Sub-performing soils in southern research spotlight
GroundCover™ Issue: 125 Nov - Dec | Author: Rebecca Jennings
The GRDC, along with agricultural research organisations, is co-investing in two projects worth nearly $18 million over five years to rectify soil constraints in the southern region
Two major new research initiatives are aimed at providing growers with a guide to how, when and where they can incorporate organic matter and other ameliorants to overcome constraints to root growth, crop yield and profitability arising from poor soil structure.
One project addresses amelioration processes for heavy clay subsoils mainly in medium to high-rainfall zones, while the other focuses on increasing agricultural production on sandy soils in low and medium-rainfall areas.
Although the two projects are separate, both tackle challenges facing growers across the southern region (and into southern NSW) and build on past research into subsoil constraints.
GRDC general manager of systems and agronomy south, Dr Stephen Loss, says tackling soil constraints is an important opportunity for growers: “These two projects will address limitations on the two most widespread and ‘difficult’ soil types – the heavy clays with poorly structured subsoils and sandy soils with limited water-holding capacity.”
to develop cost-effective practices that fundamentally change soil properties to increase root growth and depth, and water and nutrient uptake.
“Some of these practices have only been tested experimentally and are currently cost-prohibitive, and it will be a major challenge for the researchers to develop more affordable amelioration techniques that are practical on a large scale,” he says.
Project 1: Organic matter put to the economic, yield test
Target areas: Medium and high-rainfall zones of South Australia, Victoria, Tasmania and southern NSW
GRDC investment: $4.95 million over five years
Research partners: Agriculture Victoria, South Australian Research and Development Institute (SARDI)/Primary Industries and Regions SA (PIRSA), NSW Department of Primary Industries, La Trobe University, University of SA, Southern Farming Systems, University of Tasmania
Subsoil constraints have been the focus of research in southern farming systems for decades, but soil scientists are now taking knowledge about amelioration strategies a step further to better understand how crop performance can be improved by applying organic matter and other ameliorants to subsoils.
The diverse range of soils in the region – including duplex soils and sodic clays – present constraints in the subsoil, such as sodicity or high boron. These can limit root growth, impede water and nutrient use by crops, and reduce grain yields and profitability.
Strategies such as deep-ripping, applying gypsum or incorporating organic matter at depth have been tested to overcome subsoil constraints. While subsoil manuring has been shown to be effective, the lack of broadacre machinery, potentially high cost of these practices and a lack of access to ameliorants have seen many growers choose to reduce inputs or restrict crop choice rather than chase higher yields through these techniques.
Project leader Roger Armstrong, from Agriculture Victoria, says this new project will build on knowledge produced by earlier projects. These include the SARDI/PIRSA New Horizons work in SA and previous research by La Trobe University and Agriculture Victoria to develop the agronomic practices required to overcome soil constraints, with a focus on reducing financial risk and logistical constraints.
“In previous trials we saw large responses that are possible from subsoil amelioration methods, such as incorporating chicken manure at depth, which delivered up to 80 per cent in yield gain,” Professor Armstrong says. “However, some strategies are costly – for example, subsoil manuring can cost up to $1200 per hectare.”
The project team will seek to answer questions such as:
- How effective are different ameliorants? Can cereal or legume straw do a similar job? What are the minimum rates of application and what is the optimal depth for placement?
- What environments, soil types and rainfall zones are best suited – or not – to incorporating different types of organic matter?
- How can growers overcome logistical challenges, such as the machinery required to apply these ameliorants at the paddock scale?
- How can growers overcome the financial risk of large up-front expenses related to amelioration strategies?
Previous trials will be monitored to assess the long-term residual value of applying organic matter, and new trials will kick off in 2017 across a mix of environments, rainfall zones and soils in four states.
Professor Armstrong says he expects the range of products available to be narrowed down to four or five forms in glasshouse experiments, and then applied in combinations of source, rate and depth of incorporation across the major soil types in the field trials. Gypsum to address sodic subsoils will also be assessed.
These trials will help better understand the chemical, physical and biological soil properties and processes underpinning improvements in crop performance following the incorporation of organic matter and other amendments.
“Our aim is to demonstrate what technologies and strategies will be economically viable in different rainfall environments, to provide growers with information about where it will, and just as importantly won’t, provide a yield benefit,” Professor Armstrong says.
The project will include a scoping study led by Uni SA agricultural engineers to identify machinery requirements for incorporating different organic materials, which could guide the development of future commercial equipment. There will also be an economic analysis component to assess the financial and potential returns over time under a range of seasonal conditions.
GRDC Research Code DAV00149
Project 2: Sights set on sandy soil productivity
Target areas: Low and medium-rainfall zones of SA, southern NSW and Victoria
GRDC investment: $4.5 million over five years
Research partners: CSIRO, PIRSA, University of South Australia, Mallee Sustainable Farming and Ag Grow Agronomy
Sandy soils are a challenge for many growers in the southern cropping region, especially those who are frustrated by poor crop performance in paddocks that have residual subsoil water after the crop is harvested.
Therese McBeath of CSIRO Agriculture, who is leading this GRDC-funded project, says an estimated five million hectares of under-performing sandy soils in the southern region could present an untapped resource.
“There has been significant work into sandy soils in recent years, and research has been separated into mitigation strategies, which are low-cost annual interventions that typically have a small impact on yield, and high-cost, high-impact and long-term amelioration treatments,” she says.
“This project aims to bring all these intervention strategies together, so when a grower is approaching a sandy soil on their farm they can think about all the options available, to decide what strategy is best from a financial and productivity perspective.”
The project will look at the spectrum of crop constraints and interventions across different types of sand and environments at eight sites in SA, Victoria and southern NSW. Unlike the subsoil amelioration project, the focus of this project will be on soils where crop roots are constrained within the sandy layer – not by constraints in the clay or carbonate subsoil layers.
Mitigation treatments will include nutrition strategies, using soil wetters and seeder set-ups, while the amelioration work will encompass trials established under the SARDI/PIRSA New Horizons Program, along with new experimental sites to assess interventions such as soil inversion or disturbance and incorporation of clay, organic matter and nutrients.
While the New Horizons work took a ‘what if’ approach to test the upper limits of interventions, this new project will home in on strategies that offer growers a commercially viable option and will also carefully consider the production and financial risk of an intervention.
“The aim is to develop appropriate and cost-effective management strategies with high returns and low risk so growers can better match the yield attained with their yield potential,” Dr McBeath says.
The research team recently held regional engagement meetings to capture grower perspectives on sandy soil issues, the successes and failures of any interventions tested, and the economic context for the selection of mitigation versus amelioration interventions.
Dr McBeath says recurring comments from growers included the need to consider the response of the whole farming system to the intervention, for example, knowing how to manage a paddock after an expensive amelioration strategy to best capture benefits from the investment in subsequent years.
GRDC Research Code CSP00203
More information:Lynne Macdonald (project leader from November 2016),
GRDC Project Code DAV00149, CSP00203
Region North, South