Crop canopy management to achieve higher yields in the better seasons — lessons from hyperyielding and irrigated crop agronomy

Take home messages

• Canopy management techniques should aim to maximise crop growth during the critical period of grain number formation and improve harvest index (conversion of biomass to yield).
• Slower developing feed cultivars express their improved yield potential in the wetter and milder seasons. Consider the feed price spread and yield differential.
• Slower developing genetics typically produce more biomass and have greater yield potential. Interventions such as grazing improve harvest index (HI) but come at the expense of reduced final biomass and thus, yield is rarely increased.
• Irrespective of development type and other management, disease management is one of the key drivers of improving yield and HI in wetter seasons, achieved by both improved genetic resistance and strategic fungicide application.
• Fertile soils in the high rainfall zone (HRZ) limit the ability to manage yield and early biomass production with applied nitrogen in wetter environments. Mineralised N timing, and other canopy management factors, such as plant growth regulators (PGR) and fungicides, are equally or more important.
• Principles of canopy management also apply to irrigated scenarios, however the nitrogen rates required to achieve irrigated canola yields of greater than 4t/ha are not as high as dryland budgets would suggest.
• Minimum durum protein requirements of 13% to achieve DR1 can be met with attention to nitrogen management in irrigated scenarios.
• Canopy management benefits of PGR and fungicides extend beyond the growing season and limit pre-harvest yield losses (lodging, brackling, head-loss) and improve harvest logistics.
• Waterlogging tolerance of barley compared to wheat is poor in wetter seasons, however earlier sowing and slow developing cultivars increase the chances of improved yield recovery.

Hyperyielding crops research

Led by Field Applied Research (FAR) Australia, the Hyperyielding Crops (HYC) project is a Grains Research and Development Corporation (GRDC) national initiative which aims to push the economically attainable yield boundaries of wheat, barley and canola in those regions with higher yield potential. The project team at the time of writing is just completing harvest of the second year of project trial results at five HYC research centres across the higher yielding regions of southern Australia (NSW, WA, SA, VIC and TAS) which have been established to engage with growers and advisers. With the 25 focus farms and the HYC community awards, the aim is to scale up the research results and create a community network aimed at lifting productivity.

Canopy management is key to building and protecting high yielding crops in wet environments (seasons) and irrigated crops

Canopy management is a broad term but fundamentally relies upon adopting techniques that allow crops to intercept more radiation (sunlight) and transpire more water into biomass at the right time in the season to contribute to yield. This is first achieved by ensuring flowering is matched to environment and secondly, that a high proportion of the upper crop canopy leaves remain intercepting light (retain green leaf area, disease control) during the ‘critical period’ for grain number formation (month prior to flowering in cereals). Unlike low rainfall environments, excessive growth prior to stem elongation is unproductive and leads to lodging, shading and poorer light interception in the critical period. Equally nitrogen (N) limitation and/or poor disease control during this period will lower grain number potential and yield either by limiting biomass production or its conversion into yield (harvest index). Harvest indices of greater than 50% should be possible with good management. Therefore, to achieve 10t/ha cereal grain yields, the final biomass needs to be greater than 20t/ha.

While canopy management techniques can improve harvest index, they should not come at the expense of reduced final biomass. For example, grazing (mowing) spring and winter wheats at Gnarwarre, Victoria in 2020 increased harvest index (HI) but yields were not increased due to lower biomass (Figure 1). This trend was also observed at other hyper yielding experiments in NSW and SA. Spring wheats that achieved similar final dry matters as winter wheats yielded lower (lower HI) due to reduced light interception in the critical period from developing under sub-optimal conditions (early) and reduced green leaf area in upper canopy (increased disease infection).

Figure 1. Relationship between dry matter and grain yield (t/ha) across a: Winter wheats (RGT Acrocc and Anapurna), and b: Spring wheats (Scepter and Trojan) at three different management levels, grain only 2. low and 3. high input systems, and 1. grazed systems in 2020 at Wallendbeen NSW, Millicent SA, and Gnarwarre Vic. The dotted line represents aspirational yields that are possible with a harvest index of 50%. The key differences between low and high input are the addition of a PGR, and extra nitrogen (~20—40kg), and one extra fungicide. Grazing simulated by mowing prior to GS30. Management details for Victoria in this example can be found on the FAR Australia website.

Optimising irrigated grains research

The principles of canopy management also apply to irrigated scenarios and during 2020 and 2021, over 50 irrigated research trials (in six crops) were established at FAR Australia’s Finley Irrigated Research Centre (Southern Growers Irrigation Complex) in southern NSW. This has been part of a major regional GRDC investment referred to as the ‘Optimising Irrigated Grains’ project with agronomy and soil amelioration research led by FAR Australia in collaboration with the Irrigated Cropping Council (ICC). Work in canola has been targeted at growing 5t/ha crop of canola and 10t/ha crop of durum wheat under irrigation, and in particular, looking at the canopy management and nutritional requirements for high yielding crops. These canopy management factors include cultivar crop development, genetic disease resistance, fungicide chemistry and timing, and other intervention techniques such as the addition of a PGR, defoliation and additional nitrogen.

Two years of irrigated canola and durum research

Research in canola has indicated that extremely large doses of applied nitrogen fertiliser are not the route to the most economic returns and that crop establishment, absence of waterlogging and healthy soils with good available soil N reserves are the best combination of factors to maximise yield in irrigated canola. In 2020, following wheat, the hybrid 45Y28 RR gave a significant response to applied nitrogen that illustrated an optimum N rate for yield of approximately 160kg N/ha with a yield of 4.55t/ha (Table 1). In 2021, the optimum response was higher at 240kg N/ha with a yield of 3.9t/ha. Although yields in 2021 peaked at a nitrogen rate of 320kg N/ha, the yield was not statistically greater than at 240kg N/ha. Measured levels of available starting N were similar to 2020 (at 129 v. 110kg N/ha (0–90cm)) but unfertilised crops produced considerably lower yields in 2021 with evidence of waterlogging in the winter 2021 that may have both restricted the rooting of the crops and/or generated losses of N from the soil under the anaerobic conditions. In 2020, differences in oil content were small but significant with a 1.2% oil content decline covering N rates between 80–320kg N/ha applied. There were no significant differences in oil content in 2021.

Table 1: Influence of applied nitrogen rate at stem elongation on grain yield (t/ha) and oil content (%) of canola across 2 years.

Durum research at Finley over the last two years (Tables 2 and 3) illustrated much lower available soil N reserves in the 2021 season compared to 2020: 232kg N/ha in the soil profile (0—90cm) following fallow in 2019, compared to 146kg/ha over the same depth in 2021 following canola. Consequently, DBA Vittaroi gave no significant yield response to applied N fertiliser (urea 46% N) at levels between 10–350kg N/ha in 2020, with yields ranging from 6.93–7.43t/ha. By comparison, yields in 2021 were between 4.87–6.74t/ha , with no significant yield response to N application above 100kg N/ha. However, it required another 100kg N/ha of applied fertiliser (200kg N/ha total) to increase protein above 13%, the minimum required to achieve DR1 quality when applied N was split between GS30 and GS32 (pseudo stem erect & second node). However, in a separate experiment, it was illustrated that when N timing was delayed until GS32 and GS37 (flag leaf visible), a protein of 13.4% was achieved with no more 100kg N/ha of applied nitrogen (Table 3) and no loss of yield. (data not shown).

Table 2: Influence of applied nitrogen rate at stem elongation on grain yield (t/ha) and protein content (%) in durum across 2 years.

Table 3. Influence of N rate and timing strategies on grain protein (%) in durum grown at Finley in 2021, based on split application of N at total rates of 0, 100, 200 and 300kg N/ha.

Hyper yielding research: achieving high yields from the better seasons

Consider the genetic potential of the cultivar and delivery price splits between feed and higher quality grades to maximise economic returns

The wet 2021 season and HYC research has highlighted that the increased yield potential of feed wheats and winter barley is expressed in the better seasons and exceeds current commercially available milling wheats and malt barley cultivars. While it is possible to grow higher yield of feed wheats and barley, they need to be profitable. The durum example above shows it is possible to achieve high yields and higher proteins with N management and highlights possibilities to make the most of quality price spreads with management. The HYC results below demonstrate the milling wheats are capable of yielding 8t/ha and milling grade with adequate disease control, whereas feed winter wheats are achieving yields of ~ 11t/ha and greater in the same experiments. It must be noted in southwestern Victoria and in the lower South East of South Australia, milling wheats have often achieved lower yields, and failed to meet milling grades from earlier sowing. Figure 2 below can be used to determine how much higher feed wheats need to yield across different quality grade yield potential environments to equal or exceed milling wheat gross margins. For example; at feed splits of $100 between APW and feed wheat, a feed wheat would have to yield 12t/ha (or an extra 4t/ha) to equal the gross margin of APW yielding 8t/ha (at $300/tonne delivery price). If the spread reduces to $50/t, the yield required by a feed wheat is 9.6t/ha. This assumes higher quality grades are achieved in the milling wheat. The same applies to durum in reverse: if durum attracts a $50 price premium over milling wheat, then it would only need to yield 6.2t/ha to match the gross margin of a milling wheat at 8t/ha. These yields have been achieved under irrigation in 2020 and 2021. This may be a more profitable system than chasing the extra yields of feed wheat under irrigation.

Figure 2. Relationship between the grain yield of feed cereals and quality grades required to achieve similar gross margin returns at different feed delivery price spreads (assuming quality delivery price is $300/t).

Barley is a different story, as high yields and malt can be achieved in spring barley. However, introduction of higher potential winter feed barley cultivars could raise yield expectations. The price spread is lower between feed and malt barley ($20–$25) than feed and milling wheat. If 8t/ha of malt barley was achieved with a price spread of $25 over feed, then an additional 0.7t/ha (or 8.7t/ha) of feed barley is required to provide an equal gross margin. This is an important comparison because, for the first time, winter barley has now exceeded 10t/ha under dryland conditions (Table 4). Yields of 10.4t/ha were achieved in six row winter Pixel and 9.7t/ha in two row winters in the Southern HRZ, while Planet achieved 8.0t/ha from the same sowing date and 8.15t/ha from a later more optimal sowing date (yields not shown). Planet barley remains the benchmark cultivar for achieving high yields across all higher production environments. The key limitation to Planet is poor disease resistance.

Table 4: Grain yield (t/ha) and variety type evaluated under high yielding management conditions at Millicent in SA from early sowing 20211.

¹High yielding management conditions include a robust fungicide strategy, plant growth regulators and extra N described in the flow diagram in Figure 3. ²Lines are experimental and yet to be commercialised in Australia or receive a quality classification.

Feed winter barley is yet to achieve the same adoption as feed winter wheats

European introductions have demonstrated superior disease resistance to all spring cultivars, however, they grow too tall and are more prone to yield losses from lodging, head loss, and grain shattering. These production constraints can be managed with principles of canopy management in both contrasting cultivar types, highlighting the importance of disease resistance and fungicide lessons presented in the HYC wheat data below.

The summary of two wet seasons (three experiments) at Millicent SA, and Gnarwarre Vic of earlier sowing is below (Figure 3). A key finding was that the addition of an SDHI fungicide in the susceptible cultivar Planet increased yield by 1.2t/ha (6.1–7.3t/ha) irrespective of any other management factor. Whereas in the winter barley, yields were 6.6 and 6.7t/ha under standard and increased disease management, respectively. The addition of plant growth regulators or defoliation by grazing, or an extra 80kg of applied N did not increase yield and demonstrates in the barley variety Planet, disease management is the number one factor to achieve high yields.

In winter barley, the use of plant growth regulators (PGRs) to reduce height, lodging and head loss increased yield and was more important than extra fungicide applications alone, however in combination, they both increased yield. Under standard management, grain yield increased by 0.4t/ha (6.6–7.0t/ha) with the application of a PGR, whereas the more robust fungicide strategy did not increase yield unless it was combined with the PGR, and then increased yield by 0.7t/ha (6.6–7.3t/ha). Grazing or extra N did not further increase yield.

Figure 3. Mean yields and response to canopy management factors: fungicide application, plant growth regulators (PGR), nitrogen and grazing in two contrasting barley cultivars across three earlier sown experiments (~20 April) in the HRZ of SA, Vic (2020/2021).

Definitions of management factors:

¹Standard Management Control – 2 x cheaper foliar fungicide propiconazole (Tilt® 250 EC at 500mL/ha) @GS31 and tebuconazole (Folicur® 430 SC 290mL/ha) @GS39-49. Nitrogen managed for 8t/ha yield potential.

²Increased disease management – Systiva® seed treatment, 2 x foliar fungicides including QoI (strobilurin) & SDHI combinations with DMIs) with third fungicide if required.

^3,4Plant growth regulation (PGR) (Moddus® Evo 200mL/ha @GS30 & Moddus Evo 200mL/ha @GS33-37).

⁵Extra applied nitrogen (N) = Additional 80 units (kg of N) applied at GS31.

⁶Defoliation = simulated grazing @GS16 and GS30 or before Aug 15 in winters.

All other inputs of insecticides and herbicides were standard across the trial. Timings of PGRs and fungicides were adjusted to take account of the differences in spring and winter barley phenology (development).

Disease management in better seasons is essential with higher yield potential and in wheat and barley cultivars of poorer disease resistance. Irrespective of the medium or high rainfall zone (M-HRZ), it is crucial growers and advisers consider disease management as one of the most important components of growing high yielding cereal crops in seasons with higher yield potential as highlighted in barley above.

The other important lessons for the wetter seasons from these and adjacent experiments on the Hyper Yielding Crop centres will not be discussed here in great detail but have demonstrated in wheat and barley that:

• fertile soils in the HRZ limit the ability to manage yield and early biomass production with applied nitrogen in wetter environments — other techniques such as PGRs, cultivars and fungicides are more important for active management in the critical period
• canopy management benefits extend beyond the growing season – disease control and the combined application of PGRs and timely harvest ensures pre-harvest yield losses are reduced, particularly in barley (for example, head loss and brackling)
• waterlogging tolerance of barley compared to wheat is poor in wetter seasons, however earlier sowing of slow developing cultivars increases the chances of improved yield recovery post-waterlogging.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the investment of the GRDC, the author would like to thank them for their continued support. FAR Australia gratefully acknowledges the support of all of its research and extension partners in Hyper Yielding Crops project. These are CSIRO, the Department of Primary Industries and Regional Development (DPIRD) in WA, Brill Ag, Southern Farming Systems (SFS), Techcrop, the Centre for eResearch and Digital Innovation (CeRDI) at Federation University Australia, MacKillop Farm Management Group (MFMG), Riverine Plains Inc and Stirling to Coast Farmers. We would also like to thank our host growers in each state. FAR Australia gratefully acknowledges the collaboration of Irrigated Cropping Council and NSW DPI with this component of the Optimising Irrigated Grains project. We would also like to acknowledge Southern Growers Inc for providing and hosting the FAR Australia Finley Irrigated Research Centre.

Contact details

Kenton Porker
FAR Australia
Shed 2/63 Holder Rd, Bannockburn VIC 3331
08 5266 1290 /0403 617 501
kenton.porker@faraustralia.com.au
@far_australia

Nick Poole
FAR Australia
Shed 2/63 Holder Rd, Bannockburn VIC 3331
nick.poole@faraustralia.com.au
@far_australia

Tom Price
FAR Australia
Shed 2/63 Holder Rd, Bannockburn VIC 3331
tom.price@faraustralia.com.au
@far_australia

Rohan Brill
Brill Ag
rohan@brillag.com.au

Ben Morris
0421987486
ben.morris@faraustralia.com.au