Plant density and N response of selected wheat varieties at East Koorda 2015 trial report

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In a high yield potential season, seeding wheat at 60kg/ha gave a higher yield and gross margin than seeding at 30kg/ha; but there was no further benefit in going to 90kg/ha. The trial site had low nitrogen levels at seeding but a high yield potential due to autumn and winter rains. Wheat yields and protein increased with 50kg/ha of added nitrogen. Given grain protein was very low overall, it is reasonable to assume that the wheat crop would have responded to even higher nitrogen rates in similar seasons.


The challenge in low rainfall regions is to understand the influence of management inputs on the expression of genetic difference between varieties. Growers in low rainfall environment are focusings on dry sowing technologies to enable timely seeding of a proportion of their cropping program. A better understanding of how tactical decisions influence varietal performance in low rainfall regions will build confidence in decision making at seeding and throughout the season.


To quantify the nitrogen and crop density responses of current wheat varieties in a low rainfall cropping environment, and their interaction.

Trial details

Table 1 Trial details of wheat agronomy trial at East Koorda
Property East Koorda
Soil type

Depth (cm): 0-10
pH (CaCl2): 5.4
Soil mineral N (mg/kg): 14


Depth (cm): 10-20
pH (CaCl2): 5.5
Soil mineral N (mg/kg): 6


Depth (cm): 20-30
pH (CaCl2): 5.9
Soil mineral N (mg/kg): 5


Depth (cm): 30-40
pH (CaCl2): 6.3
Soil mineral N (mg/kg): 7


Total N in top 40cm: 36kg/ha

Crop Wheat
Paddock rotation 2014 - grassy pasture, 2013 - Emu Rock wheat, 2012 - Telfer TT canola, 2011 - wheat

Six wheat cultivars (Calingiri, Corack, Emu Rock, Mace, Magenta, Wyalkatchem) × four N rates (0, 10, 30, 50kg/ha) × three seeding rates (target densities 60, 120, 180plants/m2).

N rates were applied as 10kg N/ha at seeding with an additional 20 or 40kg N/ha as Flexi-N at mid-tillering (23 June) to give the appropriate rate.

Seed rates were chosen to give the target densities on the basis of seed size and germination percentage, but approximately 30, 60, and 90kg/ha to give 60, 120, and 180 plants/m2 respectively.

Replicates Three and plot size of 10m x 1.54.
Sowing date 13 May 2015
Seeding rate See treatments
Fertiliser (kg/ha) 120kg/ha Super CMZ at seeding
Rainfall 225mm (141.5mm in February, March, April)


The yield potential at this site in 2015 was 3.75t/ha: assuming 30% of summer rainfall is available for the crop, 80mm is lost by soil surface evaporation and a transpiration efficiency of 20kg/ha/mm. All cultivars achieved this potential at the highest N rate and some exceeded it. Variety, seed rate and nitrogen rate all had significant effects on grain yield, but there were no significant interactions between any of these factors. Grain protein only responded to N rate; however, protein levels were low even with 50kg/ha of applied N. Screenings were low, but there were significant differences between cultivars, with Emu Rock and Magenta being higher than the others. Screenings did not respond to N rate or density. Hectolitre weight was high, it differed between cultivars (Corack and Emu Rock were highest) and declined slightly with increasing N rate, but this effect was very small.

Calingiri did not yield as well as the other cultivars and its gross margin was lower. However, statistical analysis did not show a significant difference in gross margin between cultivars. Gross margins were calculated using a price of $270/tonne for ASW1 and production costs ranging from $252-364/ha depending on fertilizer application and seeding rate. Increasing N rate from nil to 30kg/ha increased gross margin by $99/ha on average; increasing N rate to 50kg/ha increased gross margin by a further $17/ha. Increasing density from 60-120plants/m2 also increased gross margin by $39/ha, but increasing density to 180 plants/m2 did not lead to any additional increase.


Even though 2015 was not a low rainfall season at north-east Koorda, these results are still relevant to questions about the viability of sowing dry and/or early in low rainfall environments. In fact, spring at this site was dry: there was only 3.5mm of rain in September and none in October. The density responses suggest that 60plants/m2 (about 30kg/ha) was too low for this season, but there was little advantage in increasing density from 120-180 plants/m2 (60-90kg/ha) even in this high yield potential season. This site had low initial soil N and (with organic carbon at 0.7% in the top 10cm) limited capacity to provide N by mineralisation. There was a strong response to applied N and (given the very low grain protein levels) it is likely that there would have been additional responses to the application of N at higher rates than tested. The highest yielding treatment Corack with 50kg N/ha, had the equivalent of 61kg N/ha in the grain; thus soil mineral N (and not fertilizer N alone) must also have been needed to account for grain protein and N in the straw (not measured).


The Storer family for allowing us to conduct this trial on their farm, Matt Willis (Elders Wyalkatchem) for helping us find the site, Shari Dougall and Bruce Thorpe (DAFWA Wongan Hills) for managing the trial, Bruce Haig (DAFWA Northam) for making the measurements and Grain Crop Agronomy Reference group (managed by GRDC) for their support with research development in 2015.

This research is a component of the Tactical wheat agronomy for the west (DAW00249) project funded by GRDC and DAFWA.

Contact information


Christine Zaicou-Kunesch
Bob French