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Cultivation the bogeyman of crop establishment

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Cranbrook farmer Theo Cunningham (left) digs into an old root pathway to examine subsoil. He is being watched by Ausplow research and development coordinator Dr Margaret Roper and Ausplow managing director John Ryan AM.

Cranbrook farmer Theo Cunningham (left) digs into an old root pathway to examine subsoil. He is being watched by Ausplow research and development coordinator Dr Margaret Roper and Ausplow managing director John Ryan AM.

Stubble removed and cultivated prior to seeding. The dye shows the pathways for water movement have been destroyed. Photo courtesy Margaret Roper and Phil Ward, CSIRO.

Stubble removed and cultivated prior to seeding. The dye shows the pathways for water movement have been destroyed. Photo courtesy Margaret Roper and Phil Ward, CSIRO.

Blue dye shows infiltration down new and old rows in a zero-tilled row. Photo courtesy Margaret Roper and Phil Ward, CSIRO.

Blue dye shows infiltration down new and old rows in a zero-tilled row. Photo courtesy Margaret Roper and Phil Ward, CSIRO.

Former CSIRO scientist and microbiologist Dr Margaret Roper … cultivation can reduce organic matter and water-holding capacity in the soil.

Former CSIRO scientist and microbiologist Dr Margaret Roper … cultivation can reduce organic matter and water-holding capacity in the soil.

By KEN WILSON
THERE is no denying that agriculture has experienced a series of paradigm shifts over the past 70 years.
And as technology wraps itself tightly around the industry, more attention is being paid to technological changes such as variable rate product applications, robotic farming, et al.
Technology also has been employed in the form of mouldboard ploughs, spaders and deep rippers to ameliorate WA’s soil water repellency and bury weed seeds - practices we have seen ramped up over the past decade.
But for all that focus, aimed at producing higher-yielding crops (and in some cases pastures), there remains a missing piece to the jigsaw puzzle that is farming.
The missing piece is often referred to but it remains out of sight and mostly, out of mind.
I’m of course referring to bacteria, fungi and small soil animals, otherwise referred to as soil microorganisms or soil microbes. Soil microorganisms are many and diverse and it is estimated there are more than 10 billion microbes in a kilogram of soil.
Soil microbes process organic materials of plant and animal origin into soil organic matter and contribute to soil structure.
They decompose pollutants, are responsible for biological control (including controlling plant diseases), and cycle nutrients in the soil for plant and microbial use.
Soil organic matter significantly increases the water-holding capacity of soils, particularly sandy soils.
There is conjecture, however, about how soil microbes and organic matter are affected by technology but former CSIRO scientist and microbiologist Dr Margaret Roper is in no doubt, on the back of more than a decade of trials: cultivation practices can reduce organic matter and water-holding capacity in our water-repellent sandy soils.
“We have consistently found in trials over the years that cultivation (and stubble burning) will result in the loss of organic matter in the soil,” Dr Roper said.
In the 1980s ‘district practice’ was to burn stubbles before cultivating and seeding, but after a series of severe wind erosion events, no-till with stubble retention was gradually adopted.
In 2008, Dr Roper was involved in a trial program at Munglinup and after four years of measuring organic matter in ‘district practice’ plots, a noticeable depletion in organic matter levels occurred in the top soil down to ten centimetres, compared with no-till plots.
“It happened quite quickly from 2009 onwards,” Dr Roper said. “It was so consistent that we stopped the burning in 2011 but we retained the plots in our overall trial program.
“From 2012 to 2017 we returned all plots to no-till and stubble retention.
“After six years, the plots that were previously burned and cultivated in the first four years of the trial, showed little or no recovery in terms of organic matter levels, water-holding capacity and crop yields when compared with the plots which had been under no-till and stubble-retention from the beginning of the trial.
“It can really take a long time for the soil to recover from burning stubbles.”
Interestingly when the Munglinup trials started, the soil water content was always higher in the more repellent no-till and stubble retained plots than the cultivated and burned plots.
“In the cultivated and burnt treatment, with least repellence water infiltration was less,” Dr Roper said.
“This went against conventional thinking because the more soil organic matter the more waxes are present to make soil more water-repellent.
“Waxes are produced by plants to protect them from loss of water. When plant material decays, waxes are released and coat sand particles and cause repellency.”
The research team of Dr Roper and colleagues Phil Ward, Ramona Kerr and Shayne Micin, discovered, through dye tests, that no-till had preserved the old plant root pathways which allowed water to travel beyond the water-repellent top layer of the root zone.
“It was easy to see in the cultivated and burnt plots that the dye couldn’t penetrate with root pathways destroyed,” Dr Roper said.
Dr Roper and her team continued research into water repellence - and diseases - and in 2011 organised trials involving on-row and inter-row crop establishment in a no-till stubble retention system.
“We had similar results with crops sown into the row and moisture infiltrating old root pathways,” Dr Roper said. “On the inter-row, it was bone dry, even after significant rain.”
This research work has set up the tantalising prospect of establishing crops every year near the previous year’s plant rows (near-row sowing) to continue to build organic matter and create, eventually, paddocks with the capacity to hold water in the topsoil.
Such an effect would mean the proliferation of beneficial bacteria and a healthy soil environment to enhance soil structure and microbial functions.
According to Dr Roper, there is research around the world that shows if you create an environment that increases organic matter, you can achieve a significant increase in available water-holding capacity, and this can be more pronounced in sandier soils.
The problem is getting to that level of soil fertility. It’s not a quick fix.
Having said that, Dr Roper says the trial results at Munglinup showed that improvements in water infiltration are rapid (less than three years) after transitioning from cultivation to no-till due to early development and preservation of new root pathways for water flow, that by-passes repellent surface soil layers.
Conversely, rebuilding soil organic matter and associated water-holding capacity after transitioning from stubble burning to stubble retention, is much slower (greater than six years) and so is the accumulation of crop residue ground cover that protects soils from temperature extremes and conserves soil water.
Understanding how long it takes to restore soil to its optimum fertility remains elusive.
And in an economic environment where every paddock must make money, it’s problematic that any paradigm shift, alluded to here, will occur, particularly with farmers cropping in sandy soils.
But while soil amelioration techniques maybe working, it could be argued that the cost of these techniques warrants a closer look at the cheaper technique of near-row sowing.
Naysayers will quickly point out the disease build-up associated with such a method, but Dr Roper says there is no evidence of diseases associated with the Munglinup trials.
“It (disease) certainly needs a proper evaluation but our trials show, in the presence of moisture in the old root pathways, beneficial bacteria can flourish. Some of these bacteria have the potential to reduce root diseases.
Whether the Munglinup trials will gain broader traction with farmers remains to be seen.
But if the goal is to produce more from existing land holdings, it is arguable that maintaining methods that preserve organic matter and soil structure, are the right way to go.
(Story courtesy FARM WEEKLY).

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Saturday, January 18, 2020