Low rainfall fallow options tested
GroundCover™ Issue: 120 | Author: Melissa Williams
By strategically knocking down weeds in fallow paddocks at seeding time and keeping these clean from weeds until the next sowing, vital soil moisture is conserved for the subsequent crop.
This next crop should be healthier, cleaner of weeds and produce a better two-year gross margin compared with two low-yielding cereal crops.
Campbell Jones is among a new wave of growers in WA’s eastern wheatbelt who are starting to use a spray fallow to reduce the risks associated with seasonal variability, herbicide-resistant weeds and growing non-profitable crops in low-rainfall years.
He farms with his wife Amanda and parents Brian and Lyn at Wyalkatchem and first trialled a fallow in 2014 on 15 hectares next to a medic pasture and a wheat-on-wheat paddock.
Soil testing in summer 2014-15 showed the fallow area had a full ‘bucket’ of water down the soil profile and higher mineralised nitrogen (N) levels compared with the medic and consecutive wheat areas.
These early findings prompted Campbell to add a fallow of 360ha to his cereal and canola cropping program in 2015 and the area will be sown to canola this year.
Campbell says he achieved good control of the main winter weeds – annual ryegrass, wild oats and wild radish – in the fallow area last year.
This summer he is closely monitoring the residual effectiveness of the winter herbicide system for controlling the problem weeds of kerosene, button and windmill grasses, caltrop and paddy melon.
“One danger of a fallow is taking a cashflow ‘hit’ by taking a paddock out of wheat for a season,” he says.
“However, over time, we hope we will get yield increases and better grain quality from the second-year crops, break the cycle of cereal root diseases and lift our cashflow over several years.”
Campbell is hosting one of three GRDC Regional Cropping Solutions Network (RCSN)-funded trial sites investigating ways to improve a spray fallow in WA’s eastern and northern wheatbelts.
These trials at Wyalkatchem, Mingenew and Mullewa are assessing a range of herbicides, including residual options, and new crop technologies, including two-gene Clearfield® wheat, imidazolinone-tolerant barley, and Clearfield® dual-tolerant triazine-tolerant/Roundup Ready® canola.
Fallow can be costly to set up in a low-rainfall environment, especially if there are multiple winter and summer weed germinations, and there is concern about reliance on glyphosate in this phase.
To boost grower confidence in the system, he says the GRDC RCSN fallow trials aim to provide local data about:
- the effectiveness of summer and winter weed control from a wide range of herbicides;
- crop tolerances to residual herbicides in the treated soil; and
- grain yields and quality from growing crops to full potential on stored winter and summer rainfall.
“The goal is to develop management packages for residual herbicides that can be applied before the start of the winter fallow period to control winter weeds and continue to be effective on summer weeds,” Mr Thompson says.
“We anticipate these treatments will then persist into the next (second) winter cropping season, when a tolerant crop type would be planted into the treated area.
“This winter crop would have access to almost 12 months of stored soil moisture and mineralised nutrients, it should be less labour-intensive to spray and there should be less reliance on current herbicides – having a positive spin-off in reducing herbicide resistance risks.”
Grant says if such crop and herbicide options prove successful, yield advantages could be as high as 0.5 to 1 tonne/ha for wheat and 0.5t/ha for canola and herbicide savings could be about $15/ha to $50/ha (depending on rainfall distribution and soil type).
“In low-rainfall years, this could be the difference between two consecutive loss-making crops or one very profitable crop after a low-cost fallow spray,” he says.
Quade AgriServices Landmark agronomist Bernie Quade, who is overseeing the Wyalkatchem site, says the trials are using soil moisture probes to measure soil water content and plant-available water. Deep soil testing is being used to monitor changes in soil chemistry, fertility, particle size and any constraints over the three years of the trials.
More information:Campbell Jones,
0428 885 603,
Bernie Quade, Landmark agronomist,
0427 266 880,
08 9921 1344,
GRDC Summer Fallow Weed Management manual
GRDC Project Code CRC00004