Take home messages
- Barley was more competitive with weeds than wheat, reducing both weed biomass and seed set by 0.5t/ha.
- Sowing direction did not influence crop yield or weed biomass and seed production.
- Wheat was more profitable than barley in the absence of weeds, but they were equally profitable in the presence of weeds.
Background
The reliance of farming systems on agrochemicals, particularly herbicides, has increased over time. As a result, the number of weed populations with some level of resistance to herbicides are increasing.
This is motivating growers to seek alternatives to herbicides for weed management. Questions have been raised about whether sowing direction can influence not only crop yields, but also weed pressure within crops. Work undertaken in Western Australia, and in previous experiments by BCG, have shown that crop sowing direction can impact weed biomass and seed set, however this is largely unproven in the West Wimmera region, particularly in relation to whether there are yield gains from one direction over another.
BCG sowing direction trials at Horsham have produced variable and inconsistent results and as a result, the Kaniva Landcare Group expressed interest in investigating the influence of sowing direction on crop yield and weed production in their local environment.
The benefit of carrying out this work is the ability to add to the previous research undertaken. Collating results over multiple sites and seasons leads to more confidence in ascertaining if there are situations where a ‘free’ management decision can alter crop yield and weed management.
Aim
To determine if sowing direction can influence grass weed populations, growth and seed set in wheat and barley, and whether there are direct benefits to grain yield from this practice.
Paddock details
| Location: | Kaniva |
| Annual rainfall: | 650mm |
| GSR (Apr-Oct): | 494mm |
| Soil type: | Grey vertosol |
| Paddock history: | 2015 canola |
Trial details
| Crop types: | Mace wheat and Compass barley |
| Treatments: | Two sowing directions – east-west and north-south, with and without weeds using tame oats (broadcast at 30 seeds/m²) as a surrogate weed |
| Target crop density: | 150 plants/m² |
| Seeding equipment: | Knife points, press wheels, 30cm row spacing |
| Sowing date: | 13 May |
| Replicates: | Four |
| Harvest date: | 22 November |
| Trial average yield: | Wheat 4.9t/ha, barley 5.9t/ha |
Trial inputs
| Fertiliser: | Granulock Supreme Z + Impact @ 50kg/ha at sowing Urea @ 90kg/ha at GS30 |
| Herbicides: | Diuron® @ 0.5kg/ha + Dual Gold® @ 0.5L/ha applied at sowing PSPE |
Broadleaf weeds, insects and disease managed to best management practice, where practical, in-line with farmer paddock management.
Method
A replicated trial was sown as a split plot design with sowing direction as the main plot and crop type by weeds as the sub-plot. Weed pressure was achieved by spreading tame oats and achieved a density of 30 plants/m² in half of the plots.
The trial was located within a grower’s paddock of wheat to allow easier management throughout the season with respect to nitrogen (N), herbicide and fungicide programs. This paddock had been canola the previous season and was thought to be low in ryegrass pressure, however early in the season it was noticed the ryegrass pressure was quite high in one replicate and as such hand weeding was conducted in weed free plots.
Assessments carried out in-crop included emergence counts of crop and weeds 40 days after sowing and biomass at GS65 (flowering). Plots were harvested and processed for standard yield and grain quality assessments, with oats being separated from a sub-sample to allow calculation of crop and weed yield within the weedy plots.
Results and interpretation
The 2016 season at Kaniva was very wet, with 473mm of rain recorded during the growing season. The trial was located on high ground that protected it from severe waterlogging, however there was one area in the trial that did hold some water in the spring which created some variability within the trial.
Given the wet spring and an inaccessible paddock, managing stripe rust in the wheat late in the season was a challenge. Assessment of stripe rust presence showed uniform distribution throughout the trial and although it could have impacted on wheat yields, it would not have interacted with treatments within species types.
Establishment and in-season growth
Both crops established at target densities, with sowing direction and presence of weeds not influencing the number of crop plants established. Weed establishment was also assessed and not found to be different in response to sowing direction (P=0.334) or crop type (P=0.537).
There was an interaction between crop type and sowing direction, with barley sown east-west producing more biomass at GS65 than wheat when sown east-west. There was no difference between crop types when sown north-south (Table 1).
Table 1. GS65 biomass (t/ha) for wheat and barley under different sowing directions.
The presence of weeds had a significant impact on crop biomass in both wheat and barley, however the overall effect was more pronounced in wheat (Table 2). This was reflected in weed biomass results, where barley suppressed weed growth to a greater extent than wheat. Sowing direction did not influence weed biomass production (P=0.501).
Table 2. GS65 biomass (t/ha) for wheat, barley and weeds.
Yield and quality
There was a near significant effect of sowing direction on grain yield (P=0.105), but the effect size was small with east-west yielding 0.24t/ha more than north-south.
Barley (6.34t/ha) yielded more than wheat (5.5t/ha, P=0.001) and weeds reduced yield by 1.2t/ha in both wheat and barley (P<0.001). There was no interaction between the presence of weeds and crop type.
Weed seed set
The final aspect assessed in this trial was whether sowing direction or crop type could influence seed set in the model weed (tame oats).
It was found sowing direction had no influence on weed seed set (P=0.257). Crop type did have a significant influence on oat seed yield with more oat seed being set in the wheat, 1.3t/ha as compared to barley, 0.8t/ha (P=0.005, LSD=0.17, CV%=35.2). This was as expected with barley being a more competitive crop than wheat with greater early vigour and shorter time to stem elongation. However, this is influenced by variety selection and nutrition, sowing rate, row spacing and so on.
Commercial practice
In all experiments conducted by BCG, sowing direction has only had a small or non-significant effect on grain yield. It is therefore unlikely to be a silver bullet for improved crop yields.
In terms of weed management, this trial found no direct influence of sowing direction on weed establishment, growth or seed set. The establishment and biomass production results in this trial correlate well with work undertaken at Jil Jil in 2015 (page 117) and 2016 (page 176), indicating that sowing direction has minimal impact on weed establishment and growth as a result of the crop taking time to develop to a point where there is competition for resources.
Seed set seems to depend a little on weed species present and season. In 2015 at Jil Jil (using tame oats) it was found that there was no difference in panicle number or seed set, whereas in the presence of brome in 2016, there was a near-significant result with east-west sowing having reduced seed production. This was deemed a plausible result due to the difference in light interception by the crop, with east-west sowing restricting light to the weeds underneath more.
This experiment has confirmed the superior competitive nature of Compass barley compared to Mace wheat, and that crop selection is an important tool to reduce weed biomass and ultimately seed set. However, the difference between the two may have been overestimated in this trial due to the effect that stripe rust had on the wheat in spring.
On-farm profitability
If sowing direction was to change yield, or crop competitive ability, it would be a low cost change to the farming practice, however it was found in this experiment that there is no effect of sowing direction on either of these parameters.
Crop choice, however, could be a different story. Barley is inherently lower value than wheat, but generally offers higher yields so there is a trade-off between yield and price received. This is shown in Table 3 where returns based on the quality achieved are used to calculate gross margins. It shows that even with higher barley yields, wheat achieved a better gross margin in a weed free situation, but there was little difference in return in the presence of weeds due to the superior competitive ability of barley.
Table 3. Gross margin $/ha for crop type and weed presence in 2016.
References
Acknowledgements
This research was funded by the Kaniva Landcare Group as part of the National Landcare Program – Sustainable Agriculture Small Grants Round 2015-16. Project Code SGRI-0550/Kaniva District Landcare.
