Compete with weeds give your crop heaven and your weeds hell

Transcription

1 Compete with weeds give your crop heaven and your weeds hell Peter Newman & Christine Zaicou-Kunesch, Department of Agriculture and Food KEY MESSAGES Weeds are a problem in crops because they compete for resources. The crop needs to compete back or the weeds will. There is a very short list of non-herbicide weed control tools available. Crop competition is one of them. AIMS To demonstrate the benefits of improved crop competition on weed growth and crop yield. METHOD Two trials were established in 212 to evaluate the interaction between paired row sowing, wheat seeding rate and herbicide. Paired row sowing was achieved by mounting Stiletto seeding boots to the DAFWA cone seeder. The Stiletto seeding boot is a machinery adaptation that is mounted onto a single tyne that creates paired crop rows 75mm apart. This way the modified seeding machine effectively reduces row spacing by 75mm and the length of crop row is doubled compared to single row sowing. For this research we attempted to compare paired row sowing with single row sowing. For the single row sowing treatments we mounted a single seed tube to the rear of the Stiletto boot to ensure that each plot had identical levels of cultivation. However, the soil disturbance created by the Stiletto boot resulted in the single row treatments being scattered (fuzzy rows) across a 75mm band. Mingenew (MIG) The Mingenew trial site was located 15km NE of Mingenew on red loamy soil. A site with high ryegrass density was chosen (179 ryegrass plants/m 2 in crop) To improve seeding operations, the site was burnt by the grower to reduce the high wheat stubble loads. The site was sown with Mace wheat on 8 May 212 after approximately 1mm rain fell over the previous three days. Another 6mm of rain fell on 9 May. Sakura 118g/ha was applied to the plus Sakura plots immediately before seeding in 8 L water/ha; AIXR2 nozzles, 12km/h. Fertiliser at sowing was Urea 5 kg/ha top dressed in front of seeder, Agstar 1 kg/ha was drilled via fertiliser tube on Stiletto boot (ie. between seed rows). Wheat and ryegrass density counts conducted on 18 June. The whole site was sprayed with Velocity for broadleaf weeds. On 12 September one biomass cut per plot of a.5m 2 quadrat was taken. The samples were taken to the lab and separated into wheat and ryegrass. Ryegrass and wheat tillers were counted, dried and weighed separately. On 22 October eight ryegrass seed heads per plot were measured for seed head length. Fifty ryegrass seed heads were individually sampled and the number of seeds per head were counted. An estimate of ryegrass seed production per mm of seed head length was made. Ryegrass seed set was estimated by multiplying ryegrass tiller number x seed head length x ryegrass seeds per mm of seed head. The trial was harvested by plot harvester on 25 October and grain samples processed for screenings, hectolitre weight and protein. Binnu The Binnu trial site was located 15km NE of Binnu on yellow sandy soil. A site with high wild radish density was chosen (approximately 3 wild radish/m 2 in crop). The site was sown with Mace wheat on 7 May 212 after approximately 1mm rain fell over the previous three days. Another 2mm of rain fell on 9 May. Fertiliser at sowing was Urea 5 kg/ha top dressed in front of seeder and Agstar 1 kg/ha was drilled via fertiliser tube on Stiletto boot (ie. between seed rows). The whole site had also been spread with SuperCuZnMo 2 kg/ha and lime sand 1.5 t/ha. Wheat density counts conducted on 21 June. The whole site sprayed with Velocity for broadleaf weeds, however a 1m strip of weeds was missed with the sprayer. On 13 September one biomass cut per plot of a.5m 2 quadrat was taken from the area of un-sprayed crop. Wild radish and wheat were counted, dried and weighed separately. The trial was harvested by plot harvester on 29 October and grain samples processed for screenings, hectolitre weight and protein. RESULTS 213 WA Crop Updates

2 Mingenew ryegrass There was no difference in wheat density, wheat biomass, ryegrass density, ryegrass tillers, wheat tillers, wheat quality or yield between single (fuzzy) row and paired row sowing (p>.5). Ryegrass seed set was significantly reduced by increasing seeding rate (p<.5; lsd 2768 seeds /m 2 ) (Figure 1). The following results are an average of single and paired row sowing systems. 2 MIG stiletto - ryegrass seeds /m 2 Ryegrass seeds /m kg/ha (138 8kg/ha (179 12kg/ha (255 16kg/ha (297 Plus Sakura Minus Sakura Figure 1: Ryegrass seed production per m 2 at Mingenew for four seeding rates, plus and minus Sakura herbicide 118 g/ha pre-sowing (average of single and paired row sowing). Wheat plant density is shown in brackets. A closer look at the plus Sakura treatments, shows that although the ryegrass number was significantly reduced by the herbicide, seeding rate still had a big impact on ryegrass seed (Figure 2). Ryegrass set 811 seeds /m 2 for the 4 kg/ha seed rate treatment compared to 178 seeds /m 2 for the 12 kg/ha seed rate. This represents a 78% reduction in ryegrass seed set. Ryegrass seeds /m MIG Stiletto - ryegrass seed set per m 2 -Plus Sakura 4kg/ha (138 8kg/ha (179 12kg/ha (255 16kg/ha (297 Figure 2: Ryegrass seed production per m 2 at Mingenew for four seeding rates for plus Sakura herbicide 118 g/ha pre-sowing treatments only. Wheat plant density shown in brackets. 213 WA Crop Updates 2

3 Dry weight (g/m 2 ) Wheat yield (kg/ha) There were significant differences in yield between seed rates with the highest seeding rate significantly yielding more than the lowest seeding rate (p<.5; lsd 179 kg/ha). There was no difference in yield between plus and minus Sakura (p>.5). There was no positive interaction between herbicide and seed rate (p>.5) (Figure 3). MIG Stiletto - Wheat yield Minus Sakura Plus Sakura 4kg/ha (138 8kg/ha (179 12kg/ha (255 16kg/ha (297 Figure 3: Wheat yield (kg/ha) at Mingenew for four seeding rates, plus and minus Sakura herbicide 118 g/ha presowing treatments only. Wheat plant density shown in brackets. Binnu wild radish Binnu - wheat and wild radish dry weight - 13 Sept wheat wild radish 5 4kg/ha (12 8kg/ha (163 12kg/ha (222 plants /m2) 16kg/ha (287 Seed rate / wheat density 213 WA Crop Updates 3

4 Figure 4: Wheat and wild radish (un-sprayed) dry weight (g/m 2 ) at Binnu as measured on 13 September from area of trial where no post-emergent herbicide was applied. There were significant differences in wild radish dry weight between seeding rates (p<.5; lsd 115 g/m 2 ) (Figure 4). With the exception of protein at the Binnu site, there was no effect of seeding rate on grain quality at both sites. Grain protein increased as seeding rates increased at Binnu (Table 1). There was no difference in wheat yield between seeding rates at Binnu (p>.5) (Table 1). Table 1: Wheat yield (Binnu trial) and grain quality for Binnu and Mingenew trials. Seeding rate 4kg/ha 8kg/ha 12kg/ha 16kg/ha Binnu Wheat yield (kg/ha) n.s. Wheat density (plants /m 2 ) Protein (%) Screenings (%) n.s. Hectolitre Weight (kg/hl) n.s. Mingenew Wheat density (plants /m 2 ) Protein (%) n.s. Screenings (%) n.s. Hectolitre Weight (kg/hl) n.s. lsd CONCLUSION This research demonstrates what many other crop competition trials have demonstrated in the past. As crop density increases, crop biomass increases and weed growth and seed set decreases (Figures 1,2 & 4). The concept is not new. The challenge is to do this in a practical and cost effective way. The trend in Western Australia in recent years has been increasing row spacing, reducing seeding rates and the sowing of un-competitive cultivars. There are good, solid reasons for this trend, but the question is how much is it costing us in crop yield and weed control? Paired row sowing achieved using the Stiletto boot in this trial, has the potential to improve grain yield and competition with weeds. Unfortunately this research failed to demonstrate the difference between paired row and single row sowing due to the single row treatments being sown as a fuzzy row. However, what we did see from paired row sowing was the ability to achieve high crop densities with an effective reduction in crop row spacing. Benefits of paired row sowing Row spacing Paired row sowing effectively reduces the crop row spacing without adding extra tynes to the seeding machine. The stiletto boots used in this research creates paired rows, 75mm apart, effectively reducing the row spacing by 75mm. For crops with a yield potential of 2 t/ha or more, there is a reliable, linear grain yield response to narrow row spacing. Past research has also reliably demonstrated a linear response between row spacing and weed growth. Doubles length of crop row Paired row sowing effectively doubles the length of crop row in a paddock compared to single row sowing at the same row spacing. This means that there is less in-row competition between crop plants, enabling a higher number of seeds to germinate and establish as seeding rates increase. 213 WA Crop Updates 4

5 Maintain tyne spacing Existing seeding machinery can be modified for paired row sowing. Thus the tyne spacing that enables stubble handling / acceptable sowing speed can remain the same. Mingenew trial The Mingenew site clearly demonstrated the benefits of increased crop density. For the nil Sakura treatment there was a large reduction in ryegrass seed set (Figure 1). In the absence of pre-sowing grass selective herbicide, ryegrass set 17 seeds /m 2 for the 4 kg/ha seed rate compared to 6 seeds /m 2 for the 16 kg/ha seed rate. This represents a 65% reduction in ryegrass seed set. What was even more encouraging was the combination of herbicide and crop competition. In the presence of Sakura pre-sowing, ryegrass set 811 seeds/m 2 for the 4 kg/ha seed rate compared to just 178 seeds/m 2 for the 12 kg/ha seed rate (Figure 2). This is a 78% reduction in ryegrass seed set as a result of crop competition. The other way to look at this is that increasing crop density took Sakura from a 95% herbicide to a 99% herbicide in terms of seed set. Wheat yield increased with seeding rate at the Mingenew site. In the presence of Sakura pre-sowing, maximum wheat yield was achieved at 8 kg/ha. However, in the absence of Sakura pre-sowing, maximum wheat yield was achieved at 12 kg/ha seed rate. This is likely due to the extra competition from ryegrass suppressing wheat yield for the nil Sakura treatments. Using the crop density rule of thumb of 5 wheat plants per tonne of grain yield potential, it should have been possible to achieve maximum yield at the lowest seeding rate. However, this rule of thumb applies to weed free crops. As with many trials in the past, there was no negative effect of increasing seeding rate on grain quality despite the vocally pronounced anecdotal evidence that high seeding rates result in high screenings levels. Binnu trial The Binnu trial demonstrated that improved crop competition can also have an effect on wild radish. The wild radish measured to demonstrate this point received no in-crop herbicide. Increased wheat density resulted in significant reduction in wild radish biomass (Figure 4). Future research should focus on what impact this may have on the ability to control wild radish with post-emergent herbicide. There was no effect of seeding rate on wheat yield, keeping in mind that only a narrow, one metre wide strip of wild radish was left un-sprayed. Given the yield of 2 t/ha, the low seeding rate was adequate to achieve maximum yield. Cost effectiveness The big question is, if maximum yield can be achieved at relatively low seeding rates, is it cost effective to increase seeding rate to suppress weeds. This should be the subject of further investigation. The bottom line is that there are very few non-herbicide weed control tools available, crop competition with weeds is one of them. There may be no need to go to extremes of seeding rate, row spacing and cultivar, but there is no doubt that there is significant room for improvement. KEY WORDS Annual ryegrass, competition, seeding rate, paired row sowing, Sakura. ACKNOWLEDGMENTS Many thanks to Steve Cosh, Larry Prosser, Dave Nicholson and Trevor Bell from the Geraldton RSU team who conducted the trials and made this work possible through the seeder modifications. Thank you also to GRDC for their support of this research. Project No.: Paper reviewed by: DAW196; DAW218 Brenda Shackley 213 WA Crop Updates 5