Unlocking Crop Yield Potential by Addressing Subsoil Constraints

Preliminary results in southern NSW show potential to improve productivity on soils where access to plant available water (PAW) is currently restricted by a range of subsoil constraints. Research conducted by the NSW DPI at Rand and Grogan in 2017 and 2018 is assessing the potential for deep (40cm) placement of organic ameliorants to improve the structure of sodic subsoils. Many soils inundated by 2016 flooding across southern NSW, have also performed poorly in 2017 and 2018, despite having water deep in the soil profile. This research aims to unlock deep stored water and allow crop roots to explore the full depth of soil.

Treatments include deep and shallow placement of manures, gypsum, pelletised straw, liquid fertiliser and other amendments, compared to a do-nothing control and deep ripping without amendments. Treatments are applied once, with changes observed over subsequent years, to measure the effects. Variety screening is also being carried out to determine which wheat varieties perform better than others on these hostile soils.

Initial yield responses from some treatments have been impressive, considering dry conditions in 2017, with the best treatments yielding more than 1.0 t/ha above the control. Similar trials in Victoria have shown up to 70% yield gain by removing subsoil constraints. Frost assessments carried out at the Rand site in September 2018, revealed severe stem frosting in the untreated plots, plus the surrounding paddock. By contrast, many plots with subsoil amelioration treatments showed little, if any frost damage. This can be seen in Figure 1 below.

Specialised machinery has been developed to place soil ameliorants at the appropriate depth, under trial conditions. Engineering firms have been engaged as part of the research work, with the intention of producing commercial scale machinery. While the cost of such remediation, deep in the soil profile is significant, previous research from Victoria suggests that the benefits last for several years.

Figure 2 and Figure 3 below show the improvement in subsoil structure from amelioration, compared to untreated soil.

This research is being expanded in 2019, with one to two additional trial sites being established early next year. More information on this research can be found at: https://grdc.com.au/resources-and-publications/groundcover/groundcovertm-130-september-october-2017/trials-dig-deep-to-ameliorate-sodic-soils or by contacting Ehsan Tavakkoli, NSW DPI. ehsan.tavakkoli@dpi.nsw.gov.au