Innovative approaches to managing subsoil acidity

Soil acidity is one of the few soil constraints to agriculture for which there is a profitable solution. Subsurface acidity requires a more direct intervention approach to manage than topsoil acidity.

ACHIEVEMENTS

  • Where sufficient lime has been applied for long enough, soil pH profiles can be recovered or maintained at or above minimum pH targets.
  • The extent and severity of subsoil acidity is greater in sandy soils where little or no lime has been applied.
  • The amelioration of soil acidity provides protection to the soil resource. By increasing the production biomass soil cover is increased, water loss and leaching of nutrients due to poor root growth is also reduced with potential off-site environmental benefits.
  • If left untreated soil acidification, particularly in sandy soils, will continue to impact on the profitability of dryland agriculture.

OVERVIEW

Soil acidity (low soil pH) costs Western Australian (WA) agriculture an estimated $500 million each year in lost productivity and more recent assessments have increased this to potentially more than $1B. Yet in many areas soil acidity continues to get worse despite a recent and encouraging increase in the rate of use of agricultural lime in WA. Approximately 70% of surface soils and, of greater concern, 50% of subsurface soils (below 10 cm) are below the recommended minimum targets of pH 5.5 and 4.8 (in calcium chloride). Subsurface acidity reduces crop yield through the effects of toxic aluminium restricting root growth and therefore access to moisture and nutrients later in the season.

Historically, insufficient lime application has failed to manage soil acidification in WA, resulting in much of the sandier soil developing subsurface acidity – in some cases to a depth of 40–50 cm or more. Conventional application of surface applied lime takes many years to treat acidity deeper in the soil profile and often too little lime is applied for this to occur at all. Consequently growers are looking for a ‘quick fix’ to the subsurface soil acidity problem, with a number of different products and solutions having been proposed to ameliorate acidity.

With uptake of strategic tillage in recent years to bury herbicide resistant weed seeds, disturb and mix water repellent topsoil and incorporate nutrients that have become stratified, an ideal opportunity to incorporate agricultural lime (and potentially other products) to depth is provided. In WA there is clear evidence that shows with appropriate inputs of lime, the soil pH profile can be recovered and maintained at or above the minimum pH targets, removing soil acidity as a soil constraint to agriculture.

See www.agric.wa.gov.au/soil-acidity/soil-acidity-western-australia.

This project aims to evaluate a range of new and innovative methodologies designed to increase the efficiency with which subsoil acidity is treated in the field compared to conventional surface application of agricultural lime and basic incorporation of surface applied lime. Through a series of glasshouse experiments, field trials and demonstrations, we will develop recommendations for appropriate management practices.

Unless significant gains are made towards managing soil acidity, and in particular subsurface acidity, through more effective use and application of agricultural lime in the near future it will become increasingly difficult for WA growers to afford to apply the appropriate amount of lime – the consequence of this is that in our changing climate cropping options will become limited.

The project team includes Gaus Azam, Craig Scanlan, Daron Malinowski (DAFWA); Paul Damon, Zed Rengel (UWA); Brian Hughes, Brett Masters (Rural Solutions) and James Fisher (Desiree Futures).

FUNDING

Collaborative project funded by the GRDC in collaboration with Royalties for Regions, the Department of Primary Industries and Regional Development: Agriculture and Food Division (formerly DAFWA) and UWA.

CONTACT

Chris Gazey

Department of Primary Industries and Regional Development (DPIRD)

chris.gazey@dpird.wa.gov.au

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