Former CSIRO scientist and microbiologist Dr Margaret Roper says her research shows current soil amelioration cultivation practices are harming the soil microbial population responsible for building fertile soils.

Former CSIRO scientist and microbiologist Dr Margaret Roper says her research shows current soil amelioration cultivation practices are harming the soil microbial population responsible for building fertile soils.

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

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

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

By KEN WILSON
THERE are no magic bullets.
You have probably heard that ad nauseum in agriculture while encountering such problems as chemical resistance, low soil pH, plant diseases, et al.
As far as you’re concerned it’s a truism, based on self evidence.
But things are changing to a point where CSIRO and GRDC scientists and researchers are pointing to neglected ‘magic bullets’ that exist literally under your feet.
You know them as bacteria, fungi and small soil animals, otherwise referred to as soil microorganisms or soil microbes, which basically are the building blocks of fertile soil.
There are between one and two tonnes a hectare of microbes in the top soil with 70 per cent in the top 10 centimetres, providing more than 10 billion microbes in a kilogram of soil with literally kilometres of fungal hyphae.
The hyphae spreads like a network to capture nutrients and in a highly complex symbiotic relationship, provides these nutrients to plant roots while accessing food in the form of exudates from the roots.
A classic visual of this process is the ‘dreadlock’ roots you find on healthy plants.
What science is now showing, through trial research, is a better way to grow crops - better than what might be regarded as the game-changer for broadacre farming in the 1990s when no-till became the norm.
And better than the evolution from deep ripping (dating back to the late 1960s) to wholesale soil amelioration techniques which has seen ‘rediscoveries’ of the mouldboard plough and the one-way plough.
Today’s focus is on eliminating non-wetting soils, where possible to invert and bury weed seeds (mouldboarding) and mixing lime, clay and gypsum to elevate soil pH (at least in the top 10-20cm of the soil) and to create more water-holding capacity, through an improvement in soil structure.
Ironically, these cultivation solutions, which have given economic responses and on face value appear to be sensible management practices, also promote problems, ie, chiefly, upsetting or destroying fungal hyphae networks.
There is conjecture 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, that cultivation practices can reduce organic matter and water-holding capacity in WA’s 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 2008, Dr Roper was involved in a trial program at Munglinup and after four years of measuring organic matter in ‘district practice’ plots (cultivation and stubble burning), a noticeable depletion in organic matter levels occurred in the top soil down to 10cm, 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.”
According to Dr Roper, there is world research 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.
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 Dr Roper points to trials involving near-row sowing in South Australia and WA which have shown promise.
“At this stage it remains a hypothesis because of the lack of long term trial data,” Dr Roper said. “But initial work I have been involved with for more than a decade does point to a range of benefits.
“Near-row sowing implies establishing crops close to the previous year’s crop rows where there is a high likelihood of moisture, which new roots gravitate towards and establish in old root pathways.
‘It is in this environment, where moisture is present, that beneficial soil microbes populate, including wax-degrading bacteria (eliminating non-wetting).
“And compared to the non-wetting inter-row, the microbial population is far greater than that in the inter-row by a factor of 10.”
It follows that a soil that hasn’t been dried out by cultivation, has the potential to build carbon levels to create more water-holding capacity and increase soil fertility leading to healthier crop plants with high yield potential.
The obvious question is how sustainable is planting in virtually the same row year after year, which can induce plant root diseases.
According to Dr Roper the sheer population of beneficial microbes can play a positive role in suppressing diseases, with trials already showing suppression of crown root rot in cereals.
And the bonus of maintaining the same planting rows, creates a hostile, dry (from non-wetting) inter-row where weeds will struggle to grow.
Additionally, with growing soil fertility implying structured soil, there may be no need for the costly type of deep ripping, spading or mouldboarding.
“I believe near-row crop establishment is the closest thing yet to sustainability,” Dr Roper said.
And she believes there is more to come from research efforts, particularly related to in-furrow liquid nutrient applications.
Currently Dr Roper is working with Ausplow Farming Systems on a trial program at Quairading specifically assessing the attributes of in-furrow liquid nutrient applications.
“We could be on the cusp of something really exciting but it is still early days,” she said.
(Published in Farm Weekly, September 3, 2020 and used with kind permission).

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Publish Date: 
Friday, September 18, 2020