By June 2022, growers and advisers are provided with improved understanding of the development of topsoil and subsoil acidity, limitations to crop profitability, and improved management practices to address this emerging constraint.
By 2027 the aim of this and other projects is to collectively reduce the current cost of soil acidity in SA by 25%.
1 June 2018 – 30 June 2022
Soil acidity has been a constraint to crop production in Australia for many decades, especially on sandy soils where pH drops rapidly. Low soil pH reduces the availability of nutrients for plant growth and can increase aluminium in the soil solution that is toxic and can impair root growth. In addition, the Rhizobia in most pulses is particularly sensitive to soil acidity.
General increases in crop productivity due to improved genetics and management, plus the expansion of pulses and increased fertiliser nitrogen inputs are expected to increase soil acidification rates, especially in intensively cropped areas growing acid-sensitive lentils, chickpeas, faba beans and barley.
About 2.0M ha of cropping land in South Australia (SA) currently has surface soil acidity (0-10cm < pH 5.5) or is considered acid prone, and this area is expected to double over the next 40 years if remedial action is not taken.
Soil acidity can be corrected with lime, however total applications rates have been well below annual acidification. Between 2015 and 2018 about 100,000 t of lime was applied in SA p.a. but this needs to increase to 200,000 t p.a. to correct current rates of acidification. More importantly, about 3M t of lime is required immediately in SA to raise current topsoil pHs to 5.5.
Lime is moderately soluble and moves slowly in undisturbed soils. Hence, the development of acidity below 5cm is particularly concerning because it cannot be easily ameliorated with top dressed lime under low disturbance, minimum or zero-till systems.
Added to this, current recommendations regarding liming rates are based upon historical research under conventional farming systems, characterised by high levels of soil disturbance and significant mechanical incorporation of surface-applied lime.
The relevance of lime rate recommendations in the context of current farming systems therefore requires validation. In WA some growers are inverting soils and incorporating lime to address subsoil acidity while also overcoming non-wetting, compaction and herbicide resistant weeds. NSW DPI is also leading a GRDC project exploring novel ways to address subsoil acidity with deep placement of ameliorants.
Many growers in the southern region appear to be unaware of the emerging acidity issue or are not convinced the responses to lime justify the cost, time and effort in implementing a liming program.
The GRDC Acid Soils SA project, formally titled New Knowledge and Practices to Address Topsoil and Subsurface Acidity Under Minimum Tillage Cropping Systems of South Australia, is a Grains Research and Development Corporation (GRDC) investment which brings together project partners from South Australia's Department of Primary Industries and Regions, the South Australian Department for Environment and Water, the University of Adelaide, Trengove Consulting, Penrice and AgCommunicators.