Trials dig deep to ameliorate sodic soils
GroundCover™ Issue: 130 September-October 2017 | Author: Nicole Baxter
Researchers are investigating the effectiveness of surface and deep placement of amendments to ameliorate subsoil constraints
The start of every season is a busy time for grain growers and equally so for researchers in their efforts to establish trials quickly and accurately to reflect industry best practice.
Among this activity in 2017 were NSW Department of Primary Industries researchers from the Wagga Wagga Agricultural Institute, who, with GRDC investment, have established a trial to examine the effectiveness of surface and subsurface application of different organic and inorganic amendments on sodic soil at Rand, 100 kilometres south-east of Wagga Wagga.
Sodic soils are high in sodium and prone to dispersion and low water infiltration. As a consequence, they often suffer from temporary waterlogging, runoff and gully erosion. They are also susceptible to surface crusting, which can hinder seedling emergence.
Crops grown on sodic soils frequently suffer from poor root growth due to high soil strength and alkalinity, especially in the subsoil, and limited availability of water and nutrients. These physical and chemical soil properties reduce overall crop growth and grain yield.
To understand how subsoil application of amendments affects these soil constraints, the GRDC has invested in a five-year multi-agency team of researchers from Victoria, Tasmania, South Australia and southern NSW led by Agriculture Victoria’s Dr Roger Armstrong. Spearheading the research in southern NSW is NSW DPI soil scientist and crop physiologist Dr Ehsan Tavakkoli based at Wagga Wagga.
The agencies contributing to the GRDC sodic soils research group (DAV00149) are:
- Agriculture Victoria (Roger Armstrong (project leader))
- NSW Department of Primary Industries (Ehsan Tavakkoli (NSW leader))
- La Trobe University (Peter Sale)
- South Australian Research and Development Institute (Nigel Wilhelm and David Davenport)
- Tasmanian Institute of Agriculture (Geoff Dean)
- University of South Australia (Jack Desbiolles)
- Southern Farming Systems (John Midwood)
- University of Melbourne (Bill Malcolm)
In 2016, NSW DPI technical staff designed and custom-built a deep-ripping machine for a GRDC-supported project, ‘Investigating innovative technology to ameliorate subsoil acidity’.
In 2017 the machine is being tested in the field to evaluate its effectiveness in delivering soil amendments at dual depths where subsoil sodicity and dispersion are issues.
At the Rand site, soil pH (calcium chloride) ranged from 5.1 to 8.2 with increasing sodicity at depth (exchangeable sodium measuring up to 30 per cent) (Figure 1).
Dr Tavakkoli says any soil in Australia with an exchangeable sodium percentage of more than six per cent is considered ‘sodic’.
“More than 60 per cent of the 20 million hectares of soils used for cropping in Australia are sodic,” he says. “On a world scale, Australia has by far the most extensive distribution of sodic soils.”
Additionally, Dr Tavakkoli says after harvest in 2016 at the Rand site, large amounts of soil water were found below 60 centimetres, which was potentially available to the crop, but had remained unused, suggesting the crop’s roots were prevented from accessing this subsoil water.
“Previous research suggests that each millimetre of this subsoil water has the potential to produce 25 kilograms of grain/ha,” he says.
“Enabling crops to fully utilise this subsoil water will underpin improved productivity and potentially create a step change in profitability.”
When dispersion occurs, he says clay particles fill up the pores between the soil particles and aggregates.
As the soil dries the dispersed clay blocks the soil pores, restricting seedling emergence, water and air movement and crop root penetration.
This year at Rand the researchers are testing 15 different amendment combinations to determine the most useful method to improve yields over the next four seasons.
“Next year we will focus on examining fewer amendments but in more detail, while continuing to monitor changes to the soil’s chemical, physical and biological properties treated in 2017 and the effects on grain yield, quality and profit over time,” Dr Tavakkoli says.
“If our trials point to a way to cost-effectively ameliorate sodic soils, the technology may be commercialised, potentially offering growers a pathway to much improved financial returns.”
The Rand site is also part of an associated national multi-agency GRDC investment led by Associate Professor Glenn McDonald, from the University of Adelaide, across 11 Australian sites to screen bread and durum wheats for tolerance to sodic and dispersive soils.
Dr Tavakkoli says early results from Rand show wheats differ in their tolerance to sodic and dispersive soils. This initial analysis suggests that the benefit from improved tolerance to constraints found in sodic soils will be greatest at sites where yields are less than about 3.0 to 3.5 tonnes per hectare.
Going forward, Dr Tavakkoli says the national research team will continue to screen wheat lines using in-paddock and greenhouse experiments.
“Our findings will be combined with those from South Australia, Victoria, Queensland and Western Australia to identify suitable parental lines for future variety development,” he explains. “We hope this work will lead to the release of commercial wheats that combine tolerance to the major stresses encountered in sodic and dispersive soils including salinity, boron toxicity, aluminium toxicity and waterlogging.”
GRDC Research Codes DAV00149 and UA00159
0421 018 075,
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