Three to four weeks after planting winter canola is a good time to go back and determine how well the seeding pass went and if the target plant density was achieved. This can be done by counting the final number of plants that were effectively established (Figure 1).
Figure 1. Final number of canola plants established after emergence. Photo by Ignacio Ciampitti, K-State Research and Extension.
Two approaches to doing this will be discussed in this article. The target plant density for open pollinated varieties is approximately 400,000 to 500,000 plants per acre, and for hybrids it is 200,000 to 350,000 plants per acre.
As winter canola varieties and seeding technology improve, different approaches to calculating seeding rate may be used to achieve a “target plant density.” For example, southern Great Plains producers often base seeding rate on pounds per acre. This approach works okay, but number of seeds per acre can vary widely between open pollinated varieties and hybrids because of differences in seed size. A more accurate approach is used by Canadian farmers. Both seed size (grams per 1,000 seeds) and the seed weight per unit of area (lbs/acre) are used for deciding the final number of plants per acre or target plant density. An example of this approach is illustrated in Table 1.
Table 1. Canola target plant density as related to the total seed weight (lbs/acre) and seed size (grams per 1000 seeds).
|
Seed size (grams per 1000 seeds) |
Seeding Rate (lbs/acre) |
||||
|
2.00 |
3.00 |
4.00 |
5.00 |
6.00 |
|
|
|
Plant Density (plants/acre) |
||||
|
3.5 |
259,198 |
388,797 |
518,397 |
647,996 |
777,595 |
|
4.5 |
201,599 |
302,398 |
403,197 |
503,997 |
604,796 |
|
5.5 |
164,944 |
247,417 |
318,314 |
412,361 |
494,833 |
|
6.5 |
139,568 |
209,352 |
279,137 |
348,921 |
418,705 |
Usually farmers plant more seeds than what effectively becomes the final plant density. We typically expect 65 to 85 percent of seeds to produce a viable plant. Thus, seeding rates must take into consideration the following factors: seed quality (germination), soil type (sandy vs. fine texture), crop management practices (e.g. tillage systems, planting depth), environment (wet fall, cold temperatures), pest problems, and all their interactions. For example, heavy rains after planting combined with soils susceptible to crusting will more likely reduce the final number of plants established. Successful establishment is a key factor for attaining high canola yields.
Because of the differences between seeding rates and optimum densities for open pollinated varieties and hybrids, K-State is conducting a seeding rate by cultivar study at Manhattan and the South Central Experiment Field near Hutchinson in 2013-2014. We are examining low, optimum, and high seeding rates for both types of cultivars. We hope to develop more accurate seeding rate recommendations based on plants per acre and seed size for Kansas canola producers.
Why is it important to have uniform stands?
Plant-to-plant uniformity at emergence is critical for improving weed control and uniform plant maturity. However, winter canola will compensate for a poor plant stand if a uniform stand is not obtained.
How does canola compensate for stand reductions?
Canola compensates for missing plants by taking advantage of the soil and water resources available, which promotes branching. High fertility levels also encourage branching. Yields reductions of 30 to 40 percent occur when 1 or 2 plants per square foot are present compared with the optimum plant density. A good rule of thumb is if 20 percent or less of the target plant density is achieved, then we often see larger reductions in yield.
Planting hybrid canola is one way to help alleviate a poor stand as hybrids tend to have increased seedling vigor and more vigorous branching.
How can I measure effective canola stand?
There are several approaches, but we will focus on two methods.
1. “Known Area Method”
One of the most common approaches is to use a “hoop” or other shape of a known size. The idea is to toss the hoop in different sections of the field to make the counts as random as possible. This allows for proper representation of the natural variation in the field. Avoid subjective measurements on dense areas; this will produce biased results if the particular zone is not fairly representative of the entire field. Within the known area, count the total number of plants. If the hoop has a 24-inch diameter, that represents 1/15,000th of an acre. If you count 20 plants inside the hoop, the plant density would be about 300,000 plants per acre. The number of plants within the hoop will depend on the row spacing, seeding rate, and the factors that affect establishment mentioned above. For canola hybrids seeded at 8-inch row spacing at low plant density (100,000 seeds/acre), the number of plants within a 24-inch hoop should be around 7 plants. If the desired plant density is on the upper end (500,000 seeds/acre), the total number of plants should be around 35 plants within a 24-inch hoop.
Take counts in 10 to 20 spots in the field to get an average for the effective canola stand. Farmers may use a rectangle or a square for measuring the total number of plants within the field. The keys are to associate the size of the known area with an acre in units and to get a representative sample.
2. “Plants-in-a-Row Method”
Another approach for measuring the final stand density is by counting the total number of plants per unit of row length (Figure 2). Again, this procedure needs to be repeated in different areas to account for the natural field variation.
Figure 2. Determining final stand density for canola by counting the total number of plants in a row length. Photo by Ignacio Ciampitti, K-State Research and Extension.
If the target number of plants per unit of acre is approximately 500,000 (assuming 8-inch row spacing), then for one-foot of row length the final number of plants should be close to six. The following table provides target plant densities related to row spacing and plants per foot of row-length for winter canola.
Table 2. Target plant density (plants/acre) as related to the row width and the number of plants per unit of foot row-length.
|
Plants per foot of row-length |
Row width |
||
|
8-inch |
10-inch |
12-inch |
|
|
|
Plant density (plants/acre) |
||
|
2 |
261,360 |
209,088 |
174,240 |
|
4 |
392,040 |
313,632 |
261,360 |
|
6 |
522,720 |
418,176 |
348,480 |
|
8 |
653,400 |
522,720 |
435,600 |
|
10 |
784,080 |
627,264 |
522,720 |
|
12 |
914,760 |
731,808 |
609,840 |
Crop growth until winter
At this time of the growing season, canola is in the rosette stage (Figure 3). The plant height remains unchanged as the stem increases in thickness and the root system is established. In the southern Great Plains, canola overwinters in this stage. A larger canola canopy will produce more carbohydrate reserves, out-compete weeds, improve canopy closure, increase water use efficiency by diminishing losses to evaporation, and increase total dry mass production of above- and below-ground structures including root growth and exploration.
Figure 3. Canola crop at the rosette stage. Photo by Ignacio Ciampitti, K-State Research and Extension.
Figure 4. Larger older leaves of canola at the bottom of the plant and smaller young new leaves at the center of the rosette. Photo by Ignacio Ciampitti, K-State Research and Extension.
During the winter, some or most of the leaf tissue will be lost, but as long as the crown (center of rosette) does not turn brown or die, the plant will resume its growth as soon as the temperature increases during the early spring.
Summary
For more information, covering canola production and best management practices, see the newly revised Extension publication MF-2734 “Great Plains Canola Production Handbook” http://www.ksre.ksu.edu/bookstore/pubs/mf2734.pdf
Ignacio Ciampitti, Cropping Systems and Crop Production Specialist
ciampitti@ksu.edu
Mike Stamm, Canola Breeder
mjstamm@ksu.edu
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