Plant roots provide deep ripping clues

But many farmers have encountered issues, particularly if clay is not properly incorporated, mixing to a depth usually beyond 15cm (6in).

Anecdotal reports have revealed that while initial crop germinations may improve there have been reports that after two to three years, near the end of the growing season, the clay in the top 10cm (4in) was drawing moisture into that soil layer and drying out the root zone, effectively droughting crops.

And an unintended consequence was a hardening of the topsoil.

This “wick” effect is sometimes observed in the northern Wheatbelt (due to higher evaporation rates in spring) but rarely in the south, especially with adequate incorporation.

For Kojaneerup farmers Tony Goad, and his son Josh, their reaction to the fact they were not achieving the crop yields they expected after claying prompted an investigation which revealed soil compaction was the issue.

It saw them involved in a “ameliorating soil compaction” trial as members of the Stirlings to Coast Farmers group (SCF).

They decided to look at deep ripping as a means of removing soil constraints for crop roots, after observing plants growing down old tree root pathways yielded better.

Visually they appeared as “lumps” in crops and that provided evidence to support deep ripping.

This was supported by soil penetrometer tests showing a deep compaction layer.

The trial was part of a long-term plan to assess deep ripping as a management practice.

In 2014, in their first year, they ripped to a depth of 30cm (12in) but in consultation with Department of Agriculture and Food researcher Jeremy Lemon, the next year they used a DAFWA-made ripper, digging to 50cm (20in).

Last year they went even further, to 75cm (30in), using a Heliripper.

And to establish their deepest trial, they used a bulldozer to rip at 120cm (48in).

Last month, the SCF held its annual trials review day at South Stirlings, where the Goad’s trial results were included in presentations.

Grain yield was increased with 2016 deep ripping to 75cm by 0.5 to 1.1t/ha – 0.7t/ha over the full length of plots.

Yields improved a further 0.2 to 0.7t/ha with ripping to 120cm – 0.4t/ha over the full length of plots.

According to Jeremy, while there was a yield increase on all yield zones and over the whole paddock length, the largest increase was on the poorest zone associated with sand over a one metre depth, increasing yield above no ripping in all zones.

“There was an insignificant residual yield benefit in 2016 from 2014 ripping to 35cm (14in),” he said.

“In 2014, there was up to 0.3t/ha barley yield increase from this shallow ripping.”

At a trial in South Stirling last year, Jeremy said the largest yield increase was from 35cm ripping on a gravel area.

“This is an unexpected result and emphasises the need for replication to verify observations,” he said.

“While we have observed 0.2 to 0.3t/ha yield increases from 35cm ripping, deep ripping on such compacted sand sites often gives larger increases than the 0.34t/ha, measured in this demonstration.

“Harvest results indicate a moderate response to both ripping depths on both soils.”

Jeremy said a likely reason for the moderate result on deep sand was that the acid soil profile to depth prevented effective root function.

Ripping with the same machine at Kojaneerup produced 0.5 to 1.1t/ha grain yield response in 2016.

“The May to October rainfall of 350mm indicates a cereal yield potential of about 4.7t/ha,” Jeremy said.

“The highest plot yield approaches this with a 4.46t/ha result.”

For the Goads, the trials were enough of an encouragement to continue to deep rip with cost benefits showing out from yield responses.

“We only started cropping five years ago because this was mainly a grazing property,” Josh said.

“We’ve been here 13 years but now we’re not running any stock.

“Now it’s a case of evaluating the residual benefits of the rip and longer term we maybe look at CTF (controlled traffic farming).

“Future rips will be aimed at paddocks where we think we can get an economic response.”

There seems little doubt that deep ripping will become a management practice along the South Coast, based on the interest of trial results. Stirlings to Coast Farmers will continue in research partnerships with growers and DAFWA on ways to maximise and retain the benefits in responsive soils.

“There are still lots of questions,” Josh said. “Timing of the rip, how deep, residual effects and other aspects need to be assessed but I think it’s a practice that is heading in the right direction.”