Know your soils before spending on amelioration

Deep ripping trial results show importance of understanding soil types


Agronomy
DPIRD research officer Wayne Parker is investigating the costs and benefits of topsoil slotting plates in the deep ripping process.

DPIRD research officer Wayne Parker is investigating the costs and benefits of topsoil slotting plates in the deep ripping process.

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Trials across Western Australia are assessing the longevity benefits of deep ripping.

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Results from deep ripping trials across Western Australia are illustrating the importance of understanding your soil types before investing in soil amelioration strategies.

A total of seven trials were run at Binnu (two trials), Beacon, Moora, Ongerup, Broomehill and Munglinup, investigating the longevity of the benefits from deep ripping, and topsoil slotting plates on yields.

Soil types included various yellow sands, morrell soil, duplex sand over clay, duplex sand over gravel, clay duplex.

Western Australian Department of Primary Industries and Regional Development (DPIRD) research officer, Wayne Parker, who is managing the trials, says the varying soil types across the seven different trial sites showed very different responses to the treatments over the four years of the trial.

Four treatments at all sites included:

  • A control
  • Deep ripping to 300 millimetres
  • Very deep ripping to depths of between 400-600mm depending on soil types
  • Very deep ripping with topsoil slotting or inclusion plates.

Topsoil slotting plates are a pair of steel plates that attach to the rear of the ripping tine, up to 140 mm apart, working below the soil surface to hold open a 'slot' that is back filled by topsoil.

The trials were ripped in early 2015, and all sites and yield responses were monitored throughout the subsequent four years.

DPIRD research officer Wayne Parker assessing root development and structure in a Morrell soil.

DPIRD research officer Wayne Parker assessing root development and structure in a Morrell soil.

Mr Parker says the trials were assessing the long-term effects of deep ripping at varying depths, the value of adding top soil inclusion plates onto any deep ripping process, and the longevity of deep and very deep ripping effects under a controlled traffic farming system.

He presented his findings to this year's 3rd International CTF Conference in Ballarat.

"The responses to topsoil slotting varied significantly from site to site, with the biggest, and longest lasting responses occurring at the loamy yellow sand site at Moora from both the very deep ripped treatment and the very deep ripped plus top soil slotting plates treatment," Mr Parker says.

At this trial site, topsoil slotting plates provide yield improvements of 300 kg/ha four years after the amelioration treatments were implemented.

"We are also still seeing positive results four years after the very deep ripping plus top soil inclusion plate treatments at Munglinup, with yield increases of 200 kg/ha," Mr Parker says.

In most trials, he says there continues to be a positive response to the very deep ripped, and the very deep ripped plus top soil inclusion plate treatments, but the extent of those responses has been varied.

At the Binnu site, where both trials were on yellow sand, the responses were not as conclusive as the trials in both Munglinup and Moora but soil strength continues to remain low, below 1.5MPa, in each of the very deep ripping plots to the depth of ripping after the four years.

"This is a positive result because it means the plant roots have greater ability to access water and nutrients at depth," Mr Parker says.

We are also still seeing positive results four years after the very deep ripping plus top soil inclusion plate treatments at Munglinup, with yield increases of 200 kg/ha - DPIRD research officer Wayne Parker

However, not all trial sites showed a positive response to the three treatments.

"At the Beacon site, which is morrell red clay with a carbonate base, we actually saw a negative yield response to ripping without topsoil slotting plates, which we suspect is because of the sodicity at depth restricting plant growth," Mr Parker says.

He says this reinforces the message to growers that different soil types respond differently to amelioration strategies.

"It also suggests that soil constraints, such as sodicity, boron toxicity and low pH levels must be identified and understood prior to any amelioration activities," Mr Parker says.

Soil constraints can be tested using laboratory services, and hard pan compaction can be tested using a push rod penetrometer. Penetrometers are available for purchase at most machinery dealerships, or online.

In regard to the long-term effects of implementing controlled-traffic farming principles after deep tillage treatments, Mr Parker says research is showing that soil compaction can return after just one pass of a machine.

"If you deep rip your soils to a depth of 450 mm or greater, you can expect to have that soil back to approximately 80 per cent of soil strength - or compaction - with just one pass of a tractor or a sprayer," Mr Parker says.

"So, if you plan on investing in deep ripping, or other soil amelioration techniques, it would make financial sense to implement controlled traffic principles at the same time."

GRDC Research Code: DAW00243

Contact: Wayne Parker, wayne.parker@dpird.wa.gov.au

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