Row orientation and weed competition


Research organisatons
Funding source

Trial details

Researcher(s) Amanda Cook, Nigel Wilhelm and Chris Dyson (SARDI)
Year(s) 2016
Contributor SARDI Minnipa Agricultural Centre
Trial location(s) Site 21, Minnipa Agricultural Centre, SA
Row orientation and weed competition locations

Controlling barley grass in upper EP farming systems is becoming a major issue for growers, due to the development of herbicide resistance and delayed weed emergence. Management options other than herbicides need to be considered to address the issue for long-term sustainability. One of the best bets for cultural control of barley grass in-crop may be increased crop competition. The Australian Herbicide Resistance Initiative (ARHI) based at University of Western Australia has shown an increase in grain yield with wheat and barley sown in an east–west (E-W) orientation over crops sown in a north-south (N-S) orientation due to a decrease in ryegrass competition. This effect is due to lower light interception by the weed due to the crop row orientation resulting in a decrease in weed seed (Borger, 2015).


A trial was established at Minnipa Agricultural Centre to investigate the impact of row direction and row spacing on weed competition and cereal performance over twoyears. The previous season’s research is reported in Eyre Peninsula Farming Systems Summary 2015, Row orientation and weed competition, p163.

Key messages
  • There was no detectable direct effect of sowing direction this season at Minnipa with a mild spring.
  • Using a narrow row spacing of 18 cm instead of 30 cm resulted in wheat yield increasing from 3 t/ha to 3.6 t/ha (19% increase).
  • Light interception was very sensitive to sowing direction, and not having ‘weeds’ resulted in higher light within the canopy in the north-south direction compared to east-west.
  • Knife point and ribbon seeding systems achieved similar crop establishment and crop performance.
Lead research organisation Central West Farming Systems
Host research organisation SARDI Minnipa Agricultural Centre
Trial funding source GRDC CWF0020
Related program Overdependence on agrochemicals

Thank you to Sue Budarick, Tegan Watts, Lauren Cook and Katrina Brands for sampling, processing the weed counts and managing the weed germination trays. Funded by the GRDC Overdependence on Agrochemicals project (CWF00020).

Other trial partners Upper North Farming Systems, BCG
Download the trial report to view additional trial information


Crop type Wheat
Treatment type(s)
  • Sowing: Method
  • Sowing: Row spacing
Trial type Experimental
Trial design Replicated

Minnipa Agricultural Centre 2016

Sow rate or Target density Weeds (oats as surrogate) 70 plants/m2
Sowing machinery

In 2016 a replicated plot trial was sown in blocks with two row orientations; E-W and N-S into a pasture paddock. The ten treatments within the row orientation blocks included two row spacings, 18 cm (7”) and 30 cm (12”), sown with two different seeding boots; a Harrington knife point and an Atom-Jet spread row ribbon seeding boot, both with and without ‘oat weeds’. An ‘oat’ weed only treatment was also sown at both row spacings with the Harrington knife points. Plots were direct drilled with press wheels. Oats were spread at 70 plants/m2 as a surrogate weed through the seeder on the ‘weed’ plots before the seeder pass.

Sow date 17 May 2016
Harvest date 4 November 2016
Plot size 20m x 2m
Plot replication 4
Paddock history 2016: Mace wheat 2015: Medic pasture 2014: Wyalkatchem wheat

18:20:0:0 (DAP) fertiliser at 60 kg/ha


The trial was sprayed on 16 May with a knockdown of 1.5 L/ha of glyphosate, and Broadside (MCPA; bromoxynil; dicamba) at 800 ml/ha on 22 June.

Download the trial report to view additional method/treatment information

Download results

Trial results Table 1

# Treatment 1
Crop Establishment (plants/m2) Protein (%) Yield (t/ha) Late dry matter (t/ha) Screenings (%)
1 sowing direction E-W 116 10.2 3.36 6.33 0.9
2 sowing direction N-S 108 10.3 3.3 6.4 0.9
3 row spacing 18cm 120 10.3 3.64 7.05 1
4 row spacing 30cm 105 10.3 3.02 5.68 0.9
5 knife points 114 10.3 4.03 6.13 0.9
6 knife points plus weed 115 2.58 6.61
7 ribbon 111 10.3 4.16 1
8 ribbon plus weed 110 2.52

Crop Establishment plants/m2


Late dry matter t/ha


Protein %


Screenings %


Yield t/ha

Observed trial site soil information
Trial site soil testing
Not specified
Soil conditions
Trial site Soil texture
Site 21, Minnipa Agricultural Centre, SA Red loam
Derived trial site soil information
Australian Soil Classification Source
Trial site Soil order
Site 21, Minnipa Agricultural Centre, SA Rudosol
National soil grid Source
NOTE: National Soil Grid data is aggregated information for background information on the wider area
Actual soil values can vary significantly in a small area and the trial soil tests are the most relevant data where available

Soil properties



Site 21, Minnipa Agricultural Centre SA 2016

Observed climate information

Rainfall avg ann (mm) 325mm
Rainfall avg gsr (mm) 241mm
Rainfall trial total (mm) 391mm
Rainfall trial gsr (mm) 268mm

Derived climate information

Site 21, Minnipa Agricultural Centre SA


Some data on this site is sourced from the Bureau of Meteorology

SILO weather estimates sourced from
Jeffrey, S.J., Carter, J.O., Moodie, K.B. and Beswick, A.R. (2001). Using spatial interpolation to construct a comprehensive archive of Australian climate data , Environmental Modelling and Software, Vol 16/4, pp 309-330. DOI: 10.1016/S1364-8152(01)00008-1.

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Trial last modified: 04-06-2018 15:04pm AEST