WA cropping plumbs new depths
GroundCover™ Issue: 123 | 04 Jul 2016 | Author: Brad Collis
Growers in WA are using powerful deep-ripper implements to break through hardpans and allow plant roots and nutrients to reach deeper, more productive depths
Soil compaction and its remedy – deep ripping – has been the hot topic in Western Australia over the past 12 to 18 months as more and more growers report significant production improvements resulting from crop roots being able to reach deeper into the soil profile.
The ripping, down to 550 millimetres, is allowing crops to overcome severe growth constraints caused by soil being packed harder and harder by increasingly heavier machinery. Compounding this is a cluster of other constraints that often come together – non-wetting soils, and subsoil acidity and sodicity.
The prize for roots able to breach these barriers is the precious reserve of soil moisture half a metre to a metre down.
In a drying environment where more moisture equals more grain and profit, plant root access to this deeper moisture is vital.
Department of Food and Agriculture, WA (DAFWA) development officer Bindi Isbister says soil compaction has become top-of-mind for an increasing number of growers because it has been moving deeper down the profile beyond the depth of standard deep rippers owing to the increasing weight of today’s machinery. This compaction has been restricting access to deeper moisture, and consequently is a significant constraint on yields.
As a general rule of thumb Ms Isbister says a 10-tonne axle weight causes compaction down to 300mm. Most new large machinery, such as headers, tractors, aircarts, chaser bins, and even spray booms, exceed this weight. A modern header can weigh 30t when loaded, causing compaction down to 400 to 600mm.
The issue has led to considerable experimentation in recent years and a lot of growers are either importing massive deep-ripping implements from overseas or making their own. DAFWA researcher Dr Paul Blackwell has built a research ripper able to work down to 600mm to evaluate new ripping methods in GRDC-funded trials.
Ms Isbister says some form of renovation such as deep ripping has long been required in WA soils – it is just that compaction has worsened at the same time as a drying climate has made it even more crucial for crop roots to reach deep moisture.
She says the region’s sandy soils generally have less than 35 per cent clay and so have little capacity to naturally swell and crack to remove compaction. Shallow compaction down to 200 to 300mm can be removed by standard deep ripping or other soil renovation methods such as mouldboard ploughing or spading. These practices also help alleviate water-repellent soils and subsoil acidity (by incorporating lime).
Now, the emphasis is on ripping much deeper and supplementing the actual ripping with ‘topsoil slotting’. This involves fitting steel ‘inclusion’ plates behind a ripper’s tynes to direct the loosened topsoil into the furrow. This has the effect of burying topsoil and surface ameliorants such as lime, gypsum or organic matter. This means soil ameliorants, nutrients and soft topsoil can be mixed together at depth and in moist conditions. This not only improves soil structure at depth, but also sets up conditions much more conducive to higher yields.
In trials during 2015, deep ripping to 550mm combined with topsoil slotting produced yield increases of 1 to 1.7t/hectare at four different sites. The return on investment ranged from $6 to $16 per dollar invested.
With the increasing number of growers taking a serious look at deep ripping,
Ms Isbister is keen to capitalise on the interest by urging growers to plan their approach to ripping in conjunction with implementing controlled-traffic farming (CTF).
She says CTF will minimise re-compaction and therefore increase the return on investment of expensive soil-amelioration techniques.
“Up to 80 per cent of compaction damage occurs in the first pass, so adopting CTF is the best way to minimise re-compaction and maximise the longevity of soil renovation treatments,” she says.
“Increasing the longevity will improve the economics of treatment. For example, assuming a treatment cost of $60/ha for deep ripping to 550mm and a yield increase of 500kilograms/ha, the difference in benefit between the treatment remaining effective for three years and seven years is $4.70 and $10.80, respectively, for every dollar spent.”
Ms Isbister explains that the basic principle of CTF is reducing the percentage of the paddock wheeled in any given season so that traffic is confined to set wheel tracks, leaving uncompacted beds for plants to grow in and to more easily access moisture and nutrients.
“It is not uncommon for farming operations in the WA wheatbelt to cover 40 to 60 per cent of the paddock with wheels in a single season. The target ‘wheeling’ for a CTF system is about 11 to 15 per cent.
“We also recommend deeper ripping be conducted under a CTF system due to the very soft soil conditions after ripping. For CTF you would remove or lift the ripper tynes in line with the planned wheel tracks, leaving a solid track for the seeding, sprayer and harvest machinery to follow.”
She also points out that removing the tynes on wheel tracks can reduce the horsepower output and save 15 per cent of the total paddock cost of ripping.
Ms Isbister recommends using a shallow leading-tyne configuration or ripping in two ‘bites’ to reduce the horsepower requirement and achieve more even break out (less large clods): “A heavy hydraulic crumbler roller is also useful to firm, level and crush clods to create a more even seedbed.”
In terms of implementing CTF she emphasises that there is no ‘one size fits all’ approach because of the significant variation in machinery sizes. However, she offers the following tips:
- Decide on imperial or metric. Forty feet is not 12 metres, but 12.2m. A small difference, but enough to make it hard to match Australian and imported machinery. Choosing to work in one or the other helps keep it simple.
- Then choose an operating width. Machinery matching in multiples of 12m or 40 feet is the most common. The ideal machine to work from when deciding the width is the header as it is the heaviest machine, the hardest to modify and can have the widest wheelbase. A compromised system of a 40-foot header, 60-foot seeder and 120-foot sprayer is becoming increasingly common in WA.
- When you measure bars and sprayers remember to add one row or nozzle spacing.
- Check the header cutting-bar width. Often machinery is sold at a certain width but it may cut more or less.
- When thinking through the best option, consider what system you might like to have in five to 10 years’ time.
Ms Isbister says the best way to decide what width will suit your system is to map out your machinery widths and tracks either using graph paper or the ‘Wheeltrak’ calculator. This tool was developed by PrecisionAgriculture.com.au.
More information:Bindi Isbister,
08 9956 8532,
Controlled traffic farming – fact sheet
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