Key messages

• Nitrogen (N)
• Illabo, Denison and Rockstar sown on 8 April yielded 5.2 to 5.6 t/ha.
• All varieties had an increase in grain yield and protein from applied nitrogen fertiliser.
• Water use efficiency (WUE) increased with the higher rates of applied nitrogen.
• The variation in crop phenology between the longest (Illabo) and shortest (Rockstar) varieties did not have a significant impact on WUE in this trial.

In 2021 the summer and early season rainfall prompted early sowing in many parts of the WA wheatbelt. Sowing earlier than the traditional May break makes use of summer moisture and may mean higher yields – if the right varieties are used. Longer growing varieties sown early (March/April) have demonstrated higher yields compared with typical spring wheats sown in the traditional window (May/June).

The varieties used were: 
• Illabo (AGT). A winter wheat variety with a vernalisation ‘cold’ requirement before entering into reproductive growth stages (APW/AH).
• Denison (AGT). A very long season spring wheat (APW). 
• Rockstar (Intergrain). A medium-long season spring wheat (APW/AHN).

This trial aims to provide some local data that will help growers assess their yield potential and N requirements.

Trial Details

Location                    Dalwallinu
Soil type                    Red brown alkaline clay
Paddock rotation     2019 chemical fallow, 2020 wheat, 2021 wheat
Sowing date              8/04/2021
Sowing rate               53 kg/ha Illabo, Denison and Rockstar wheat
Harvest Date             4/11/2021
Rainfall                       Dalwallinu Summer rainfall (November 2020 - March 2021) 148mm
(BOM)                         Growing season rainfall (April 2021 - October 2021) 331mm 

Table 1. Soil chemistry February 2021.

Treatments and Results 

Table 2. The effects of nitrogen (N) applications on grain yield, protein, nitrogen use efficiency (NUE) and water use efficiency (WUE) of Illabo, Denison and Rockstar wheat. 

Treatments 1 and 9 were sown with 97 kg/ha TSP; other treatments were sown with 100 kg/ha Agflow Boost
*NUE assumes 75% of N taken up is recovered in grain
** based on one third summer rainfall + GSR / grain yield
*** different letters beside treatment means denote significant differences between treatments (p<0.05)
Flexi-N (FN)

Results
With zero N applied, Illabo yielded about 1 t/ha lower than Rockstar.

With 180 kg N/ha applied, Illabo, Denison and Rockstar had similar yields (5.2 to 5.6 t/ha).

WUE increased in all varieties with the higher N rates.

Denison had the highest WUE of 15 kg/mm with 180N.

Illabo had the biggest increase in WUE, from 8 to 14 kg/mm, with the application of 96N. Adding further N (180N) did not increase WUE.

In Illabo, splitting Flexi-N between seeding (50 L/ha) and mid-tillering (50 L/ha) was more effective (higher yield, protein, NUE and WUE) than banding 100 L/ha at seeding.

In Rockstar, banding 100 L/ha Flexi-N at seeding with another 100 L/ha at early tillering was more effective (higher yield, NUE and WUE) than banding 50 L/ha at seeding with 150 L/ha at tillering.

Grain protein increased with the rate of N applied in all varieties.
The recovery of fertiliser N in the grain (NUE) was 30-40% in Illabo but less than 20% in Rockstar.

In Rockstar, screenings were 4-6% and hectolitre weights 79-81 kg/hL (data not shown). Neither were adversely affected by high N rates.

In Illabo, screenings were 2-3% and hectolitre weights 77-81 kg/hL (data not shown). Hectolitre weights were higher with increasing N supply.

In Denison, screenings were 3-4%; hectolitre weights 82-83 kg/hL (data not shown). Neither was adversely affected by high N rates.

Comments
The results from this trial indicate that winter wheats such as Illabo may have a higher requirement for N fertiliser than spring wheats such as Rockstar.

The variation in crop phenology between the longest (Illabo) and shortest (Rockstar) varieties did not have a significant impact on WUE observed in this trial.

The grain quality traits of screenings and hectolitre weights were not adversely affected by the high rates of N applied.

The importance of N in supporting grain protein levels in high yielding crops was also evident.