Step-ups in profit become career milestones
Delving and spading has enabled South Australian grower David Giddings to reach what he terms “the next level” in productivity and profitability on his 3000-hectare property at Wanilla on the Lower Eyre Peninsula.
Testifying to this step change, David says the soil amelioration works, which were also his cue for applying lime, gypsum and trace elements, have lifted yields and gross margins for wheat, canola, barley and oats by 20 per cent in the past three years.
Looking at such farm business gains from a long-term perspective, the Giddings’s paddock history shows that lime applications to address high soil acidity, plus adoption of new management practices and technologies dating back 20 years, raised average wheat yields from two tonnes a hectare to 3.6t/ha.
Now, delving and spading look set to further boost their long-term wheat yield average, and following good seasonal conditions in 2016, David was anticipating he might achieve a 5t/ha wheat average when this harvest was measured. “In my farming career I have seen yields almost double,” he says.
David estimates the work to modify the top 40 centimetres of the soil profile – which was staggered over three summers from 2012 to 2014 – has raised his water-holding capacity from about 25 millimetres to 62.5mm (of rainfall equivalent).
This on-farm calculation is consistent with the findings of Lower Eyre Agricultural Development Association (LEADA) trials in 2008 and 2009 that showed delving and spading provided a two-fold increase in the water-holding capacity of duplex soils.
Leading the GRDC-funded LEADA study, South Australian Research and Development Institute (SARDI)* researcher Andrew Ware says the trials highlighted that delving and spading are needed to be able to consistently improve grain yields on duplex soils.
Importantly, for David, the profitability jump in the first year following the soil amelioration operation saw him mostly recoup the costs of the works in just one season. This included $756,000, or $450/ha, spent on delving and spading, and incorporating lime, gypsum, copper, zinc and manganese, across 1680ha.
He believes the cost benefits arise mainly from each plant’s ability to access more soil water during the growing season after delving and spading. David explains how restructuring his duplex sandy loams over clay has allowed both water and plant roots to better infiltrate the soil profile: “Using delving to fracture clay in the subsoil and bring it to the surface has allowed roots to better penetrate the soil.
“Spading to loosen and mix the subsoil layers of clay and gravel with sandy loams near the surface has also reduced the non-wetting effect of our sandy loam topsoil that tended to repel water.”*SARDI is a division of Primary Industries and Regions SA