Conservation farming -No-till pioneers celebrate a $500m legacy

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Emma Leonard reflects on 30 years of remarkable R&D emanating from the Avon trials site in South Australia, where much of today's no-till and conservation farming systems were developed

When Avon growers Robin and Olive Manley were asked by Dr Albert Rovira, then of CSIRO, if they could provide some land for a three or possibly six-year trial, they were happy to oblige. That was in 1976. Little could the couple have realised that it would be 30 years before the trial program would finally wind up, and by then be cemented into history as one of the most remarkable sources of knowledge on Australian dryland cropping.

It has been the site where many of the principles of no-till under Australian conditions were established and where, by the trial's closure in 2006, new conservation farming practices had been given a strong start.

Researcher Dr David Roget, who joined the project in 1979 and managed it for the next 22 years, said the site was chosen because it provided soil, rainfall and climate typical of the Mallee but within easy reach of Adelaide.

The original project was looking at the impact of root disease on cereal yield and the Avon site was low in cereal cyst nematode and similar to soils that had shown large yield responses to fumigation trials.

In the 1970s and early 1980s, most growers in this region followed a cereal/grass-medic pasture rotation. The trial experimented with five rotations:

  • continuous wheat;
  • grassy pasture/wheat;
  • sown medic pasture/wheat;
  • peas/wheat; and
  • oats/wheat

The researchers were looking for the effect of rotation on cereal root disease, especially the fungus take-all. At the same time, the new concept of direct-drilling crops using a non-residual herbicide (Sprayseed®) instead of ploughing was measured against conventional cultivation.

The first significant observations were that take-all levels and yield varied substantially with rotation and method of sowing. Take-all peaked at 60 per cent incidence when wheat followed a grassy medic pasture (one tonne per hectare yield) or when wheat followed wheat and was direct-drilled, but fell to about 10 per cent when wheat followed peas or sown medic and was sown conventionally (two to 2.5t/ha).

[Photo (left) by Emma Leonard: (From left to right) Robin Manley, Dr David Roget and Dr Albert Rovira: 30 years of research at Avon produced many of the principles that now underpin no-till, conservation farming practices in the low-rainfall regions.]

These results showed that rotations with crops or pastures that did not host take-all were necessary to maximise the use of rainfall. They also helped to explain why the graze-spray techniques being promoted for direct-drilling were not working in SA, because farmers generally had grassy medic pastures and therefore high levels of take-all.

So, if take-all was influenced by rotation why were the direct-drilled crops not performing as well as those sown by conventional cultivation?

Booboorowie grower Jack McMahon (left) and Albert Rovira reminisce about the development of narrow points, one of the major outcomes of the Avon trials[Photo (left) by Emma Leonard: Booboorowie grower Jack McMahon (left) and Albert Rovira reminisce about the development of narrow points, one of the major outcomes of the Avon trials.]

The scientists realised they must be dealing with more than one root disease and eventually established that Rhizoctonia solani was also pruning roots and limiting crop growth.

What they did not know was that direct-drilling actually favoured Rhizoctonia, due to more of the fungal hyphae being left intact in the soil; plus, the fungus was not greatly affected by rotation.

A young Albert Rovira during his pioneering research into the early soil biology problems that threatened to thwart the introduction of minimum till[Photo (left): A young Albert Rovira during his pioneering research into the early soil biology problems that threatened to thwart the introduction of minimum till.]

Before the introduction of direct-drilling, Rhizoctonia had not been seen at Avon, but within two years of direct-drilling being tested, up to 46 per cent of the wheat sown by this method, either after a grassy pasture or wheat, was lost to Rhizoctonia.

At this stage, Dr Stephen Neate switched his attention from take-all to Rhizoctonia and established that the 'Sirodrill', developed by the research team for direct-drilling, was not disturbing the soil enough to break up the stands of fungus in the top five centimetres of soil. At the same time, the drill was placing the seed where there was the greatest Rhizoctonia density.

In the spring of 1985, Dr Rovira presented the issues relating to Rhizoctonia at a field day, and on the whiteboard drew the sowing point he thought was needed to overcome the problem of Rhizoctonia with direct-drilling.

"A few months later," recalled Dr Rovira, "Booboorowie grower Jack McMahon walked into my office with a McKay Lucerne point which had a five-centimetre-long steel blade welded to the bottom - and so began our work with narrow sowing points."

The introduction of narrow points made it relatively inexpensive for farmers to switch to direct-drill seeding, and the addition of tungsten tips - another innovation emanating from Avon - meant the points lasted more than one paddock in the abrasive soils.

David Roget and Neil Venn are credited with the other part of the now-common practice for Rhizoctonia control: chemically removing the 'green bridge'. Shortly after an April rainfall event, they decided to spray-out strips of volunteer plants across the trial plots. To everyone's surprise, less Rhizoctonia occurred in the strips that had been sprayed. This chemical fallow, three weeks before seeding, removed the green bridge and reduced take-all and Rhizoctonia damage in the following cereal crop.

David Roget had already identified a clear link between spring rainfall one year and the level of take-all in the following year. Indeed, this finding, together with work by Dr Gupta Vadakattu on the influence of soil moisture and temperature on take-all, provided the basis for the take-all prediction now used by the root disease testing service.

But no such link with rainfall was found with Rhizoctonia. Indeed, the occurrence of the two root diseases showed completely different patterns. Despite the new advances of chemical fallow and narrow points, Rhizoctonia was not completely controlled in direct-drilled crops. Instead, it steadily increased for the first four years, and then fell away to no further disease after 10 years in all rotations and both tillage systems.

Take-all occurrence varied much more with seasonal conditions, but after eight years of rotations a decline to negligible levels was also recorded. It was eventually determined that the reason for the decline in both diseases was the development of a natural biological suppression linked to an increase in carbon input: that is, stubble retention.

"It was the long-term nature of these trials that allowed us to unravel these complex biological reactions," David Roget says.

Another important and unexpected result from the Avon long-term trials was the finding that intensive cereal systems with stubble retention resulted in an average annual input to the soil of 20 kilograms of nitrogen per hectare. This free nitrogen was found to be the contribution of free-living nitrogen-fixing bacteria, which built up on the decomposing plant residues.

At a lunch celebrating the achievements from Avon and the closure of the trial site, Albert Rovira and David Roget both emphasised the important role that growers had played in their research. They also highlighted the role of long-term support from the GRDC, the former Wheat Research Fund and CSIRO.

"And if we take outcomes from the Mallee Sustainable Farming project alone, we estimate that the benefits of modifying and adopting the research findings from the Avon site amount to about $500 million each year in increased grain production and reduced wind erosion," Dr Rovira said. "That is a pretty good return on investment."

GRDC Research Code CSO00028

More information: Mallee Sustainable Farming Inc, www.msfp.org.au; Fields of Discovery: Australia's CSIRO by Brad Collis, (Allen & Unwin), pp236-240

Region North, South, West