Focus on fallow to boost returns

Photo of Crop Circle Consulting tactical fallow trial site at Mingenew, WA

An aerial image taken in June 2016 shows the scale of the Geraldton RCSN-supported Crop Circle Consulting tactical fallow trial site at Mingenew.

PHOTO: Crop Circle Consulting

Improving spray fallow techniques for moisture and nutrient conservation, weed control and higher grain returns is the aim of trials in the Geraldton and Kwinana East port zones this year.

A tactical fallow is becoming increasingly popular in lower-rainfall parts of these regions to reduce risks associated with seasonal variability, herbicide-resistant weeds and growing non-profitable crops in poor years.

Subsequent crops should be healthier, have a lower weed burden, produce higher grain yields and be more likely to generate a higher two-year gross margin than growing two low-yielding cereal crops.

But a clean spray fallow can be costly to set up in a low-rainfall environment, especially if there are multiple winter and summer weed germinations. There is also concern about reliance on glyphosate in this phase.

To boost grower confidence in the system, the GRDC’s Regional Cropping Solutions Network’s (RCSN) Geraldton and Kwinana East groups are supporting local research into:

  • the effectiveness of summer and winter weed control by a wide range of herbicides;
  • crop tolerances to residual herbicides in the treated soil;
  • application of herbicide-resistance management practices, especially for the herbicide groups that the residual herbicides belong to; and
  • grain yields and quality from growing crops to full potential on stored winter and summer rainfall.

Northern agricultural regional trials

Crop Circle Consulting principal Grant Thompson set up spray fallow trials near Mullewa and Mingenew in 2015 using 24 knockdown and residual herbicide options and a range of new crop technologies.

These are continuing in 2016 and include two-gene Clearfield® wheat (CL); imidazolinone (IMI) tolerant barley; a new short-season Clearfield® canola (CL); and a dual-tolerant triazine-tolerant/RoundupReady® (RT) canola.

Grant says some of the key findings to date from the Mullewa site include:

  • a range of IMI herbicide treatments are showing potential suitability for fallow or pre-emergent use under the CL wheat system with little or no yield penalty;
  • the same three top-performing IMI herbicide treatments in CL wheat plots provided the highest yields in the short-season CL canola plots in 2015;
  • in April 2016, the 5 to 10-centimetre soil layer was noticeably wetter in the fallow plots from 2015, compared to the wheat-on-wheat plots, and they were more conducive to a seeding opportunity; and
  • in June 2016, the IMI-tolerant barley had emerged strongly compared to the other cereal varieties, especially on fallow plots from 2015.

Grant says some of the key findings to date from the Mingenew site include:

  • the highest-yielding and highest economic return wheat plots in 2015 tended to be where the middle (and lower) rates of several IMI herbicides were used;
  • in May 2016, the CL wheat plots that were planted back-to-back with CL wheat were showing fewer herbicide effects than those planted on fallowed plots from 2015;
  • non-tolerant wheat and barley were showing less vigour and biomass in early winter 2016 on plots where higher rates of the IMI herbicides were applied in 2015;
  • to June this year, CL wheat and barley were showing much less response to the varying rates of IMI treatments applied in 2015 and the tolerance of the CL barley, in particular, to IMI residues appeared to be very robust; and
  • CL canola at this site appeared to have very good tolerance to all rates of some IMIs and all rates of the two triazine treatments.

Eastern grainbelt trials

RCSN-supported trials at Wyalkatchem are being carried out by Quade AgriServices Landmark.

Some of the key results, to date, include:

  • highest 2015 yields were where the highest rates of two IMI herbicides were used;
  • there were few significant yield differences between plots where any of the IMI products/rates were used; and
  • triazine treatments were very damaging to the CL wheat.

At each trial site there are soil moisture probes measuring soil water content and plant-available water.

Deep soil testing is being conducted to monitor changes in soil chemistry, fertility, particle size and any constraints across the three years of the trials.

More information:

Grant Thompson,
Crop Circle Consulting,
08 9965 2521,

Useful resources:

'Fallow spray techniques explored for WA's low rainfall zones' – GRDC RCSN video

'Summer fallow spraying' – fact sheet

'Group A herbicides in fallow' – fact sheet

Summer Fallow Weed Management manual

– wheat and canola (western)

Integrated Weed Management Hub


End of Ground Cover issue #124 western edition

Ground Cover Supplement will be back in the November–December issue.

Why not check out the latest news from other regions?
North: To windrow or not to windrow
South: Hot narrow burn keeps weed seeds down

GRDC Project Code CRC00004

Region West