Deep ripping combined with topsoil slotting key on deep sandy soils
Trials in the Western Australian wheatbelt have found deeper ripping combined with topsoil slotting can increase yields from sandy soils by more than deeper ripping alone.
Results from Department of Agriculture and Food trials focused on overcoming subsoil compaction and other constraints were detailed at the GRDC Grains Research Update in Perth earlier this month by senior soil scientist Paul Blackwell.
The 2015 trials, supported by the Grains Research Development Corporation (GRDC), found topsoil slotting, with soil inclusion plates attached to the rear of deep ripper tines, could deliver increased yield from deep sandy soils.
Cropping soils with sandy textures at least 500mm deep, needed deep ripping to 550mm or more to decompact hardpans and topsoil slotting to allow the crop to yield closer to its potential in a controlled traffic farming (CTF) system.
Eight trial sites with deep sandy or clayey soils, reaching from Binnu to Esperance, were decompacted.
The sites were sown using farm seeders and ripped using a research deep ripper, designed and built with shallow leading tines and topsoil inclusion plates.
To examine the economic value of the deeper ripping and topsoil slotting Dr Blackwell calculated the additional profit made for each dollar spent.
First year returns on investment for trials with dry growing seasons in 2015 ranged from $6 to $16 per dollar invested.
Best short-term returns on investment for many of the deeper, sandier soils came from deeper ripping with topsoil slotting.
The combination of deeper ripping and topsoil slotting also helped reduce grain losses from dry and hot spring weather by providing some nutrients and water from the slot zone when the topsoil had dried out.
If slotting maintains the decompaction response longer it will provide very good returns on investment.
Soil ameliorants (lime, gypsum or organic matter) can also have more effect on sandy or clay textured subsoils and offer better return on investment when slotted with topsoil at the time of deep ripping if there are additional constraints.
Further investigation into application rates is required.
The deeper ripping on the heavier soils had variable effects, likely due to the presence of other subsoil constraints such as transient salinity that may be limiting yield more than compaction.
However, the possible benefits to Morrel soils and grey clay of deeper ripping with topsoil slotting and addition of organic matter are very encouraging and warrant further investigation.
Dr Blackwell said the return on investment preliminary analysis needed nesting within a whole farm economic analysis.
Best bet suggestions are to deep rip deep sandy soils with topsoil slotting to 500mm or deeper and set up CTF in the same season.
Also, apply lime if the soil is acidic, and test strips of deep ripping and topsoil slotting with or without top-dressing lime.
For further information refer to Deeper ripping and topsoil slotting to overcome subsoil compaction presented at the 2016 GRDC Research Updates.
For more information contact Paul Blackwell, Research Officer, Geraldton on +61 (0)8 9956 8537 or Bindi Isbister, Development Officer, Geraldton on +61 (0)8 9956 8532.