ConsultAg consultant Ashton Gray has been conducting canopy management trials that have highlighted the benefits of using plant density targets and a flexible fertiliser approach.
Canopy management trials near Wagin, Western Australia, indicate medium plant density (120 plants per square metre) and tactical nitrogen applications during the growing season can pay off with higher yields – especially in years with a drier-than-average finish.
On the flipside, yields can be penalised if there is a combination of high plant density (180 plants/m2) and too much nitrogen applied at seeding.
The aim of canopy management is to optimise crop yields and inputs by matching:
- plant density to yield potential; and
- nitrogen rates and timing with soil moisture and nitrogen levels.
A well-managed canopy has an optimal number of tillers (green leaf area) for any given season so that moisture will be conserved for efficient grain-fill.
The GRDC is funding the first comprehensive canopy management research for WA’s medium and low-rainfall zones, where the principles for this are not yet clearly defined.
Trial sites were set up from 2011 to 2013 at east Wagin, Kulin, Kellerberrin and Kojonup in WA and coordinated by farm consultancy ConsultAg.
Collaboration was undertaken with Nick Poole from New Zealand’s Foundation for Arable Research. Mr Poole has carried out extensive canopy management research in high-rainfall areas.
At each site, researchers monitored how wheat canopy density affected grain yield, grain quality, disease levels and frost damage.
ConsultAg’s Ashton Gray says yield results from 2011 and 2012 were similar for all plant densities and time of nitrogen application across all treatments at the Kulin, Kellerberrin and Kojonup sites.
He says this was despite very different rainfall patterns in those years, ranging from decile 6–7 to decile 1–2. The plant is very good at altering the number of stems it converts to heads and head weight, resulting in these similar yields. These yield components reflect the season and the wheat plant’s ability to adjust when it is stressed.
He says the results were strongly influenced by high mineralised soil nitrogen levels at seeding. However, at the Wagin trial, researchers were able to manipulate the canopy in 2012 to cause significant yield variations.
They used seeding rates of 35, 55 and 80 kilograms per hectare and a standard 40kg/ha of nitrogen was applied at three different timings across the trial.
Timing of nitrogen application varied from all up-front, split at seeding and GS31, and split at seeding, GS14 and GS31.
Findings from the Wagin site in 2012 included:
- the lowest yield of 1.82t/ha occured when all nitrogen was applied up-front, combined with a high plant density (180 plants/m2). These two factors reduced yields significantly (by up to 500kg/ha)because the canopy outgrew its yield potential and there was not adequate moisture conserved for grain fill;
- medium seeding rates (plant density of 120 plants/m2) and split nitrogen produced reliable yields of about 2.33t/ha;
- the highest yields, 2.38t/ha and 2.23t/ha, were also achieved by low (plant density of 75 plants/m2) or medium seeding rates and all nitrogen applied up-front;
- crops could reach yield potential using high seeding rate and delayed nitrogen application; and
- ryegrass biomass fell as seeding rate increased.
Mr Gray says these results highlight that wheat crops can be ‘overcooked’ in some years when seeding rates are too high and too much nitrogen is used up-front
“There is too much biomass that gets droughted when there is a lack of finishing rains and yield losses can be as much as 1t/ha,” he says.
“We have shown in this environment, in a low-to-average-rainfall year, growers can target medium sowing rates and be more flexible in applying nitrogen to play the season as it unfolds – without affecting yield.
“Not overgrowing the canopy conserves soil moisture, reduces disease pressure and finishes crops better. Splitting nitrogen applications is a good risk mitigation strategy, especially if the long-term forecast is not promising or subsoil moisture levels are low.”
Mr Gray says timing of split nitrogen applications did not affect wheat yields in the Wagin 2012 trials. The plants compensated for seasonal conditions by altering the number of stems converted to heads and head weight to produce similar yields
He says the research team has been fortunate to be able to assess the impact of canopy management in WA’s low and medium-rainfall zones in years with a dry start and wet finish (2011), wet start and dry finish (2012) and a good start and good finish (2013).
Final results from the 2013 harvest will be available in coming months. These will help to validate previous trial results and feed into canopy management principles already learnt from research in other grain growing areas, including high-rainfall zones in South Australia, Victoria and New Zealand.
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