1. Extra crop competition with weeds by increasing wheat seeding rate
Peter Newman

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The AHRI Communication Team (Peter Newman, Brogan Micallef & Lisa Mayer)

3. This trial by David Minkey, formerly of the Department of Agriculture, conducted at Merredin in the 90’s is a near perfect data set.
This trial shows that it is possible to improve competition with weeds either by reducing row spacing, increasing the seeding rate, or both.

4. 1999 - Mingenew More practical seeding rates & row spacings
Increasing competition reduces weed seed set
Little benefit in increasing seeding rate above 60 kg/ha
Panicles /m2
This trial by Peter Newman in 1999 has more practical seeding rates and row spacings and also shows that increasing competition reduces weed seed set.
The interesting thing here is that for wide row spacing there was little benefit in increasing wheat seeding rate above 60 kg/ha

5. 2012 – Mingenew Minus Sakura
Increasing the wheat seeding rate decreases ryegrass seed set in the absence of pre-emergent herbicide
This trial, conducted by Peter Newman while working for DAFWA with GRDC funding in 2012 shows the benefit of increasing the wheat seeding rate on ryegrass seed set in the absence of pre-emergent herbicide

6. 2012 – Mingenew Plus Sakura
Higher wheat seeding rates significantly reduced ryegrass seed set where Sakura was applied pre-sowing
The 2012 Mingenew trial also showed that herbicide plus competition gave a great result.
Higher wheat seeding rates significantly reduced ryegrass seed set where Sakura was applied pre-sowing

7. Many growers comment that high wheat seeding rates results in high wheat screenings levels (small grain).
However, these two trials and many more like them show that there is no impact of high wheat seeding rates on screenings

8. Binnu trial 2012 Wild radish
40 kg/ha
160 kg/ha
Impact of high wheat seeding rates on wild radish growth
The radish were present in a narrow, un-sprayed strip across the trial
This trial at Binnu by Peter Newman while working with DAFWA with GRDC funds shows the impact of high wheat seeding rates on wild radish growth.
The radish in this picture were present in a narrow, un-sprayed strip across the trial

9. Wheat & radish dry weight
Un-sprayed radish
High wheat seeding rates increased wheat biomass & decreased wild radish biomass
Graph depicts wheat and radish dry weight (13 Sept 2012)
The wild radish biomass data from the Binnu trial confirms what the pictures indicated.
For un-sprayed radish, high wheat seeding rates increased wheat biomass and decreased wild radish biomass

10. Wheat yield
Problem with high seeding rates is often no response in wheat yield
40 kg/ha seed rate achieved optimal wheat density
Increased cost without increasing yield
Graph depicts wheat yield from the 2012 Binnu trial.
The problem that we have with using high seeding rates to compete with weeds is that we often see no response to wheat yield.
In this trial the 40 kg/ha seed rate achieved the optimal wheat density for a 2 t/ha wheat yield.
So we increased our cost without increasing yield. If we estimate wheat seed cost to be $400 /t then it costs $4 for every 10 kg/ha increase in seeding rate.

11. Wheat yield
Graph depicts wheat yield from the Mingenew 2012 trial.

12. Summary
Increasing the seeding rate is a simple, effective method to increase crop competition
Often requires an increase in cost & is an inconvenience at seeding time, often with no yield benefit
Limit to the extra competition that can be achieved
May be more cost effective to increase crop competition through row spacing & crop row orientation
Summary - Increasing the wheat seeding rate is a simple, effective method to increase crop competition with weeds with no negative effects on the crop. However, often this technique requires an increase in cost to the grower and is an inconvenience at seeding time, often with no yield benefit Also, there is a limit to the extra competition that can be achieved by increasing seeding rate of wide row (eg. 30cm / 12” or greater) crops. - High crop seeding rates are a good, reliable non-herbicide weed management tool, however, it may be more cost effective to increase crop competition through row spacing and crop row orientation.