on the mainland at Paskeville on the Yorke Peninsula.

At first glance, the farms on Kangaroo Island and at Paskeville, separated by 330 kilometres including a small stretch of sea, might appear to have little in common.

There is a disconnect between the rainfall, soil type and acidity, climate and operational logistics of these far-flung farms.

FARMING SYSTEMS LINK

A closer look, however, reveals the three farms are intrinsically linked by the Pontifex family's big-picture vision for a more resilient and sustainable farm business, which draws on a range of cultural practices to improve biological soil health, particularly soil organic carbon.

Achieving this vision is a long-term push for the Pontifex team, including Grant and Jodie who run 2400ha at Paskeville, and Ben and Sarah who run 2300ha at American River and 2300ha at Vivonne Bay.

The team's integrated strategy comprises ground cover and companion cropping, organic fertiliser applications and zero-till practices with an emphasis on crop residue retention.

Of this "long-term investment", Grant estimates that, to date, the combination of tactics to promote healthier soils has lifted soil organic carbon from 1.5 to 2 per cent (soil organic matter), and increased crop water-use efficiency from 12 to 18 kilograms per millimetre.

Much of this improvement stems from the organic fertiliser program implemented at Paskeville in 2005, Grants says. (An equivalent program was not established on the Kangaroo Island farms due to the prohibitive freight cost of manuring).

ORGANIC FERTILISER   

Grant has implemented a chicken manuring program across 2400 hectares of the original family farm at Paskeville on South Australia's Yorke Peninsula. PHOTO Matt Turner

Grant has implemented a chicken manuring program across 2400 hectares of the original family farm at Paskeville on South Australia's Yorke Peninsula. PHOTO Matt Turner

The organic fertiliser program, ongoing for 15 years on the Yorke Peninsula, sees chicken manure annually spread on the soil surface across 2400ha at a rate of 2.5 tonnes per hectare during April.

This approach delivers a slow-release supply of major and minor nutrients to crops that enabled the family to eliminate starter phosphorus fertiliser and trace element inputs from its synthetic fertiliser program within a five-year period, Grant says.

He says previous expenditure on synthetic phosphorus and trace element inputs was about $70 per hectare or $168,000 a year over the total Paskeville farm area.

"Chicken manure provides most of our crop nitrogen needs as well," Grant says, adding that the cost saving on synthetic nitrogen fertiliser is estimated at $50/ha or $120,000 per year.

"In the past few years, for example, we have not had to apply any additional nitrogen fertiliser due to the low rainfall in dry seasons. But we do apply nitrogen in high-rainfall seasons when there is more yield potential."

Together, these reduced synthetic fertiliser costs, totalling $288,000 a year, see the family recoup its expenditure on manuring operations. The cost of manuring at Paskeville, including purchase, freight and spreading, is about $80/ha or $192,000 a year, he says.

FARM BUSINESS LIFT

The manuring also adds incrementally to the farm business bottom line through boosting the overall fertility of their loamy red clay soils which, in turn, promotes more productive and profitable wheat, barley, lentil, chickpea and faba bean crops.

Grant says these soil amelioration benefits range from better nutrient cycling and microbial activity to enhanced soil drainage and aeration, and increased moisture infiltration and conservation.

The Pontifex team spread the organic amendment on the soil surface to preserve the effects of zero-till management as part of their integrated strategy to improve soil structure and functionality.

"Spreading manure on the soil surface means we lose about 50 per cent of the nitrogen it contains to volatilisation," Grant says.

"But the benefit of moisture retention with zero-till is more important than the nitrogen loss in our low-rainfall farming system."

In an effort to reduce volatilised nitrogen losses, chicken manure is applied in cool conditions or when rain is forecast, plus it is spread on the soil surface of cover cropping country.

"Spreading manure into our cover crops helps retain 20 to 25 per cent more nitrogen, which is captured in that living crop," Grant says.

COVER CROPPING 

Grant, left, Ben and his daughter Quin, and Neil Pontifex are committed to the family's long-term investment in soil health. PHOTO Pontifex family

Grant, left, Ben and his daughter Quin, and Neil Pontifex are committed to the family's long-term investment in soil health. PHOTO Pontifex family

The family's multi-layered strategy geared to lift soil health and vitality on all three SA farms is also underpinned by an experimental cover cropping program.

The program's design was informed by Grant's 2018 Nuffield scholarship exploring cover cropping and manuring in farming systems across the United Kingdom, France, United States and Canada.

"I looked at cover cropping around the world, mostly in high-rainfall environments where there is more opportunity to grow crops throughout the year," Grant says.

"We receive limited rainfall for growing cover crops during summer on our properties which is quite a challenge.

"However, the principles of cover cropping observed in high-rainfall farming systems in other countries are interchangeable with our low-rainfall environment; the benefits are just expected to take longer to emerge."

CLIMATIC CHALLENGE

Rising to this climatic challenge, the Pontifex team have sown cover crops, comprising a mix of nine different crop species, during summer following their winter cash crops for the past four years.

In 2020, for example, the family planted a cover cropping cocktail of millet, lablab, canola, sorghum, sunflowers, mungbeans, maize, linseed and safflower on 700ha.

Only 100ha was planted on the Paskeville property because this mainland farm receives relatively low annual rainfall, averaging 400 millimetres.

They planted 600ha on their Kangaroo Island properties this summer growing season because these farms receive more annual rainfall, averaging 550 to 650mm. Cover cropping is also part of a strategy to remediate soils affected by the bushfires that burnt almost half of Kangaroo Island in late December 2019.

Of this "fire-recovery strategy", Grant says the cover crop planted this year helped secure the soil surface on fire-affected paddocks vulnerable to erosion.

For instance, cover crops averted topsoil drift across 600ha of burnt country when about 50mm of rain fell on Kangaroo Island during summer.

It is beneath the soil surface, however, extending throughout the entire soil profile, that cover cropping provides a suite of holistic biological benefits for the farm business.

Grant says the program aims to stimulate soil biology throughout the year, in both winter and summer growing seasons, while promoting soil organic carbon capture, nutrient cycling and water-holding capacity.

SPECIES DIVERSITY

Grant and his family sow cover crops, containing a mix of nine different crop species, during summer following their winter cash crops, such as canola. PHOTO Pontifex family

Grant and his family sow cover crops, containing a mix of nine different crop species, during summer following their winter cash crops, such as canola. PHOTO Pontifex family

Helping to promote these benefits, particularly in terms of soil biota, is the diversity of plant species contained in the cover cropping blend of warm season grass and broadleaf crop types.

"The more crop diversity the better. Some growers in the US, for example, combine up to 25 different plant species in cover crops," Grant says.

He says each plant species makes a different contribution to overall soil health. For instance, sunflowers have a taproot that breaks open the soil at depth, while millet has a fibrous root system that infiltrates small soil pore spaces.

However, an experimental approach to cover cropping means the family's formula for diversity is continuously fine-tuned to identify crop species suited to SA growing conditions.

For example, they are considering eliminating legumes and tillage radish from the species mix, since these crop types provide insufficient plant residue and have high moisture requirements respectively.

They also started growing perennial kikuyu as a cover crop across 160ha of 'deep, gutless sands" on Kangaroo Island three years ago.

Its dormancy during the winter growing season has allowed them to sow broad beans into this cover crop, and the mat-forming grass has saved on seed and operational costs because it does not have to be sown annually, he says.

The Pontifex team plant cover crops following winter grain harvest, between early December and mid-February. "We do not have any residual soil moisture straight after harvest so we wait for rain or a promising forecast to sow our cover crops," Grant says.

He says expenditure on the program is $40 to $60/ha, based on seed costs of $20 to $40/ha, and operation costs (using their own machinery) of $20/ha.

LONG-TERM INVESTMENT

But Grant emphasises that cover cropping is a "long-term investment" in soil health, the measurable benefits of which are cumulative and can be slow to emerge.

He says these benefits also need to be weighed against the yield penalty that can result from the program.

The Pontifex family have found cover cropping reduces yield in the following winter cash crop by about 10 per cent.

To help minimise losses, cover crops are sprayed out when the first of the plant species begins to flower. This practice terminates grain fill and helps conserve soil moisture for the subsequent winter crop.

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

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