Ripping into climate change

Image of a precision sprayer

Craig Thompson bought a WEEDit® precision sprayer seven years ago and says it has become a crucial tool for summer weed control.

PHOTO: Brad Collis

A stark drop in growing-season rainfall in WA’s northern wheatbelt means growers have to get crop roots much deeper into the soil profile to access moisture

Over the past 20 years Craig Thompson has lost about 50 millimetres of his growing-season rainfall and it is with some understatement that he quips, “that’s a lot of water from a bucket that was only ever about 270mm to start with”.


Growers: Craig and Sam Thompson, Kim and Gloria Thompson
Property: ‘Yamma’
Location: Yuna, Western Australia
Cropping program: 7300 hectares wheat (Magenta, Mace, Bonnie Rock and Impress CL Plus)
Average growing season rainfall: 160mm (annual average for past 15 years 230mm, down from historic 270mm)
Soil type: 50:50 sand and ‘red country’ comprising about 10 per cent clay
Soil pH: 4.5 to 6 

It means he and others in the far north of the Western Australian wheatbelt no longer receive the soaking winter rains that generally kept the top soil layer moist through the season. Those days are gone and the moisture needed to sustain crop growth tends to be deeper in the profile and invariably on the wrong side of a root barrier created by acidity and aluminium toxicity or compaction.

Not surprisingly, Craig’s father Kim was among the first to undertake widescale deep ripping in the late 1990s.

“We did the whole farm and now we’re going over a second time,” Craig says. “I would have liked to have done it sooner, but high fuel prices combined with a run of bad seasons through the early 2000s meant deep ripping had to be put on the back burner.”

All fired up

Now, however, the economics have shifted and over the past 12 to 18 months enthusiasm in the district for deep ripping has reached new heights: “What got people fired up were the trials on Brady Green’s property. He went quite deep, down to 500mm, and we were all surprised by how much lime and soft topsoil got dragged down into the profile behind the tynes,” Craig says (see Drought inspires a cropping paradigm shift).

“He dug soil pits and you could see where the lime had reached and it was very exciting. Everyone knew there would be some lime incorporation, but not to the extent that occurred.”

Craig thought that if the soil could be kept open longer, albeit for a fraction of a second, you would get even more lime and surface soil deeper into the profile. This led to the concept, and rapid adoption, of inclusion plates. These are bolted behind a tyne to immediately direct loosened topsoil into the furrow. It delivers soil ameliorants such as lime, gypsum or organic matter deeper into the profile and also creates a soft channel for roots.

In trials, and in practice on many properties last year, the jump in yields was nothing short of historic.

In GRDC-supported Department of Food and Agriculture, WA (DAFWA) trials, deep ripping to 550mm combined with ‘topsoil slotting’ using inclusion plates produced yield increases of 1 to 1.7 tonnes per hectare at four different sites. The return on investment ranged from $6 to $16 per dollar invested (see WA cropping plumbs new depths).

In Craig’s case, 1.33t/ha is a profitable wheat crop. Where he deep ripped, to 430mm, and with inclusion plates, his yields averaged 2t/ha.

“Afterwards on our sandplain country we dug a hole as deep as we could with a 1.5-metre shovel and the roots were still going. It was an impressive sight.”

Paradigm shift

Craig sees the results as a paradigm shift: “If we can get crop roots down to where there is moisture, even if it is a metre down, that crop is ‘in the bank’.”

He describes the despair a decade ago as the climate was drying and before deep ripping, when after a poor harvest following a dry finish, moisture could be found just 30 centimetres down, yet had been beyond the reach of roots.

“It was devastating realising your crop hadn’t been able to reach moisture because from 20cm to 30cm down there is a hostile layer – pH, aluminium toxicity or a hard pan. That’s why the cornerstone of our cropping now is to give roots every chance to get through this barrier.”

Craig believes deep ripping could be the turning point in managing the loss of winter rain and elevating farm productivity.

“The climate trend seems to be heading towards more summer rain, so holding onto that moisture has to be the basis of our system.”

His cautionary note is the need to try to avoid crops getting away too quickly and burning off.

“We need a wheat variety we can plant in the middle of April and be able to handle the early stress because temperatures are still high. In other words a variety that will just sit there for a few weeks and not bolt.”

He says MagentaA is getting close to this, so he is optimistic the right variety is within breeders’ reach.

Craig describes his 7300ha cropping regime as unconventional in that he grows no break crops, just wheat-on-wheat – with the aid of Clearfield® varieties.

“Our growing season rainfall is so low – now less than 200mm – that we don’t really have a disease problem,” he explains. “When we do need a break in the rotation we just put in a fallow.”

He says they were growing lupins in the early 2000s, but it became too hard to control wild radish in the crop, and profitable yields were hard to maintain. Canola also became risky in the drying climate, whereas with Clearfield® wheat he can use in-crop herbicides Midas® and Intervix® to control the main weeds – brome grass, wild oats and barley grass.

Holding on to every drop

Craig says that wheat-on-wheat, with the aid of Clearfield® wheats, has simplified the system and allowed him to concentrate on the single most important element – holding on to every drop of rain that falls.

This, of course, has made summer weed control an absolute priority. He bought a WEEDit® sprayer, which uses infrared sensors for precision weed-kill, seven years ago and says it has paid for itself many times over.

“Our herbicide bill through the summer months is now 15 per cent of what it once was.”

Craig says he is always aware of the challenge of growing grain at the top end of the WA wheatbelt, but if anything he is more optimistic about the future than ever, despite the changed climate.

“There is no denying it’s tough, but I’d like to think my boys will be able to farm after me and I’m confident we are laying the foundations for a cropping system that will be robust enough for that to happen,” he says. 

Image of Craig Thompson

For Yuna grower Craig Thompson, holding onto every drop of summer rain is crucial and he says the WEEDit® unit he bought seven years ago has reduced his summer herbicide costs by 75 per cent.

PHOTO: Brad Collis

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WA cropping plumbs new depths

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