Project AbstractCanola seed costs are substantial, but seedling emergence is quite low ranging from 40-60%. This project was conducted from 2008 to 2010 at four western Canada locations including Lacombe, Lethbridge in Alberta and Indian Head and Scott in Saskatoon to determine the influence of seeding speed (4 vs 7 mph) and seeding depth (1 vs. 4 cm) on the emergence, maturity, yield, and seed quality of glyphosate-resistant canola. While the seeding depth did not influence average canola yield, it often had a major impact on canola emergence density. Under moist conditions, average canola emergence improved from 37 to 62% as seeding depth decreased from 4 to 1 cm, respectively. Seeding at a depth of 1 vs. 4 cm also decreased days to emergence, increased canola ground cover, decreased days to flowering and days to maturity and tended to decrease green seed levels. Relatively high canola emergence rates can reduce the need for additional herbicide applications, herbicide input costs and selection pressure for herbicide resistance. Relatively high canola stand densities can improve the ability of canola to successfully tolerate and accommodate biotic and abiotic stress. |
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Project Objectives
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Methods |
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Direct-seeded (no-till) experiments were conducted in western Canada from 2008 to 2010 at Lacombe, Lethbridge in Alberta and Indian Head and Scott in Saskatoon. All plots were established on no-till fields previously sown to wheat (Triticum aestivum L.) or barley (Hordeum vulgare L). Prior to seeding, a single pre-seeding glyphosate application (450 to 900 g a.e. ha-1) was applied to the entire plot area to control emerged weeds. The effect of seeding speed (4 vs 7 mph) and seeding depth (1 vs. 4 cm) was studied on canola cultivar (hybrid vs open-pollinated) growth and yield. A combination of eight factorial treatments (2 x 2 x 2) was arranged in a randomized complete block design with four replications.
Plot size was 4 by 12-15 m at all locations. Treatment factors and levels were as follows: cultivar (hybrid vs. open-pollinated), seeding speed (4 vs 7 mph), and seeding depth (1 vs. 4 cm). The hybrid (71-45RR) and open-pollinated (34-65RR) cultivars were both glyphosate-resistant. Canola was seeded from late April to mid May using 1 cm-wide knife openers on 23- to 30-cm row spacings at 150 seeds m-2. Fertilizer (N, P2O5, K2O, and S) was side banded during planting 2 cm beside and 3-4 cm below the seed row at recommended levels based on soil tests. Glyphosate was applied at 450 g a.e. ha-1 at the two- to three-leaf stage of the canola and before the six-leaf stage if necessary for later-emerging weeds. The plots were essentially kept weed-free.
Measurements
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Results
Seeding Depth –
Seeding canola at a depth of 1 vs. 4 cm led to several positive agronomic outcomes (Table 1). Shallower seeding reduced the time of crop emergence from 18 to 16 d. Earlier crop emergence enhances crop competition with weeds. Canola emergence density and ground cover was also improved by seeding at 1 vs. 4 cm (Fig. 1). Based on a seeding rate of 150 seeds m-2, canola emergence density increased from 37 to 45% as seeding depth decreased from 4 to 1 cm. Higher seeding density has been shown to decrease weed biomass and weed biomass in previous studies such as Harker et al. 2003. In a summary of 91 crop-weed competition cases, only six ‘‘failed to show decreasing weediness with increasing crop density’’ (Mohler 2001). Therefore, seeding at a 1 vs. 4 cm depth may alleviate the need for additional herbicide applications and improve integrated weed management as well as herbicide resistance management.
Although canola has a relatively high ability to compensate for low stand density given adequate growing season precipitation, the compensation process delays plant maturity, which may expose canola to yield-limiting high temperatures during the reproductive period and increases the possibility of higher green seed levels. In this study, seed yield was not significantly influenced by seeding depth (P = 0.227). However, green seed levels had a tendency (P = 0.086) to increase when seeding depth was increased to 4 cm (Table 1), and therefore, reduce canola grade from No. 1 to No. 2. A 1-d delay in crop maturity for the 4-cm seeding depth may help explain the tendency for higher green seed levels. A 2-d increase in flowering duration after seeding at a depth of 1 vs. 4 cm could be the result of less flowering stress due to earlier emergence and lower temperatures during flowering or to greater soil moisture availability given earlier and greater canopy cover.
Table 1: The effect of seeding depth (1 vs 4 cm) on canola performance
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Depth 1 cm |
Depth 4 cm |
p-value |
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Days to emergence |
16 |
18 |
<0.001 |
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Emergence density (plants m-2) |
67 |
56 |
0.002 |
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Ground cover (%) |
43 |
36 |
0.002 |
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Days to flowering |
54 |
55 |
<0.001 |
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Flowering durations (days) |
19 |
17 |
0.017 |
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Days to maturity |
112 |
113 |
<0.001 |
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Seed protein (%) |
23.7 |
23.9 |
0.023 |
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Green seed (%) |
2 |
2.3 |
0.086 |
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| Figure 1: Hybrid canola seeded at the depths of 1 (left) and 4 (right) cm at 4 mph at Lacombe research center. Source: Harker et al. Can. J. Plant Sci. (2012) 92: 795-802 doi:10.4141/CJPS2011-189 |
Seeding Speed
Increasing seeding speed from 4 to 7 mph tended to reduce canola emergence density (P = 0.054) from 41 to 38 plants. Seeding speed also had a tendency to interact with seeding depth to influence canola ground cover (P = 0.057). Seeding shallow at the lowest speed led to higher percent ground cover (46%) than any other seeding depth by seeding speed combination (Table 2). The latter combinations all led to similar canola ground cover levels. Therefore, combining the lowest seeding speed with the shallowest seeding depth could improve the ability of canola to compete with weeds and may alleviate the need to augment initial herbicide applications with a follow-up treatment.
Table 2: The interaction effect of seeding speed and seeding depth on canola ground cover
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Seeding Speed |
Depth 1 cm |
Depth 4 cm |
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(mph) |
% |
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4 |
46 |
36 |
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7 |
40 |
37 |
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LSD (0.05) |
6 |
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Recommendations
Canola growers can improve canola emergence density by seeding canola at a depth of 1 cm. Seeding speed influenced canola variables to a much smaller degree than cultivar or seeding depth. Canola compensates for sparse or weak canopies, but this can lead to a delay in crop maturity, increasing the potential for heat stress and green seed grade losses. Improved canola emergence density facilitates competitive crop canopies that require fewer herbicide applications and, therefore, reduce selection pressure for weed resistance to herbicides.
In this study, canola emergence was positively associated with precipitation. On the Canadian prairies and across the Great Plains, the soil moisture conditions necessary for optimal crop emergence are most likely to be found in direct-seeding systems. Precipitation levels cannot be managed, but soil water availability and precipitation retention is greater in direct-seeding systems.
Taking a ‘‘recipe’’ approach to a 1-cm seeding depth is not appropriate for all conditions. Extremely dry surface soil conditions may necessitate planting at deeper levels to ensure adequate seed germination. However, in most Canadian prairie canola production areas, seeding at a depth of 1 cm will not only improve canola emergence density, but will also decrease days to emergence, increase canola ground cover, decrease days to flowering and days to maturity and tend to decrease green seed levels.
Publication
Harker et al. Can. J. Plant Sci. (2012) 92: 795-802 doi: 10.4141/CJPS2011-189 https://cdnsciencepub.com/doi/pdf/10.4141/cjps2011-189