Future proofing the soils of southern and central NSW from acidification and soil organic carbon decline
Author and organisation: Helen McMillan CWFS, Jason Condon and Helen Burns NSW DPI.
Producer and advisor surveys indicate that current approaches to managing soil acidity are based on research and guidelines from the 1990s, and were therefore developed under very different and less productive farming systems. Most fertiliser, lime and crop selection decisions are guided by soil sample analyses collected at traditional depths of 0–10 cm. Depending on the crop or pasture sequence, the common trigger to apply lime is when soil pHCa is around 4.5–4.8. It is applied at minimal rates to remove toxic aluminium (target pHCa 5–5.2).
These traditionally reactive approaches and a failure to monitor the effectiveness of acid soil management programs are responsible for widespread, undetected subsurface acidification in marginally acidic soils, as well as those with a long history of soil testing and lime application (Burns and Norton 2018). Recent studies challenge the short-term focus of current acid soil management programs:
Li et al. (2019) recommended revising pH targets and re-liming intervals in order to address subsurface acidification, proposing soil maintenance pHCa above 5.5 in the 0–10 cm surface layer to gradually increase subsurface pH.
Condon et al. (2020) highlighted inadequacies of current acid soil management programs and reinforced the need for a shift from mitigating soil acidity to prevention, particularly in zero tillage farming systems.
Conyers et al. (2020) concluded that ongoing reaction of limestone and reacidification processes influenced soil pH and that ‘the slow but measurable improvement in subsurface acidity, and the sustained residual value to grain yield’ required a long-term approach to amelioration efforts to manage and prevent subsurface acidification.
This article reports preliminary results from the first year after liming treatments were implemented from the paddock scale site at Trundle in 2020. This site is one of five designed to monitor long-term changes in soil chemical properties as influenced by various liming rates and management to develop a predictive model to improve decision-making around optimum lime rates and incorporation strategies.
- Location: approx. 25 km north of Trundle NSW
- Soil type: sandy loam; soil pHCa range of 4.3-5.6 down to 30 cm
- Farming system: continuous cropping with pulses and canola included in the rotation
- Treatments applied: March 2020
- Growing season rainfall (April-October): 430 mm