Irrigated wheat agronomy x variety trials 2014 Trial Update

Take home messages

Due to cool spring conditions, high yields were readily achieved in 2014. The highest yields in our irrigated trials were slightly under 10 t/ha at Spring Ridge, and above 8 t/ha at Narrabri.

The new varieties Cobra and Trojan did well in their first year of testing in the northern region, being the highest yielding varieties in most trials and having high levels of lodging resistance.

Suntop showed significantly better lodging resistance in 2014 than we observed in preliminary trials in the 2013 season, and also had consistently high yields across all 2014 experiments.

Wallup, Lancer and Mitch all lodged to a greater extent in 2014 than observed in previous seasons, but are still considered acceptable for irrigated wheat growing when canopy management  strategies are used to reduce lodging risk.

Introduction

In response to increased interest in irrigated grains production, GRDC has funded the ‘Better Irrigated Wheat Agronomy’ project which is running experiments from 2012-2016. The project aims to improve agronomic recommendations to increase yield and decrease lodging risk in irrigated wheat, although project results are also relevant to dryland growers in high yielding districts.

This paper is a short update on selected variety performance results from the 2014 season. Detailed agronomic results will be presented at future GRDC Updates after testing has been conducted in additional seasons.

Trial program, 2014

In the first two years of the project (2012-2013), the trials were designed to test a wide range of varieties under different agronomic conditions. In 2014 we began more detailed testing on a smaller group of varieties. It is important to note that the varieties used in these experiments are protected by Plant Breeders Rights legislation within Australia.

The trials discussed in this paper were conducted at Spring Ridge, Narrabri and Emerald. All trials were managed to be pest and disease free through regular application of fungicides and insecticides (for aphids) where appropriate. While all trials were intended to be fully irrigated, some short term water deficits were experienced at Emerald and Narrabri that probably limited yield potential.

Results & discussion points

Cautionary notes:

The performance of agronomic treatments and varieties varies between locations and years. New agronomy or varieties should be tested on a small scale to ensure they are suitable for different locations and farming practices, as results from the trials reported in this paper may not be repeated at different locations or in different years. Additionally, some of the varieties that performed well are not on the recommended list for the Northern Region so it is important to ensure such varieties can be marketed before choosing to sow them. Finally, fungicides were used to control diseases in all trials as our aim was to test for yield potential in the absence of disease pressures. The performance of some varieties in these trials could be quite different in an environment/year with high disease pressure if fungicides are not used.

Season conditions in 2014

The 2014 season was quite different to 2013 (which was warm and dry and had low yield potential). The cooler conditions for much of 2014 meant that yield potential was higher, as crops received much more radiation per unit of thermal time. Frost was not considered to have had an effect on yield in any of the experiments.

Unfortunately all the trials reported in this paper ended up having high levels of N at sowing, and did not test variety performance under our preferred ‘best-practice’ N regimes which would normally induce N stress during late tillering. Although two of the fields (Narrabri and Spring Ridge) were soil tested prior to sowing and had approximately 70 kg/ha of N available (the normal N target for inducing a mild N stress), the crops showed no N stress during tillering or stem elongation. So while ‘delayed N’ treatments were still conducted at each location, the treatments did not represent the best practice for in-crop N application. N regime did not have a significant effect on yield or lodging at Emerald or Narrabri, and had inconsistent effects on yield and lodging at Spring Ridge.

Subsequent investigation revealed that the Spring Ridge site had high soil fertility (organic carbon of 2.3%), and a retest of soil N just prior to sowing came back at 115 kg N/ha, so it is probable that the site experienced 45 kg/ha of N mineralisation in the 3 months between soil tests (and possibly experienced further mineralisation post-sowing). At Narrabri the field was sown to Faba beans in 2013 and it appears that the legume stubble may have mineralised very rapidly under irrigation to release additional N. The Emerald trial area had been prepared by using a forage crop to reduce N levels, but soil N was extremely high prior to the forage crop and N levels were only reduced to approximately 150 kg N/ha. Due to the lack of N response in these experiments, we will be devising new N regimes for high fertility paddocks in future experiments that involve smaller and later applications of N.

Narrabri Trial

The data from Narrabri was interesting (Figure 1). Earlier sowing is often considered by researchers to have higher yield potential in dryland conditions, if frost can be avoided. However our data shows the opposite in this high yielding irrigated trial. As we had anticipated lodging was worse for the earlier sowing date, and the only varieties that yielded well on both sowing dates were the more lodging resistant varieties (Figure 1).

Most of the varieties yielded close to 8 t/ha on the late sowing date at Narrabri. The more lodging resistant varieties that achieved these yields on the early sowing date as well were: Cobra, Crusader, Livingston, Merinda, Mitch, Sentinel, Suntop, Trojan and Wallup (Figure 1).

Figure 1. (a) Yield and (b) lodging during grain filling, for 18 varieties in the irrigated wheat trial at Narrabri in 2014.

Notes on interpreting data for Emerald and Spring Ridge

At Emerald and Spring Ridge, lodging in the first few weeks after flowering followed the same trend as Narrabri, with more lodging observed in the early sown experiment than for the equivalent growth stages in the late sown trial. However these results changed (shown for Emerald in Figure 2) after significant lodging events (i.e. storms) that occurred during grain filling. There are several reasons why this may have occurred.

This trend may be related to the irrigation infrastructure at these sites, which required both experiments to be irrigated simultaneously with the same amount of irrigation. The experiment sown on the second sowing date would have used less water due to its delayed development, and potentially had wetter soil around the surface roots prior to each irrigation event. Therefore varieties sown on the late sowing date could have been more prone to root-lodging than plots sown on the early sowing date on the day of the storms, simply due to the irrigation scheduling and the condition of the soil. This was less of a problem at Narrabri where we were able to water the sowing dates separately.

Figure 2. Mean lodging progression across all plots for the early and late sowing dates at Emerald in 2014. Timing of lodging is expressed in relation to anthesis, therefore the lodging event in week 5 for the early sowing date was the same event that caused lodging in week 3 of the late sowing date.

Alternatively, because the lodging events occurred at a later growth stage for the early sowing date, the stems of these plots may have stiffened prior to the lodging event, and become more resistant to lodging. At Emerald, the trend could also have been related to the lower plant population established on the first sowing date, which would have decreased its lodging susceptibility in relation to the late sowing date. Finally, the relative timing of the large lodging events also means that a longer period of grain filling was affected by lodging for plots sown on the late sowing date. These results have prompted us to consider a partial redesign of the trial program in 2015 to better understand these trends.

Summary of Results – Emerald

The data for Emerald are presented in Figure 3. As we mentioned in the previous section, the late sowing date was more heavily affected by the lodging event during grain filling, and had lower yields than the early sowing date. The low yields of the late sowing date may not have been solely due to lodging, but might also have been caused by hotter temperatures experienced during grain filling.

Of the varieties at Emerald, a number of varieties were similarly high yielding (6-7 t/ha) for both sowing dates (Figure 3), and of these some lodged less than others. The consistently high yielding, low lodging varieties at Emerald were Caparoi, Cobra, Merinda, Sentinel, Suntop and Wallup. Mitch and Kennedy also yielded similarly but lodged a little more than the aforementioned varieties (Figure 3).

Figure 3. (a) Yield and (b) lodging during grain filling, for 18 varieties in the irrigated wheat trial at Emerald in 2014.

Summary of Results – Spring Ridge

The data for Spring Ridge are presented in Figure 4, and are a little more complicated than those presented for Emerald and Narrabri. At Spring Ridge, statistical analysis revealed significant 3-way interaction between varieties, sowing dates and N regimes. Therefore we have presented 4 lines of data, one for each combination of N regime x sowing date, across all varieties. Additionally, two graphs have been presented for lodging, one that encompasses lodging for the first 2/3 of grain filling (Figure 4b -which excludes the large, late lodging event that affected the later sowing date more than the earlier sowing date), and another that represents lodging for the whole of grain filling (Figure 4c).

In Figure 4b, it can be seen that the late sown treatments were generally lodging less than the early sown treatments over the equivalent period of grain filling (approximately 5 weeks). But after the severe late lodging event, the late sown treatments became more heavily lodged than the early sown treatments (Figure 4c) for a number of varieties (but not all varieties).

As previously discussed, the delayed N treatments that were used didn’t represent best practice for in-crop N application, as soil N supply during tillering was ultimately much higher than crop demand. It was still interesting though that on the early sowing date, the in-crop N treatments tended to have more lodging and lower yields than the sowing N treatments. However, the opposite was observed on the late sowing date where in-crop N application tended to yield better and have less lodging! However, these trends didn’t apply to every variety. As with the sowing date comparisons, these results have prompted us to consider modifications to our trial designs in 2015 to see if we can better understand some of the trends that were observed in 2014.

Figure 4. (a) Yield, (b) lodging during the first 5 weeks of grain filling, and (c) lodging during the entire grain filling period for 18 varieties in the irrigated wheat trial at Spring Ridge in 2014. The early sown treatments were sown on May 19^th, and the late sown treatments were sown on June 11^th.

We suspect that this particular trend may be related to our application of a large, single dose of in-crop N to a field already high in N, perhaps interacting with soil conditions at the time of application that could also have affected the rate of N uptake or N losses.

Interestingly, a section of the early sown experiment was observed to have reduced canopy size, which was particularly noticeable in a number of delayed N plots. This was attributed to mild N stress potentially caused by spatial variation in soil residual N levels. Within this area yields were similar to the rest of the experiment, but lodging was reduced by nearly 50% (data not shown). While this was possibly a good demonstration of how low soil N levels can reduce lodging risk, we cannot rule out the possibility that another unknown factor was involved.

Although there was significant interaction between varieties and agronomic treatments, broad trends were still evident in varietal performance at Spring Ridge (Figure 4). Trojan achieved the highest yields, very nearly yielding 10 t/ha in two of the four agronomic treatments. Cobra and Sentinel achieved consistently high yields of approximately 9 t/ha for all 4 agronomic treatments, while Mitch, Bellaroi and Suntop were not far behind them, consistently yielding between 8 and 9 t/ha across the agronomic treatments. Lancer, Merinda, Livingston, Wallup and Caparoi also performed reasonably well. In general, the highest yielding varieties were those that lodged the least.

Summary & conclusions

These results from irrigated variety trials in 2014 provide up-to-date data on the most lodging resistant, high yielding germplasm available to northern region growers. A summary of all trial results is listed in Table 1, which presents the difference between variety mean yield and trial mean yield for each variety in each experiment. Updated variety lodging resistance ratings (developed from project experiments run from 2012-2014) are listed in Table 2.

The varieties Cobra and Trojan were sourced from southern Australia and were quite promising. Cobra yielded more than 5% above the trial mean yield in each experiment, and Trojan yielded more than 5% above the trial mean yield in seven out of the eight experiments (Table 1). It should be remembered however that neither of these varieties is being promoted or marketed in the Northern Region at this stage, and lodging ratings are provisional as data has only been collected from one year. Both of these varieties have relatively restrictive quality classifications in the Northern Zone, with Cobra having a default APW classification, and Trojan having a default ASW classification.

Mitch (AH), Lancer (APH) and Wallup (APH) all showed that they are not quite as lodging resistant as we thought after the first two years of testing, but are still considered acceptable for irrigated wheat growing. Their lodging ratings have been downgraded slightly from ‘R-MR’ to ‘MR’. On the other hand Suntop^* (APH) was seen to have better levels of lodging resistance in 2014 than we observed in preliminary trials in 2013, and its rating has now been upgraded to MR. Suntop was also the most consistently high yielding APH variety, yielding more than 5% above the trial mean in each of the 2014 experiments. However this was the first year of widespread testing for Suntop in our experiments, and its performance is still considered provisional. Mitch and Sentinel (ASW) were also consistently high yielding across experiments.

With the identification of more lodging resistant varieties in the last two years, Kennedy and Crusader are no longer the only ‘safe bet’ varieties that we identified in our initial trials 4-5 years ago. Kennedy in particular does not seem to perform particularly well in the more southern locations and is more susceptible to lodging than most other varieties in these trials. However it still performs well at Emerald and Gatton (yields of 9.3 t/ha were achieved at one of our Gatton trials in 2014).

Table 1.  Percent difference to trial mean yield for all varieties in each experiment in 2014

Highlighted cells indicate variety mean yield >10% above trial mean yield

Shaded cells indicate variety mean yield >5% above trial mean yield

Table 2. Lodging ratings for varieties assessed in the 2014 irrigated trials, as rated using combined results from the 2012-2014 trials of the Better Irrigated Wheat Agronomy Project. Varieties listed in the 2015 QLD Wheat Variety Guide have the same lodging ratings as presented here. Varieties listed within the 2015 NSW Wheat Variety Guide may have slightly different ratings due to differences in varietal performance between northern and southern NSW.

R-MR = Resistant to Moderately Resistant                                     MR = Moderately Resistant  

MR-MS = Moderately Resistant to Moderately Susceptible           MS- Moderately Susceptible

MS-S = Moderately Susceptible to Susceptible                               S = Susceptible

** = Preliminary rating based on one year of trial data

The results of our sowing date comparisons were not as consistent as we had expected, with the later sowing date sometimes having more lodging than the early sowing date. Further testing in 2015 may shed more light on this trend.

Finally, it should be remembered that variety choice is just one of the agronomic options available for reducing lodging risk. When lodging risk is high, a number of agronomic management options should be used to reduce lodging risk. Other options have been reported in previous GRDC updates and irrigated wheat fact sheets (see ‘further reading’ section below). These include using appropriate plant populations (of approximately 100 plants/m² on irrigation beds), in-crop N application, and the use of a registered plant growth regulant (PGR) such as chlormequat chloride. Avoiding irrigation shortly before forecast rain events late in the season may also be advisable if sufficient soil water is held in deeper depth layers.

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, and the authors would like to thank them for their continued support. We also thank farm and technical staff at the DAFFQ Emerald Research Farm, and the University of Sydney’s Plant Breeding Institute (Narrabri) for their assistance in managing these trials, along with Angus Murchison of Spring Ridge for hosting one of the trials.

Further Reading (available from the GRDC website at www.grdc.com.au)

Fact Sheet (Northern Region): ‘Reducing lodging Risk in irrigated wheat’

GRDC Goondiwindi Update Paper (2012) by Peake et al. “Agronomy for high yielding cereal environments: varieties, agronomic strategies and case studies”

GRDC Goondiwindi Update Paper (2013) by Peake et al. “Beyond 8 t/ha: varieties and agronomy for maximising irrigated wheat yields in the northern region”

Contact details

Allan Peake
CSIRO Agriculture Flagship, 203 Tor St, Toowoomba.
Ph: 07 4688 1137
Email: allan.peake@csiro.au

Reviewed by

Douglas Lush, DAFFQ