Push to lift sandy soils potential

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The GRDC is investing $9 million into research aimed at developing strategies for overcoming two particular soil constraints in the southern region – water-limited sandy soils and poorly structured subsoil

CSIRO senior research scientist Dr Lynne Macdonald delves into sandy soils as part of a new five-year project to overcome production constraints.

PHOTO: CSIRO

The poor capacity of sandy soils to retain moisture and nutrients – which has long been a frustration for growers in south-eastern Australia – is the focus of a $4.5 million research project to run until 2021.

Leading the GRDC investment project, CSIRO senior research scientist Dr Lynne Macdonald says the research is a collaborative effort between CSIRO Agriculture and Food, the University of South Australia and Primary Industries and Regions SA (PIRSA).

Together with Mallee Sustainable Farming and Ag Grow Agronomy & Research, the team aims to identify cost-effective strategies for improving grains productivity and profitability on deep sands that limit crop root depth and water uptake.

“Opportunities for increasing crop productivity exist on these soils because crop yields appear to be below their water-limited potential and there is unused water in the soil profile at harvest,” Dr Macdonald says.

In the first stage of the project, researchers engaged in 30 paddock-based discussions with growers to gain their perspectives on sandy soil constraints and on-farm management experiences.

Dr Macdonald says these on-farm meetings highlighted three main issues that are high on growers’ agenda:

  • the need to improve nutrient supply and biological fertility in sandy soils;
  • concerns about herbicide impact in the soil; and
  • concerns about erosion as a consequence of deep cultivation, deep ripping and spading.

Such insights, plus analysis of gaps in the research drawing on peer-reviewed science and existing trial data, were used to identify the project’s key areas.

“These constraints to crop rooting depth and water extraction include physical and chemical factors, nutrient supply and biological cycling, and crop establishment on water-repellent soils,” Dr Macdonald says.

However, she says the causes of low crop water use in sandy soils can be difficult to diagnose and manage because there is rarely a single cause.

This means researchers need to quantify the contribution that individual soil constraints make to crop water use in order to assess the underlying causes and their effects.

To this end, researchers are continuing to monitor three PIRSA trials established at Karoonda, Cadgee and Brimpton Lake in SA in 2014 to help better understand the long-term benefits of adding clay and organic matter to the soil.

This year, they also established new long-term trials at Ouyen in Victoria, Lameroo in SA and Yenda in New South Wales.

Dr Macdonald says the southern NSW trial is examining the potential for deep cultivation with applications of chicken litter and/or lime to overcome physical and chemical soil constraints.

“While chicken litter is known to provide crop growth benefits, there is scope to optimise its use through better understanding application rates and frequency.

Increasing production

Key research areas for increasing production on sandy soils in the low to medium-rainfall areas of the southern region are:

  • identification of poorly performing sandy soils and their issues;
  • physical impediments to crop root growth and water extraction;
  • chemical impediments to crop root growth and water extraction
  • nutrient supply and biological cycling in the rooting zone; and
  • crop establishment and water-repellent soils.
  • “Chicken litter is readily available in parts of SA, such as the Yorke Peninsula and Mallee regions, and NSW, but where chicken litter is not available we need to identify other types of organic matter that can provide benefits over multiple seasons.

    “We are also working to determine how long the benefits of deep cultivation with amendments might last in terms of nutrition, and the biological, chemical and physical effects on the soil.”

    Investigating alternative sources of organic matter, the Victorian trial is examining the scope for crops grown on-farm, such as cereals and vetch, to provide a ‘homegrown’ supply of organic matter.

    “We estimate that six tonnes per hectare of organic matter could be generated on-farm by crops on higher-performing soil types and transferred to underperforming sands,” Dr Macdonald says.

    This trial is testing spading using one pass of a machine set up for both spading and seeding in terms of rapid crop establishment and erosion risk on coarse textured sands.

    Another trial at the Victorian site is looking at optimal placement of nitrogen and nutrient packages (containing phosphorus, zinc, copper, manganese, potassium and sulfur) in the sandy soil profile.

    “The depth of nutrient placement at 40 or 25 centimetres in the soil has implications for which machinery set-up should be used, application frequency and, ultimately, the cost-effectiveness of different options.”

    A third SA trial is assessing different approaches to seed placement, liquid application technologies, and deep-banding organic matter, clay and charcoal to help lift seedbed fertility.

    In the next phase of the project, researchers plan to establish three more trials in SA’s Mallee region, the Eyre Peninsula and the Yorke Peninsula in 2018.

    These three-year trials will assess the benefits of different constraint-mitigation strategies, such as seeding strategies, soil openers, fertiliser placement and wetting agents.

    Such approaches tend to be low cost compared with more intensive soil amelioration practices, such as deep cultivation, ripping and spading, which tend to be higher cost, but can deliver relatively long-term gains.

    “There’s a lot of opportunity in the space between more traditional mitigation approaches and very intensive amelioration processes, and through modifying machinery,” she says.

    Dr Macdonald says the final two years of the project will concentrate on assessing the cost-benefits of management practices found to be the most effective in lifting crop productivity on southern sandy soils.

    GRDC Research Code CSP00203

    More information:

    Dr Lynne Macdonald,
    08 8273 8111,
    lynne.macdonald@csiro.au