The trial was sown 22 April and again on May 6 2024.

Pre-irrigation occurred in early April saw sowing occur into good soil moisture and emergence was even across the trial.

Eight wheat varieties, consisting of two winter (BigRed and DS Bennett), One very slow spring (RGT Zanzibar), one slow spring (Valiant CL), three mid-slow spring (Coota, Genie and Rockstar) and one mid maturity spring (Kingston) were sown ‘early’ on April 22 and again on May 6.

Grain yields were compared and, as a trend, unless the variety had a winter vernalisation requirement or was very slow to develop, early sowing had an average yield penalty of 1.4 t/ha, with a range of 0 to 2.1 t/ha.

Contributing to this yield penalty was the disease resistance of the varieties, which saw varieties more susceptible to septoria (septoria tritici blotch) showing a higher degree of infection and leaf loss from the earlier sowing.

The trial aims to compare the benefits and challenges of pre-irrigation (where the site is irrigated prior to sowing and allowed to dry until soil moisture is suitable for sowing). Pre-irrigation allows timely sowing and a full moisture profile for the developing crop that should provide sufficient moisture for the crop until spring when the irrigation system restarts. However, it is not without its risks as above average autumn rainfall can delay or abort sowing altogether due to being too wet. A full soil profile going into winter can also risk waterlogging if winter rainfall is above average. Conversely, not pre-irrigating relies on rainfall for sowing and replenishing the soil profile to enable winter crop growth, exacerbated by the heavy clay soils that absorb a large proportion of small rainfall events.

The ‘Pre-irrigation’ site was pre-irrigated in early April and the site sown on May 2nd to 3 wheat varieties (slow, mid and quick maturity), 2 barley varieties (quick and mid-slow maturity), 2 canola varieties (early-mid and mid maturity) and 1 faba bean variety.

The ‘Not pre-irrigated’ site was sown on May 15th with the same crops and varieties as above after a 15mm rainfall event, but emergence has been slow due to rapid drying of the site and lack of follow-up rain until May 31st.

Early sowing changed the disease profile expressed by some varieties - earlier sown showed more damage due to septoria

Some of the early sown varieties that may have a yield benefit from early sowing (extended vegetative period due to winter habit/vernalisation) also bring some strong foliar disease resistance genes.

Early sowing can help spread the work load at sowing.

Need to have the right maturity when early sowing to match flowering window and that information is sometimes lacking as demonstrated by some varieties flowering 3-4 weeks earlier than the target date. 

Dry sowing is not an option when irrigation water is available.

Early sowing of fabas and watering up is a viable option for crop establishment but yield and harvestability yet to be assessed.

Pre-irrigation plots look a lot better than no pre-irrigation and relying on the season break due to better establishment and 1 month difference in crop emergence.

Pre-irrigation does still run the risk of waterlogging in sensitive crop types even in an 'average' season.

Irrigation brings some advantages that dryland growers don’t have. Irrigators can pre-irrigate so that we have control (not total though) over sowing date.

Early sowing isn’t without its own risks – frost, particularly if you are sowing your main season wheat earlier than optimal, changes in disease management and reduced yield potential due to earlier crop development are all possible issues to be managed.

Frost – unless your variety has the capacity to adapt its flowering date, then sowing your main season wheat early increases the risk of frost through flowering too early. Having a variety with some degree of vernalisation does help delay flowering but many varieties have little requirement for vernalisation and those that do tend to be the longer season wheats.

A change from the normal sowing window can alter disease management strategies, which may mean changes to timing or products with a different disease control spectrum.

The thirty-day period leading up to flowering, called the critical period, sets the crop yield potential. If we sow early, and flower early, then yield potential is reduced thanks to reduced sunlight intensity and daylength. That is, if the target flowering date is the end of September and early sowing brings this forward, then the 30 day period prior to flowering is now occurring in a time of shorter days and with less solar radiation intensity. As an aside, moisture stress during this period also reduces yield and so make sure the crop has adequate moisture through this period. We have previously said “booting’ as the critical

phase but in reality, it is a longer period than this as demonstrated by our Smarter Irrigation for Profit work when irrigation at booting had already induced stress and this was reflected in a loss of yield.

The other side of the coin is late sowing. Waiting for the break rather than pre-irrigating can be a risky strategy, with the risk increasing if sowing canola and faba beans. These crops do not have the ability to compensate for lack of winter growth like the cereals. Added to this risk is being in irrigation regions where water is unavailable in the winter and the crop may end up in a winter ‘drought’, losing yield potential while waiting for the irrigation season to open.

IFN trial results

The IFN trials for this project addressed two themes – comparison between ‘early’ and ‘on time’ sowing dates and also looked at the effect of pre-irrigation, not so much as allowing early sowing, but to compare ‘on time sowing’ with relying on rainfall.

Time of Sowing Comparison

Disease control was an issue in the two years of the project. In 2024, septoria was a problem that was worse in some of the varieties that were sown earlier.

 In 2023, where stripe rust was the main disease, there was some benefit to early sowing as the earlier seeded plots were more advanced and had developed their adult plant resistance earlier before stripe rust became evident.

Table 1 shows the results of the trials, comparing the overall trial average, yields from two varieties that were common to all 4 trials and the average yield of 8 varieties common to the two trials in 2024.

Table 1: Comparison of the ‘Early’ and ‘On time’ trial yields (t/ha)

Statistical analysis of this data indicates there was no significant difference between the yields from the 2023 sowings (p=0.180) there was in 2024 where the ‘early’ suffered a yield penalty (p=0.048, lsd=0.891 t)

Pre-irrigation as a de-risking strategy

In 2024, IFN re-visited what was called our ‘plus or minus trial. In 2018 we conducted a trial where we had different irrigation strategies that looked at the effect of plus or minus pre-irrigation coupled with a 1 or 2 spring irrigation strategy.

A quick summary of both 2018 and 2024 results was:

• While the most efficient use of water was from the first spring irrigation, you need a crop that is capable of responding.
• Canola and faba beans benefited from pre-irrigation through timely sowing and adequate moisture through the winter provided conditions that allowed the crop to grow sufficiently to respond while the ‘no pre-irrigation’ had insufficient growth and was a poor competitor with weeds.
• The cereals showed more resilience to dry winter conditions and could respond to spring irrigation.
• Barley yields in 2024 were higher with no pre-irrigation due to mild winter waterlogging thanks to pre-irrigation plus rainfall.
• The maturity of the variety played an important part in how a variety performed under spring irrigation. In 2018, quick maturing varieties fared worse due to them being too advanced when able to be irrigated in spring – tillers numbers were set and irrigation simply resulted in bigger grains. Longer season varieties or late emergence due to late rain and no pre-irrigation saw varieties able to respond to spring irrigation due to tiller production and/or survival and hence yield.

The 2024 cereal trial ‘pre-irrigation’ treatments were pre-irrigated April 8^th and sown May 2^nd. The ‘no pre’ trials were sown May 15^th but did not emerge until June 11^th

2024 wheat yields were reasonably consistent across the treatments; however, the longer season wheat had the highest yield. This result was similar to the 2018 trial where the quicker maturing cereals were too advanced by the time irrigation became available in the spring while the later maturing cereals were still vegetative enough to respond to spring irrigation with increased tillering or tiller survival. In recent conversations at the IFN 2024 Winter Trials Results Day, the prevailing opinion was that you get the best response to irrigation in the spring but you must have a crop that is capable of responding.

Table 2a: Wheat yield results (t/ha)

Yield figures with different superscripts are statistically different.

Rabbits removed ‘No pre + 1’. N management was impacted by the dry July-August conditions

2024 barley yields were a slightly different result to the wheat in that the not pre-irrigated results were better than those from pre-irrigated treatments. Delayed sowing and emergence in June thanks to the lack of rain in May saw the barley plants still vegetative when spring irrigation became available and so went on the yield quite well. The pre-irrigated barley suffered from mild waterlogging in June and then lack of nitrogen in late winter thanks to limited opportunities to topdress.

Table 2b: Barley yield results (t/ha)

Yield figures with different superscripts are statistically different

Summary

Don’t forget we still have a preferred flowering window! Wrong variety = wrong timings for development

Disease management may have to be adjusted if early seeding does happen – and knowing the current disease ratings of your variety is essential.

Pre-irrigation or watering up canola and faba beans enabling sowing on time and moisture for winter is the best strategy, particularly in the western part of the irrigation region.

The cereals are more flexible when making the pre-irrigation or not decision and can yield well if they are not too advanced/able to respond when irrigation happens in the spring. This can be achieved by either using a variety that has a degree of late maturity or delay sowing a little (which is not without its risk as well). But then again, farming without risk is farming unlived.