Matching phenology, environment and variety to optimise wheat yield

Take home messages

• Understanding temperature variance across farms/regions is essential for targeting optimum flowering windows for wheat.
• Matching varietal maturity to target optimum flowering dates for a given location is key to minimising both frost and heat stress.
• Generally, no one variety will maximise yield across the full planting window. Yield response for any particular maturity/variety will vary depending on time of sowing.

Introduction

Recommended sowing times for wheat varieties have been developed over many years of NVT testing to predict a optimum flowering window. It is reasonable to assume that if your sowing dates generally line up with your nearest NVT trial sites’ planting dates, then varietal flowering dates and yield response should be similar, all other factors being equal. Varieties selected for the NVT sowing dates are based on maturity length, and as such, not all tested varieties are included in both the main season and early sowing dates.

This however raises a question - if you were to receive planting rain, but your predicted ”optimum” sowing for your wheat variety window doesn’t open for another 2 - 4 weeks, could or should you plant anyway and what effect will this earlier sowing date have on days to flowering? Equally, what effect would this have on your yield potential? Conversely, if you don’t get a season break till very late in your planting window, can you still reasonably expect to get similar yields to the NVT trial data? How significant an effect will heat play during flowering and grain fill?

Background

The DAF research agronomy team has worked with NSW DPI in the Variety Specific Agronomy Package (VSAP) project in 2015 and 2016 looking at the effect of a range of agronomic triggers to optimise yield and grain quality. In 2017, a new project began with a more focused approach, mapping biomass accumulation and growth stage timing for multiple sowing times across the northern grains region. This new project, Optimising Grain Yield Potential in the Northern Grains Region (Winter Cereals) is a GRDC/NSWDPI Bilateral project led by NSWDPI in collaboration with DAF QLD.

In 2015 and 2016, eighteen varieties with a wide range of maturities were selected and planted on three or four sowing dates approximately a month apart from each other. All sowing dates had access to similar starting waters for that particular site, however once emerged the trials were treated as dryland through to maturity.

In 2017 the new project reduced the sowing window gap back from 30 days to 15 days with 30 varieties assessed. Eight trials were planted from Wagga to Emerald, all with the same times of sowing, to compare plant development across eight very different climatic regions.

Results

In 2015, three times of sowing (TOS) occurred with 18 varieties at each site. Sowing dates were spread one month apart to represent early, traditional and late planting windows for the regions the trials were located. For Emerald, dates selected were 15 April, 12 May and 9 June.  For the Goondiwindi site, target sowing dates were 27 April, 26 May & 8 June. The season in 2015 was very dry and daily maximum temperatures started to rise earlier than average at both sites. Tables 1 and 2 show average yield for each variety at each time of sowing and estimated days from planting to 50% anthesis. The season suited quick varieties at both locations, but also showed a significant decline in yield between each time of sowing.

In 2016, there were three times of sowing at Goondiwindi and four at Emerald; Tables 3 & 4 show the results for both trials. Sowing dates for Emerald were 16 March, 13 April, 11 May and 15 June 2016, while Goondiwindi TOS dates were 26 April, 24 May and 4 July.

2016 was a considerably milder and wetter season than 2015 for both sites and average yields reflect this. It must be noted that good in crop rainfall did not fall until the end of May, continuing through to mid-July for that season. This had a noticeable effect on time to anthesis for TOS 1 & 2 at Emerald, which were significantly quicker and more in line with 2015 days to anthesis, while the later TOS 3 and 4 were longer; in particular, TOS 3 did not show the yield drop off when compared to TOS 2 unlike the previous year.

Frost damage was observed, particularly during flowering for TOS 1 at the Goondiwindi site, as would be expected given the planting dates, but only some varieties were affected and none were completely lost as average yields indicate in Table 3. Temperatures did drop down below 2^oC at Emerald, no frost damage was observed.

Table 1. Goondiwindi site 2015 -  days to 50% anthesis and grain yield (standardised for moisture) for each of the three planting dates. Letters indicate significant difference (P=0.05) of yield between varieties within a TOS.

Table 2. Emerald site 2015 - Days to 50% anthesis and grain yield (standardised for moisture) for each of the three planting dates. Letters indicate significant difference (P=0.05) of yield between varieties within a TOS.

LSD w/i T (within a time of sowing (TOS) – ie two varieties compared with the same TOS): 361.7
LSD b/w T (between times of sowing – eg a yield in TOS 1 compared with a yield in TOS 3): 590.8

Table 3. Goondiwindi site 2016 - Days to 50% anthesis and grain yield (standardised for moisture) for each of the three planting dates. Letters indicate significant difference (P=0.05) of yield between varieties within a TOS.

l.s.d. w/i T: 508
l.s.d. b/w T: 574

Table 4. Emerald site 2016 - Days to 50% anthesis and grain yield (standardised for moisture) for each of the three planting dates. Letters indicate significant difference (P=0.05) of yield between varieties within a TOS.

l.s.d. w/i T: 394
l.s.d. b/w T: 411

Table 5. Emerald site 2017 - Days to 50% anthesis and grain yield (standardised for moisture) for each of the three planting dates. Letters indicate significant difference (P=0.05) of yield between varieties within a TOS.

l.s.d. w/i T: 366
l.s.d. b/w T: 355

The 2017 data in Table 5 doesn’t show a significant difference in yield unlike previous years and trials. As a site average, there was no significant difference in yield between TOS dates, however individual varieties like Mitch, Coolah, Cutlass, Sunmax and EGA Eaglehawk all show statistically significant declines in yield between TOS 1 and TOS 3. Most of these varieties are considered longer season varieties for the central Queensland (CQ) environment and highlight the difference a later planting date can make. Interestingly, none of the recognised quick varieties managed to yield significantly better in the later TOS 2 and 3, than the earlier planted TOS 1. This is despite the perception of being better suited sowing at a later date (mainly due to frost management concerns).

Analysis

The general trend across all locations has consistently been declining yield from the first TOS to the last. Excluding an exceptionally early (March) plant, generally the earlier the crop is planted within an accepted planting window, the higher the yield potential (baring frost damage). While frost is front of mind currently as a result of the exceptional frosts seen in 2017, heat stress must also be considered just as significant a threat to growers bottom line. When the data from Tables 1 to 5 is plotted against heat and cold risk charts generated with the CliMate application (climateapp.net.au) a TOS which target safer flowering periods can be identified.

Figure 1. Goondiwindi – 2015 Probability of heat and cold stress x flowering dates and achieved yield

Heat stress = >30^oC Cold Stress = <2^oC Risk - 1 in 10 Planting dates - 27th April, 26th May and 8th July 2015 (climateapp.net.au)

CliMate is a free application, which allows you to assess the likelihood of a predefined heat or cold stress event based on historical weather data for a given location. The weather database is extensive, so it is not too difficult to find regionally relevant data for your conditions. Winter cereals flowering in a temperature range lower than 30^oC and above 2^oC is generally considered as non-limiting to yield potential. When you overlay the flowering dates and yield achieved over the top of this chart, you can very quickly start to understand what factors may have contributed to yield decline during your flowering period.

Figure 1 shows the yield and flowering data from Goondiwindi in 2015 overlayed onto one of these graphs. The green bars show what period of year, (given a risk level of 1 in 10 years of exceeding the min or max temps) you could expect the preferred conditions described above. For Goondiwindi, it indicates that ideally flowering/grain fill should start from the last week of August to avoid an elevated frost, and conclude no later than the third week in September to avoid significant heat stress during flowering and grain fill. Figure 1 also shows that flowering dates for TOS 3 and even longer season varieties in TOS 2 were well into the elevated risk period for heat stress. TOS 1 in that particular year managed to avoid frost damage, hence why yields were so good despite flowering in an elevated frost risk period.

Figure 2. Goondiwindi – 2016 Probability of Heat and Cold Stress x Flowering Dates and Achieved Yield

Heat stress = >30^oC Cold Stress = <2^oC Risk - 1 in 10 Planting dates - 26th April, 24th May and 4th July 2015 (climateapp.net.au)

The 2016 season saw significantly higher yields but possibly a more traditional response to heat and cold stress. TOS 1 flowering dates were again within the elevated frost risk period, however this time frost did occur and yields suffered as a result. Again TOS 3 yields declined rapidly as the heat stress risk increased. Optimum yields for the site were achieved within the optimum flowering window.

For the Emerald site, significant differences in climate are revealed, as the dynamics of the graph change considerably. The risk of temps below 2^oC fall away to a level which it is not considered a likelihood with a 1 in 10 year risk profile. But the low heat stress period is a month shorter than that observed at Goondiwindi.

As with Goondiwindi, 2015 was a hot dry year and as expected, the earlier TOS performed as well as could be expected for the season. It is interesting to again observe that mid-season varieties performed the best for TOS 1. Quicker varieties yielded greater on average in TOS 1 compared to the 2^nd and 3^rd TOS. For TOS 2 and TOS 3 the quicks out yielded mid and longer season varieties.

2016 was a much milder season, but the site experienced prolonged hot conditions until the late May rain arrived. Thus TOS 1 in March struggled with temperatures in excess of 40°C during emergence and 30°C at flowering and grainfill. Comparatively, longer season TOS 2 varieties and all TOS 3 had mild, almost ideal flowering and grain fill conditions, hence the significant yield response difference from the 2015 TOS 3 date. Rain stopped in mid-July, so conditions returned back to a drier CQ winter/spring as can be seen by the significant yield drop for TOS 4 trying to flower as conditions quickly rose past the 30^oC heat stress threshold.

Figure 3. Emerald Research Facility 2015 & 2016 - Probability of Heat and Cold Stress x Flowering Dates and Yield

Heat stress = >30^oC Cold Stress = <2^oC Risk - 1 in 10

In spite of the nearly four month “optimum” for flowering and grain fill at this CQ site, the trend in yield x flowering response over the past three years now indicates that this window may not be as wide as it seems. To date, highest yields, have been achieved flowering between the 2^nd and 4^th weeks of June, which is exceptionally early, even for many in CQ. However, if the frost risk was understood and deemed acceptable, for a given region/client, then you would ideally be targeting a flowering date in that range.

Conclusion

Targeting an optimum flowering date is critical to maximise grain yield by balancing heat and frost risks. Selecting varieties with known and understood flowering dates, allows growers and agronomist to make more informed variety/maturity selections for future crops. As this data shows, days to flowering can vary significantly between locations and between planting dates, so observing and recording on-farm flowering dates from year to year could become a very useful management tool for your particular location in trying to optimise varietal selection.

Frost risk is a significant consideration, as 2017 showed us once again, however so too is heat stress. Growers and agronomist must be cautious not to take too conservative approach to frost mitigation, as chances are it will cost you significantly in yield also as a result of heat stress. Those considering planting very late in the traditional planting window with a high risk of flowing in heat stress conditions may actually be better off waiting a month or so and chasing a potentially more lucrative early summer crop instead.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC. The author would like to thank them for their continued support. We would also like to acknowledge and thank collaborators and co-operators over the past three years, who have allowed us to conduct on-farm trials across QLD. And to recognise the DAF Research Agronomy teams located in Emerald, Toowoomba and Goondiwindi for all the work that went into managing the trial programs over the past three years.

Contact details

Darren Aisthorpe
Department of Agriculture and Fisheries QLD
99 Hospital Rd. Emerald QLD 4720
Ph: 07 4991 0808
Mob: 0427 015 600
Email: Darren.aisthorpe@daf.qld.gov.au

Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.