Chapter 8 - Crop Establishment

Crop Establishment

Uniform, vigorous crop establishment is one of the keys to achieving high yielding canola crops. This chapter describes crop establishment factors such as pedigreed seed, seeding date, rate and depth of seeding, and row spacing.

The previous chapter emphasized the critical requirement for an ideal seedbed for canola. Altering practices such as seeding date have relatively little effect on input costs but can have a large impact on yields and, therefore, the profit from the crop. Successful stand establishment results from rapid, uniform seedling emergence, which depends partly on high quality, genetically pure seed. In Canada, the genetic purity of canola seed is controlled by the pedigree system, whereas the physical and biological quality of seed is maintained through standards in the Canada Seeds Act.

Pedigreed Seed

The genetic characteristics of a seed influence its response to environmental conditions. Plant breeders develop varieties with the desired genetic traits for optimum yield in certain environments and to meet quality specifications demanded by the marketplace. The small amount of seed for each new variety produced by plant breeders must be multiplied rapidly with a minimum of genetic change or contamination before release to commercial canola growers. In Canada, this is achieved with a pedigreed seed production system.

The Canadian Seed Growers' Association (CSGA) is designated by the Canada Seeds Act to be the sole pedigreeing agency for most crops in Canada. The CSGA establishes genetic standards and ensures that these standards are maintained. The CSGA's responsibility covers varieties developed by the public and private sectors.

There are two stages in the production and identification of pedigreed seed. First is the production and inspection of the seed crop. Approved crop inspectors inspect pedigreed seed crops and report to the CSGA on the conditions of these seed fields. The inspectors verify the variety sown, previous land use, isolation, weed infestation, plants of other crop kinds, and the degree of contamination with other varieties or off-types. Crops that meet the standards are issued a crop certificate by the CSGA.

The second stage is the inspection of the seed by a licensed grader at an Authorized Establishment or by an inspector to determine the grade under the Canada Seeds Act. Factors assessed include germination, freedom from weed seeds, sclerotia bodies, other Brassica crop kinds and overall quality.

Pedigreed canola is multiplied through the following seed classes:

• breeder
• select (synthetic)
• foundation
• certified

Seed Classes

Breeder seed refers to seed of a variety produced by the plant breeder or a breeder responsible for maintenance of that variety. Breeder seed is the source for all future multiplication of that variety. The breeder determines the number of generations of breeder seed produced. Breeder seed is supplied to certain pedigreed seed growers authorized by the CSGA to produce the next class of seed.

Select (synthetic) is a physical blend of either Breeder or Foundation seed used in the production of some certified canola varieties. Due to obligate cross pollination (or "outcrossing") in B. rapa, a mixture of parents will result in some hybridity. A breeder wishing to produce this type of seed must notify the CSGA with the details of the varieties being mixed, including the proportion of each. There are now a few synthetic B. napus varieties, but the level of hybridity will be lower than with B. rapa synthetics.

Foundation seed is the seed produced from crops grown with breeder or select seed by foundation seed growers who have served a three-year probation period in plot production. Unlike breeder seed, only one generation of foundation seed is allowed.

Certified seed can be grown from breeder, select or foundation seed and is the class recommended for commercial canola production. Only one generation of certified seed is allowed. Commercial canola growers in Canada use a higher percentage of certified seed compared to growers of other field crops. Seed produced from a crop grown from certified seed is no longer pedigreed and it is illegal to advertise or sell it under a variety name. Such seed is classed as "common seed."

This short multiplication chain for pedigreed canola seed maintains the genetic purity of each variety and its agronomic/quality characteristics. B. rapa canola must crosspollinate, while B. napas canola typically has 20 to 30% outcrossing. This ability for cross-pollination is why there are fewer pedigreed classes for canola than many other crops. With cross-pollinated crops, the more generations removed from the original breeder seed, the greater the likelihood that outcrossing will have occurred and, therefore, some of the seed may no longer carry the genetically superior qualities.

Certified seed provides an extremely close copy of the genetic characteristics of the original breeder seed, as well as strict standards for weeds (especially wild mustard and cleavers) and high germination. Non-pedigreed or common seed provides no assurance of either genetic purity or quality. Crops grown from non-certified seed may have outcrossed with volunteer or neighbouring plants that lack the desired quality or agronomic traits. Certified seed has a low tolerance for contamination by other varieties. The current tolerance is 1.5 plants for every 10,000 plants. Although this tolerance is very low, the number of off-types or other varieties in a field planted with certified seed could be noticeable. For example, given a 107.6 plants/m2 (10 plant/ft²) stand establishment, and a maximum contamination of 1.5/10,000 in the seedlot, this would create 160.6 off-types/ha (65 off-types/ac). The off-types could be herbicide-tolerant (HT) varieties in a conventional variety. This explains why some growers find HT volunteers after seeding a conventional variety from a certified seedlot on land that was not previously seeded to HT varieties or close to a field of HT canola.

Plant Breeders' Rights

Plant breeders incur substantial costs to develop valuable varieties and thus they wish to protect them from pirating. Canada's Plant Breeders' Rights Act, enacted in 1990, allows plant breeders to control the seed of new varieties that they develop and collect royalties on them for 18 years. Similar to a copyright or patent, Plant Breeders' Rights (PBR) protect the research investment made to develop new crop varieties. Proponents of PBR contend that plant breeding is the most cost-effective way to achieve increases in yields, quality and disease resistance.

PBR protection is an exclusive right to sell and produce the seed in Canada. Further sales for propagation purposes are not allowed without the approval of the breeder. Farmers are allowed to save some seed for their own replanting purposes, but sales to other individuals or corporations are prohibited. Seed companies are taking action to protect their investments. Twenty-one of these companies have formed the Canadian Plant Technology Agency (CPTA). The agency has a mandate to educate and help enforce the intellectual property rights of member companies.

The Canada Seeds Act

All canola seed sold in Canada must meet minimum standards for physical purity and germination as set under the federal government's Canada Seeds Act, which is administered by Agriculture and Agri-Food Canada.

Seed which has received CSGA pedigreed status must be analyzed by an accredited seed grader for weed seeds, other crop kinds and general quality before the seed can be sold. The accredited grader obtains a germination test of the sample from an accredited lab before grading the seedlot. If the seed meets all standards, it is bagged and sealed under the direction of an inspector or accredited grader with each bag tagged with the appropriate seed grade designation.

The Act sets the maximum tolerances (Table 1) for primary noxious weed seeds such as:

• wild mustard
• secondary noxious weed seeds such as stinkweed, Canada thistle and wild oats
• other weed seeds such as green foxtail
• seeds of other crops

Table 1. Seed Grade Standards for Canola (Table VII from Schedule I of Canada Seeds Act)

	Maximum Number of Seeds Per 25 g						Maximum Number of Sclerotes per 50 g	Minimum % Germination
	Primary Noxious	Primary + Secondary Noxious	Total Weeds	B. rapa in B. napus or Vice Versa	Other Brassica Crops Including S. alba	Non-Brassica Crops
Canada Foundation No. 1	0	0	5	0	0	1	1	90
Canada Foundation No. 2	0	0	10	2	1	2	2	75
Canada Registered No. 1	0	0	5	0	0	1	1	90
Canada Registered No. 2	0	0	10	2	1	2	2	75
Canada Certified No. 1	0	1	5	5	1	1	1	90
Certified No. 2	0	2	10	10	5	2	2	80
Common	1	3	15	20	15	2	2	90

Seed shall be free from seeds of cleavers (Galium aparine L. and G. spurium L.)

The benefits of certified seed from a weed control perspective alone are evident when the tolerances under the Act are reviewed. At a seeding rate of 5.6 kg/ha (5 lb/ac) using common seed containing the maximum allowable number of weed seeds, a farmer could plant 80 primary noxious, 240 secondary noxious and 2,965 total weed seeds per ha (1,200 total weed seeds per acre). The lower tolerance for weed seeds in the certified class would result in far fewer weed seeds being sown.

When considering a purchase of certified seed, ask the seed supplier for the weed seed analysis of the seedlot. Talk to your seed supplier well in advance so that the information is available before purchase. Access to the results of such an analysis done by an accredited seed laboratory is a right for all seed buyers as specified in the Canada Seeds Act. This information can help growers avoid the introduction of new weeds to their farms.

Seed Vigour

Growers and agri-retailers often associate seed quality with germination percentage. However, the standard germination test does not consistently predict the field performance of a seedlot. For example, in a three-year study on the prairies, Agriculture and Agri-Food Canada researchers planted different seedlots of certified Westar and Tobin canola, and found yield differences up to 14% between Westar seedlots and 22% between Tobin lots. Stand establishment was related to the germination percentage for Westar but not for Tobin. Neither germination nor stand establishment accurately predicted seed yield of either variety. Therefore, there are significant differences in seedlot yield potential that cannot be predicted by the standard germination test.

Another seed quality measure often emphasized is "vigour," which is defined as "those seed properties that determine the potential for rapid uniform emergence and development of normal seedlings under a wide range of field conditions." Seedlots with low vigour will result in poor establishment under adverse seedbed conditions such as low temperatures and crusting.

Unfortunately, consistent tests for seed vigour haven't been developed. Accurate seed vigour assessment requires an understanding of the potential causes of seed deterioration for each seedlot. Seed quality loss may be due to:

• immaturity at harvest
• weathering during ripening
• physical seed injury during harvest and transport
• improper storage and overall age

Seed stored at low moisture and temperature will retain vigour the longest. In the above study, one of the certified Westar lots maintained its above average performance over the three years, indicating that a superior seedlot can retain its high yield potential over several years with proper storage. Dr. Bob Elliott of Agriculture and Agri-Food Canada Saskatoon is finishing a multi-year study on seed vigour in canola. Preliminary results indicate that seed vigour is probably best estimated by measuring actual seedling growth. Germination up to five or seven days may also be a reasonable measure of seedlot vigour.

Seed Size

Seed size has been related to subsequent plant development and yield in many crops. However, in canola, research on the effect of seed size on subsequent yield has been contradictory. In a review of seed size research on the prairies, larger seed produced higher yield in five of 11 siteyears. In some cases, larger seed produced more vigorous seedlings, but this advantage wasn't carried through to seed yield. There is good evidence that large seed produces seedlings more resistant to flea beetle attack and thus is higher yielding in situations with flea beetles.

Seed Source

Consider the following factors in seed and variety selection:

• will the variety grow and mature uniformly within the expected growing season
• does the variety have resistance to local diseases
• does the variety have herbicide-tolerant traits that match the anticipated weed spectrum
• does the seedlot have high germination (tested recently) or tests that suggest good vigour
• does the seedlot contain weed seeds not found in your area
• is the seedlot pedigreed to ensure true varietal characteristics
• do the seed bags show signs of improper storage
• does the seed treatment appear uniformly applied

Canola seed quality is affected by the environment under which it was produced. Purchase plump, well matured seed from known suppliers. Seed from a local supplier is less likely to introduce a new weed or disease to your farm.

Date of Seeding

Seeding date affects many aspects of canola growth:

• germination
• emergence
• plant density
• vegetative growth
• time of flowering
• branching
• plant height
• growth rate
• maturity
• yield
• quality

The optimum seeding date for canola depends on many factors such as:

• the earliest date that the field can support tractor traffic, which depends on the amount of snow and runoff, soil texture, spring precipitation and temperature, slope, residue, etc.
• weather pattern for the growing season, including date of last lethal spring frost and first fall frost
• precipitation amounts and timing
• temperature patterns, especially heat stress during flowering and pod filling period
• timing of disease, weed or insect outbreaks
• weed control methods (for example, tillage requirements for conventional seeding or for preemergent herbicides will delay early seeding)
• maturity of different canola species/varieties
• farm and equipment size

Weather patterns vary dramatically across western Canada from year to year and area to area. Conditions in one year may benefit early seeding while the opposite may be true in another year. This variation is evident in research on seeding dates for canola in western Canada. Accurate long-term (several months ahead) weather forecasting for precipitation and temperature for specific areas is not a reality and may never be. Therefore, plan operations based on the most probable growing season weather for the area based on long-term records. This gives the best results over the long term, but may not be optimal for years with unusual weather.

All factors must be considered to identify the seeding date that will produce high yield with acceptable risk. Ensure that the variety chosen consistently matures within the average frost-free period of the area.

Generally, early seeding is desirable. This is especially true in short frost-free areas due to the risk of fall frost damaging yield and quality or in arid areas where high summer temperatures adversely affect flowering and pod development. However, early seeded stands are often thinner due to frost mortality or cold soil conditions that promote more seedling disease. Under cold soil conditions, canola seedlings are also poor weed competitors because of slow growth. For fast germination and emergence, ensure the soil temperature is above 10°C.

A review of 16 different B. napus spring seeding date experiments (total of 70 site years) across western Canada indicates that early seeded canola yields the highest on average. In 55% of the trials, early seeding produced the highest yield, whereas normal seeding dates yielded highest in 30% of the cases. Late seeding produced the highest yield in only 5% of the cases. Approximately 10% of the time, seeding date did not significantly affect yield. The yield advantage of early seeding is supported by crop insurance records. The Management Plus Program in Manitoba shows that seeding B. napus by mid-May produces the highest yields (Figure 1).

Figure 1. Effect of Seeding Date on Crop Yield in Manitoba Based on Crop Insurance Records

In a review of eight B. rapa seeding date trials (total of 32 site-years) across western Canada, there was not a consistent effect on yield. In about 50% of the cases, seeding date did not significantly affect yield. Highest yields were produced about 25% of the time with early seeding, 10% of the time with normal dates, and 15% of the time with late seeding. Although seeding date does not consistently affect B. rapa yield, seed early to avoid midsummer heat stress and to enable early harvest.

The time period defined as "early seeding" depends upon the geographic area. Growers in each area know from experience what is considered early seeding. Soil temperature is not a reliable indicator to start seeding because cold weather often occurs after early seeding. In early seeding risk assessments, consider the probability of severe or sustained cold weather occurring after seeding from local weather records. Although germination begins at soil temperatures around 2°C, there is slow emergence and higher mortality at this temperature (see section on temperature). If soil temperatures are cold during seeding, then other seeding practices (treated seed, pedigreed seed, good seed-soil contact, proper fertilizer placement, correct seeding depth and rate) become even more important. Generally, early seeding is mid- to late April in the Brown and Dark Brown soil zones, the beginning of May in Black and Thin Black zones, and early to mid-May in Dark Grey to Grey soil zones.

The yearly variation in yield with different seeding dates is primarily related to:

• differences in lethal spring or fall frosts
• spring soil temperatures
• crusting affecting emergence
• the timing of rainfall
• stressful periods of hot, dry weather

Early seeding increases the risk of stand loss due to lethal spring frosts, but decreases the risk of yield and quality loss due to fall frost. Experience in most areas indicates that fall frosts are more probable and damaging. As well, spring stands severely damaged by frost still have ample time to be reseeded, which creates more flexibility for growers.

Seeding date also affects maturity. Generally, maturity shortens with later seeding, as illustrated in Table 2 with research from Edmonton, AB and Brandon, MB.

Table 2. Date of Seeding Effect on Canola Maturity at Edmonton, AB and Brandon, MB

Seeding Date	Average Days to Maturity
	Brassica na		Brassica rapa
	Edmonton	Brandon	Edmonton	Brandon
May 1	120	105	98	90
May 7	123	103	94	85
May 15	123	100	90	70
May 21	120	94	89	73
May 30	113	90	89	70
June 7	108	86	87	70
June 12	101	81	85	69

While late seeding reduces the actual number of days to maturity, this usually does not entirely compensate for the late seeding dates. The reduction in maturity is often about half of the delay in seeding. Therefore, late seeded canola matures later than early sown canola (Table 3). Consequently, there is greater risk of frost and weather damage with late seeding. The days to maturity of canola and all crops vary from year to year due to variations in growing degree days and rainfall.

Table 3. Dates of Seeding and Swathing

Seeding Date	Range of Swathing Date
	Beaverlodge*	Edmonton	Brandon
Brassica napus
May 1	Aug. 18-Sept. 14	Aug. 27-Sept. 13	Aug. 12-16
May 15	Sept. 1-19	Sept. 10-26	Aug. 21-26
May 30	Sept. 13-Oct. 2**	Sept. 12-26	Aug. 17-Sept. 7
June 12	Oct. 5-25**	Sept. 16-26	Sept. 10-17
Brassica rapa
May 1	Aug. 5-18	Aug. 9-14	July 29-Aug. 2
May 15	Aug. 11-29	Aug. 12-17	Aug. 2-3
May 30	Aug. 16-Sept. 13	Aug. 21-31	Aug. 4-17
June 12	Aug. 31-Sept. 30	Aug. 29-Sept. 9	Aug. 20-25

* Alberta
** Frozen canola experienced

Optimum canola seeding dates in Ontario are slightly earlier than western Canada-late April to early May. Significant yield reductions occur if seeding is delayed after mid-May. Early seeding in Ontario and the southern parts of western Canada allows the plants to flower before the hot and frequently dry weather in late June and July.

Date of Seeding and Quality

Early seeding generally produces higher quality canola. Late seeding normally decreases oil content levels by 1 to 2% compared to early planting. Oil and protein content often have an inverse relationship, and, therefore, early seeded canola tends to have lower protein. Seeding date also affects oil quality. The oil unsaturation level, which is important to the edible oil industry, increases with early seeding. Specifically, oleic acid increases with early seeding while linoleic and linolenic acids decrease. Also, early seeded canola matures more consistently before fall frost damage and, therefore, the oil has lower chlorophyll content. The time of planting does not significantly affect the erucic acid or glucosinolate content of canola. In years with hot, dry weather in late summer, early seeding can result in lower free fatty acids than later seeding.

Fall Seeding Canola

Seeding a spring canola cultivar in late fall was first studied in the early 1970's at the University of Saskatchewan. The idea was to imitate the observed early germination, growth and maturity seen with volunteer canola. This early emergence and maturity could reduce losses from weeds, diseases, insects, summer drought and early fall frosts. While the early research identified some potential, there were several problems that prevented the widespread adoption. For example, inadequate control of winter annual weeds and fall germination were significant problems.

With the advent of herbicide-tolerant canola, researchers began to re-evaluate fall-seeded canola in the 1990's. More recently, seed coatings with polymers have been developed that show promise in reducing undesirable fall germination. However, preliminary research suggests that polymercoated canola seeded late in the fall under dry fall/ spring conditions can decrease germination and stand establishment.

Research conducted by various agencies over the past decade generally shows a two- to three-week maturity advantage for fall-seeded canola over mid-spring seeding dates, and about one week over early spring seeding. Fall seeded yields tend to be between normal and early spring seeding.

There are several recommendations to capture the most benefit from fall seeding:

Field selection-

Avoid fields with many low spots that flood in spring or windswept slopes with insufficient residue. Avoid summerfallow or heavily fall worked fields, which tend to have more spring crusting problems that will reduce emergence. Avoid fields with residue management problems. Try it on small fields first.

Variety selection-

Unless the field is unusually free from weeds, use a herbicide-tolerant variety since fall seeding stands tend to be thinner and weed control needs to be optimum. Fields with flushing weeds may need multiple herbicide applications and this affects the system choice.

Seeding-

Seed just prior to freeze-up or two weeks prior with polymer-coated seed. Seed to soil contact must be obtained, and try to retain surface residue to prevent spring crusting. However, the residue must be spread evenly. Seed shallow 1.3 cm to 1.9 cm (0.5" to 0.75") and avoid leaving furrows that fill in over winter, increasing the actual seed depth. Avoid broadcasting seed, which tends to increase mortality on the surface. Use typical rates of good quality seed. Fall banding of the fertilizer usually provides the best efficiency and yield response.

Table 4. Advantages and Disadvantages of Fall Seeding Canola

Advantages	Disadvantages
Early maturity which reduces risks of yield or quality damage due to early fall frost. Allows use of higher yielding late maturing species/varieties. Produces bigger seed with higher oil content and allows earlier harvest and marketing.	Untimely germination due to warm weather after fall seeding, or winter Chinooks, causing low spring plant populations. Early spring germinated stands can suffer damage due to subsequent heavy spring frosts. Polymer-coated seeds show promise to reduce the untimely germination but carry extra costs.
Reduced losses due to pests. The early maturity may allow the fall-seeded canola to avoid insect or disease conditions. For example, fall-seeded canola may have less sclerotinia due to shorter, more open canopies and perhaps flowering prior to heavy spore release periods. Preliminary research suggests that fall-seeded canola may have less blackleg. Many canola insects such as diamondback moth and bertha armyworm normally affect yield in mid to late August, and, therefore, early maturing fall-seeded fields may avoid damage.	Increased losses due to pests. The early germinating canola can be more prone to seedling disease complex and flea beetles. In some cases, fall-seeded canola may have more sclerotinia. Early flowering canola may also be more attractive to lygus bugs and the cabbage seedpod weevil.
Early competition with weeds by early germinating canola will reduce losses. Early harvest of fall-seeded crops can provide more post harvest opportunities for weed control.	Sparse stands of fall-seeded canola in the spring can make superior weed control more necessary, resulting in extra costs due to herbicide-tolerant systems, extra herbicides or applications.
Early season moisture utilization provides for better germination and higher yields in certain situations.	Certain fields may not be suitable for fall seeding due to tendency for spring flooding or saturation, frost history and susceptibility to erosion or crusting when residue is limiting.
Workload can be spread out by seeding in late fall rather than the hectic spring period, and by harvesting earlier.	Certain operations may coincide causing time management problems such as fall-seeded canola requiring herbicide application during seeding of spring crops.

Target Plant Populations

Canola is often called a very flexible or "plastic" crop because individual plants can change the number and size of branches and pods in response to available moisture, light and nutrients. Therefore, canola normally compensates for variations in seeding rate or plant population over relatively wide ranges with very little effect on final yield.

At lower plant populations, between plant competition is reduced. Individual plants then grow larger, have bigger stems, branch more profusely and produce more pods that generally extend lower on the plant (Table 5).

Table 5. Plant Population Effect on Canola Plants

	Plants per m2
	60	120	180
Individual plant weight g (oz)	14 (0.5)	8 (0.3)	5 (0.2)
Stem diameter mm (")	8 (0.3)	7 (0.27)	6 (0.23)
Branches per plant:
B. napus B. rapa	5 10	4 8	3 6
Pods per plant:
B. napus B. rapa	90 280	60 180	35 130
Seed yield per plant g (oz)	4.3 0.15 oz	2.2 0.8 oz	1.4 0.5 oz
Seed yield per unit area g kg/ha (bu/ac)	255 2544 (45.4)	260 2595 (46.3)	255 2544 (45.4)

As plant density increases, each plant produces less dry weight, thinner stems, fewer branches, fewer pods and fewer seeds per plant due to increased competition from adjacent plants. However, fewer seeds per plant are offset by a higher number of plants, resulting in a similar seed yield per unit area compared with lower plant populations. Moderate to high plant densities in early growth stages, therefore, can be greatly reduced by frost, hail, diseases or insects, and still produce similar seed yields to undamaged crops.

Research studies on the Canadian prairies have shown that established plant densities ranging from 40 to 200 plants/m² (4 to 19/ft²) often result in similar yields for both species. In a small number of cases, even lower or higher densities have resulted in highest yield. However, very low or high densities also have a risk of significantly lower yield. Therefore, aim to establish plant populations of 40 to 200 plants/m².

Figure 2. General Response of Canola Yield to Plant Population

At very low densities, individual plants may not be able to fully utilize the available light, moisture and soil nutrients, reducing yields. In addition, low densities often mature later and, therefore, have a higher risk of lower quality due to damage from fall frosts. Many research studies were conducted on hand-weeded plots, but commercial fields often have a significant weed load that would likely cause greater yield reductions with low plant populations. Low plant population crops are slower to cover the ground and provide less competition to weeds in the early growth stages while permitting more evaporation of soil moisture. Better weed control with herbicide-tolerant canola systems should allow more stable yield at low densities and provide more growers the possibility of using lower seeding rates.

At high densities, competition between plants results in fewer and smaller pods concentrated on the upper part of the plant. The high position of the seed bearing pods, combined with thinner stems, frequently results in lodging problems, especially with stem diameters less than 6 mm (0.24"). Lodged crops are prone to severe sclerotinia infection. For these reasons, very high densities frequently produce lower yields.

Recommended Seeding Rates

The seeding rate, seed size and germination percentage determine the number of viable seeds planted per unit area.

The actual plant population that becomes established is extremely variable due to:

• strong influences of seedbed firmness
• moisture
• temperature
• soil texture
• depth of seeding
• seed vigour
• amount of fertilizer with the seed
• seed treatment
• insects
• diseases
• other climactic factors

The seeding rate chosen, therefore, depends somewhat upon conditions at the time of seeding.

Canola seedlings experience higher mortality than cereals. Germinated seeds that fail to emerge have been mechanically stopped by soil crusts or killed by disease. Under very good conditions, about 60 to 80% of the seed will produce viable plants in most areas. Under average conditions, about 40 to 60% of the seed sown will produce plants in most areas. In the Peace River region of Canada, only 20 to 40% of B. rapa and 25 to 30% of B. napus seeds can be expected to produce plants. Obviously the level of mortality greatly influences the stand establishment. For example, in a situation where only 40% of the seed produces plants, a 5.6 kg/ha (5 lb/ac) seeding rate of B. napus would place 142 seeds/m² (13 seeds/ft²) of which only 57/m² (5 ft²) would produce plants. In this situation, use a higher seeding rate to achieve a moderate stand density.

Thick canola stands often decrease in density over the growing season due to excessive competition between plants ("self-thinning"). This is another compensation mechanism by canola. For example, a study at the Agriculture and Agri-Food Canada Beaverlodge, AB Research Centre in 1982 found about 35% of a dense B. napus stand had died before maturity, whereas in the following year a thinner stand suffered about 20% postemergence mortality.

Determining a precise recommendation for seeding rate in canola is a difficult task for the following reasons. The information in the section "Target Plant Populations" indicates that canola yields are not highly correlated with established plant density over the many site years of research-there is no "magical" target plant density for highest yield that covers all sites and years. And there is not enough data to determine under which environmental conditions high or low densities are consistently beneficial. Therefore, we can only identify a rather broad range of plant densities to target. Also, the degree of seedling mortality varies greatly from year to year and site to site. In short, we can't predict exactly how many canola plants will emerge or exactly how many we should target.

The most realistic recommendation for canola is a range that normally will provide adequate plant numbers to achieve high yield with minimal risk. Seeding rate outside this range may still produce high yields in some cases but there is also a higher risk of poor yield. A review of 27 seeding rate studies on the Canadian prairies showed that seeding rate was not highly correlated with yield. Of the 65 site-years of data for B. napus, 23 showed no effect of seeding rate on yield, 11 had highest yields with rates lower than 6.7 kg/ha (6 lb/ac), 17 had highest yields with normal rates of 6.7 to 9 kg/ha (6 to 8 lb/ac), and 14 had highest yields with rates greater than 9 kg/ha (8 lb/ac). A similar trend was found in a review of 11 studies of seeding rate for B. rapa: of 30 site-years, 15 cases showed no significant effect on yield; and low, normal and high seeding rates produced highest yields in five cases each.

In most cases on the prairies, growers should seed 5.6 to 9 kg/ha (5 to 8 lb/ac). In Ontario, seeding rates should be 4.5 to 6.7 kg/ha (4 to 6 lb/ac). If seeding less than the recommended rate [for example, 3.4 to 4.5 kg/ha (3 to 4 lb/ac)], for best success look for the following conditions:

• the intended field is relatively free of weeds or treat with an effective herbicide system at early timing
• the seedbed is moist and warm with little crusting potential
• the seedlot is vigorous
• seed placement is accurate and shallow with good seed to soil contact

In contrast, in situations of poor seedbed condition, increase the rate above 6.7 kg/ha (6 lb/ac).

A canola field with low plant density takes longer to close the canopy, allowing more weed growth and soil moisture evaporation. Studies in western Canada have found higher canola yields and lower weed production with higher canola seeding rates in weed competition plots. Therefore, higher rates may be desirable in fields with heavy weed pressure. Higher rates may compensate for low germination seed, cold soil, deep seeding or excessive fertilizer applied with the seed. When seeding on soils with a tendency to crust, higher rates than recommended can be justified. Some growers in the northern areas use higher rates for the B. napus varieties to hasten maturity and facilitate swathing by reducing plant height and the amount of straw that must be handled. However, very heavy stands may increase lodging, especially in the higher rainfall areas, leading to more disease and even more difficulty harvesting.

B. napus seed is large with an average of about 250,000 seeds per kg (115,000/lb), while B. rapa seed is smaller, averaging about 420,000 seeds per kg (190,000/lb). Hybrid varieties of B. napus typically have larger seed size than open pollinated varieties, and have fewer seeds per pound. The approximate number of seeds per unit area and per length of drill row for several seeding rates are given in Table 6.

Table 6. Canola Seeding Rates: Approximate Seeds per Unit Area and Length of Drill Row

Seeding Rate*		Brassica napus-Seeds Per:				Brassica rapa-Seeds Per:
lb/ac	kg/ha	ft2	Yard of Row**	m2	Metre of Row**	ft2	Yard of Row**	m2	Metre of Row**
2	2.2	5	12	57	13	10	22	105	24
3	3.4	8	18	85	19	15	33	158	36
4	4.5	11	24	114	26	20	44	211	48
5	5.6	13	30	142	32	24	55	264	60
6	6.7	16	36	171	39	29	66	316	72
7	7.9	18	42	199	45	34	77	369	84
8	9.0	21	48	227	52	39	88	422	96
9	10.1	24	53	256	58	44	99	475	108
10	11.2	26	59	284	65	49	110	527	121

* 1 lb/ac = 1.12 kg/ha
** Based on 9" row spacing

To calibrate the drill:

1. measure out 30.5 m (100 ft)
2. collect the seed from one drill run over this distance
3. calculate the seeding rate
   
   grams of seed ÷ row spacing
   (inches) x 12 = seeding rate (lbs/ac)
   
   or
   
   ounces of seed ÷ row spacing
   (inches) x 342 = seeding rate (lbs/ac)
   
   or
   
   grams of seed ÷ row spacing
   (cm) x 34.14 = seeding rate (kg/ha)
   
   for example: collect 3.75 g or 0.13 oz
   or
   3.75 ÷ 9" row spacing x 12 = 5.0 lbs/ac
   0.13 ÷ 9" row spacing x 342 = 5.0 lbs/ac
   3.75 ÷ 22.9 cm row spacing x 34.14 = 5.6 kg/ha

This seeding rate would place about 32 seeds/m (30 seeds/yard) of seedrow. Minimize gaps in the seed row. Gaps of a foot or so between plants in a row can result in costly yield reductions.

Seeding Rate Effect on Maturity and Quality

The rate of seeding affects crop maturity. Higher seeding rates produce plants with fewer branches that mature earlier than those at low seeding rates, especially under high levels of nitrogen. In the Peace River region of Canada, an Agriculture and Agri-Food Canada study reported that increasing the seeding rate from 5 to 18 kg/ha (5 to 16 lb/ac) reduced the maturity by five to seven days. A reduction of two to three days in maturity has been reported in the Edmonton, AB and Melfort, SK areas with seeding rate increases from 5 to 12 kg/ha (5 to 11 lb/ac). The seeding rate effect on maturity is more pronounced under cool, late summer conditions than under warm conditions. The slight gain in maturity at higher seeding rates must be weighed against possible increases in lodging and sclerotinia.

Higher seeding rates will have variable effects on oil quality. Research has occasionally found highest oil contents and lowest free fatty acid levels at lowest seeding rates. In cases where high seeding rates decrease maturity enough to avoid fall frost, this can result in reduced green seed and chlorophyll contents compared to low seeding rates.

Reseeding

Each year there are fields that suffer from poor emergence or damage after emergence by frost, hail or insects. The grower often has difficulty deciding whether to replant. To aid in the decision, carefully consider the cause and severity of damage, soil moisture, reseeding costs, potential herbicide residues, and the date. The key question is: will reseeding likely result in greater net income without significantly increasing risk?

The first crucial step in the reseeding decision is to accurately assess the crop injury then estimate the yield potential of the surviving stand. Growers often overrate the injury and thus underestimate the potential of canola seedlings to recover. Canola seedlings injured by hail, wind or frost need several days of recovery before accurate assessments of survival can be made. Severe damage to cotyledon and true leaves that causes yellowing/browning/ blackening does not mean the seedling is dead. A seedling can survive as long as the growing point and the hypocotyl (the stem from the seed to the above-ground growing point) remain intact and turgid. In the seedling stage, canola's small growing point is at the plant tip in the centre between the leaves. After several days of recovery, a small leaf will begin to emerge from the growing point, indicating survival. Also, the stem should have remained turgid and can vary in colour from white to purple.

In years with successive nights of frost, the recovery period may be one week or more from the initial injury before new leaves begin to be noticeable. Seedlings that have been mortally injured will have pinching and browning of the stem below the growing point. In some cases, only the top of the stem is pinched causing the top to lean, but in other cases the whole stem withers and the seedling collapses on the ground. In summary, to assess seedling survival, look closely at the stem for pinching/withering, and look for new growth out of the growing point several days after the last damaging event.

During early growth, most canola stands can sustain substantial seedling mortality without significantly affecting yield due to compensatory branching of surviving plants. Make random plant density counts from the damaged field. The larger the area of damage, the more counts made. If the field is poor due to uneven emergence, then make an allowance for later emerging plants. To justify leaving a poor field, ensure the majority of the field contains the minimum plant number that can produce an acceptable yield. Remember there is no single number that represents a minimum number of plants as growing conditions can have a significant impact on the ability of the plant to compensate.

As a guide, a reasonable threshold is 32 to 43 plants/m² (3 to 4 plants/ft²) for fields with conventional varieties early in the seeding season. However, with herbicide-tolerant systems or late in the seeding season or with dry seedbed conditions, 11 to 22 plants/m² (1 to 2 plants/ft²) can be adequate. Thin stands such as these probably will yield 90% of the normal stand seeded at an early date but will be later in maturity. Crops replanted late in the season typically yield less than earlier plantings that had poor stands. Although some reseeded crops manage to yield the same as very thin crops not reseeded, they incur more costs due to reseeding and, therefore, result in lower net returns. For an example of reseeding yields, see Table 7. In addition, late seeded crops will mature later and thus have a higher risk of fall frost damage.

Table 7. Example of Reseeding Yields with B. napus Canola

Date Seeded	Emergence		Yield
	plants/m2	plants/ft2	kg/ha	bu/ac
May 6	35	3	1456	26
May 18	79	7	1232	22
May 31	70	6	1400	25
May 6, reseeded 31	62	6	1512	27
Least significant difference	17	2	168	3

Farmers in central Alberta experienced a record string of killing frosts in late May to early June, 2000. Seedling canola was severely injured by these frosts and significant reseeding occurred. However, many growers overestimated the mortality and probably reseeded unnecessarily. The following is an actual field situation followed over that growing season. A grower requested the local extension crop specialist to look at a frozen canola stand. The field was seeded in early May to a Roundup Ready B. napus canola, had good straw cover and suffered severe visible damage from the late spring frosts (Figure 3). The producer was not sure if there were enough survivors to produce a reasonable crop and had already reseeded another damaged field. Close inspection of the damaged seedlings indicated that the surviving density was on average 32 to 43 plants/m² (3 to 4 plants/ft²) and about 11/m² (1/ft²) in the worst areas. He was encouraged to leave the field considering the fact that good weed control could be obtained with the herbicide-tolerant system. Continuing frosts hampered the recovery of the canola seedling but eventually new growth appeared after 10 days. The canola stand began to recover slowly over the next few weeks but initially looked quite poor (Figures 4 and 5). By flowering, the stand began to fill in but differences in maturity were evident between areas that suffered different amounts of stand thinning (Figure 6). The stand continued to improve through flowering and pod fill (Figures 7 and 8). The crop matured in September with the thin areas maturing later than the better areas by one to two weeks. Plant counts at harvest averaged 43 plants/m² (4 plants/ft²). The thin crop that was questioned in spring eventually yielded 2,128 kg/ha (38 bu/ac) gross with 2 to 3% green. Although this crop probably would have yielded higher if frost had not occurred, the yield was satisfactory and equivalent or better than reseeded B. rapa canola.

Figure 3. Initial Frost Injury

Figure 4. Recovery Two Weeks after Last Frost

Figure 5. Plant Stand Two Weeks after Last Frost

Figure 6. Recovery by Flowering Stage

Figure 7. Recovery by Podding Stage

Figure 8. Recovery by Ripening Stage

Thus the decision to reseed is often difficult and must be based on thorough agronomic and economic assessments, including accurate evaluation of seedling mortality, surviving stand density, and yield potential of the existing stand versus reseeding.

Seeding Depth

Seeding depth greatly influences the number of seedlings that emerge and their rate of development. Ideally, place canola seed into warm, moist soil with good seed to soil contact. Canola seeds are small with limited energy reserves and, therefore, cannot push to the surface from deep depths. Canola seed sown 12 to 25 mm (1/2 to 1") deep into a firm, moist, warm seedbed germinates rapidly with a high percentage of emergence.

A four-year study at Beaverlodge, AB showed that emergence was highest at the 12 mm (1/2") depth and the rate of emergence was often fastest at the 25 mm (1") depth because of better soil moisture conditions (Figure 9). Rapid emergence of a uniform stand with optimum density will compete better with weeds, develop more leaf and plant growth, yield higher, mature earlier and more evenly.

Figure 9. Effect of Seeding Depth on Plant Density

A review of western Canadian research confirms that the optimum seeding depth for canola is 12 to 25 mm (1/2 to 1")-18 of 25 site years had statistically highest yields for that depth. On average, seeding at 51 mm (2") yielded 10% lower, but in two cases it was 40% lower, which points out the potential for disaster with deep seeding.

Shallower depths may be used if seedbed and moisture conditions are optimum or if the soil is prone to crusting. A firm seedbed is needed to keep moisture around the seed long enough for germination and root growth into stored soil moisture. Excessive tillage frequently reduces establishment of canola on dry soils. Soils worked deep in the spring have dry seedbeds and are often difficult to firm up. This makes it difficult to avoid deep seeding. On sandy soil or in environments where the topsoil dries quickly, seed slightly deeper.

Seeds placed deeply have colder soil to germinate in and further to emerge. Seeds sown 75 mm (3") deep may require three to five days longer to emerge than seed sown at 25 mm (1"). With delayed emergence, there is more opportunity for disease organisms to attack the germinating seedlings. Slow emergence also allows weeds to be more competitive by getting ahead of the slow growing seedlings. Deep seeding also produces plants that flower and mature four to five days later and, therefore, increases fall frost risks. Avoid deep seeding to reach moist soil since canola seeds do not have sufficient stored energy to push their cotyledons to the surface from depths at which cereals are normally sown. If sufficient moisture is not available at the 50 mm (2") depth, seed shallow and wait for rain.

Excessive tillage can create very powdery seedbeds, especially on Grey-Wooded soils and other low organic matter, fine-textured soils. Surface crusting can occur after a heavy rain and can severely inhibit emergence. On soils where crusting is a problem, seed shallow to improve emergence (Figure 10).

Figure 10. Effect of Depth on Emergence in a Grey-Wooded Soil

Finally, measure the seeding depth carefully during the first few passes in a field. Seed depth is the actual depth of the soil over the seed after the opener and packers have passed. Seeding openers that leave a trench or furrow are prone to filling in with soil after rain increasing the true seeding depth. Openers are affected by wear, soil types, moisture and ground speed. Therefore, check the true seeding depth several times in each field or when conditions change.

Broadcast Seeding

Broadcast seeding has gained popularity in certain areas due to the availability of large equipment such as truck floaters with local fertilizer dealers. The speed of seeding, low relative cost to conventional seeding and the ability to seed on fairly wet fields makes this practice attractive. However, broadcast seeding usually performs poorer than placing the seed uniformly at a 13 to 25 mm (1/2 to 1") depth. In 18 site-years of research on the prairies, broadcast canola seeding was inferior to 25 mm (1") drilled seeding nine times, and superior only twice. Overall, broadcast seeding yielded 5% less than drilled seed, but in several cases the yield loss was 20%. This indicates that broadcast seeding is a higher risk practice than drilled methods. In Grey-Wooded soil prone to crusting, broadcast seeding has sometimes been superior to drilled seed.

In order to avoid disasters with broadcast seeding, the following factors are important. The soil must be firm before broadcasting. This allows the seed to be placed relatively shallow during the subsequent incorporation. Broadcasting into a loose, fluffy seedbed causes a wide range of final seed depths and rapid drying of the loose layer. The result is uneven germination. Shallow pre-seeding tillage will help maintain the seedbed firmness and moisture.

Good soil moisture, especially following seeding, is required for broadcasting to be successful. Packing after the seeding incorporation may improve the success of broadcast seeding, but use caution with low organic matter soils that are prone to crusting. Post-seeding rolling can increase wind erosion and seedling damage. If mixing canola with a fertilizer formulation such as 11-51-0 for seeding through a fertilizer attachment, only do so immediately prior to planting. Experience has shown that seed viability is not extensively damaged if seeding is delayed for a few days due to adverse weather, provided the mixture is stored under dry conditions.

Row Spacing

Seed row spacing is the distance from the centre of a seed row to the centre of the adjacent one. This can be confused with seed row width, which is the distance across an individual seed row and, therefore, indicates how wide the seed is scattered in each row. Seed row scatter width affects the impact of row spacing-more seed scatter reduces the gap between rows. A better method to describe seed row spacing and seed row scatter width is seedbed utilization (SBU). SBU is the ratio of seed row scatter width to row spacing-for example, a 7.5 cm spread on a 23 cm row spacing (3" spread on a 9" spacing) gives a 33% SBU.

In theory, narrow row spacing should produce highest yields for several reasons. Planting patterns that create an equal distance between all plants (in rows and between rows) will produce the least competition between crop plants for water, light and nutrients. Also, equidistant crop patterns maximize the competition with weeds. Wide row spacings often result in higher mortality within the row and lower overall plant densities. The higher competition between plants within rows on wide spacing can lead to thinner stems and increased lodging. Reducing gaps between seed rows will reduce soil moisture losses by evaporation before canopy closure.

In the past, the majority of canola in Canada was planted with disc or hoe press drills with row spacings varying from 15 to 30 cm (6 to 12") and fairly narrow row widths. Research on the prairies during the conventional tillage era showed that narrow row spacing was beneficial. Over 15 site years, the narrowest row spacing consistently produced the highest yield. The yield increase with row spacing narrower than normal 15 to 23 cm (6 to 9") ranged from 10 to 30%. Figure 11 illustrates the effect of row spacing on canola yield under conventional tillage from a four-year study in Saskatchewan.

Figure 11. Effect of Row Spacing on Canola Yield Under Conventional Tillage

The introduction of pneumatic seeding equipment (air seeders/drills) and direct seeding changed things and reignited the controversy over row spacing. Pneumatic seeding equipment became predominant in the 1990's due to improved capacity, transportability and adaptability for direct seeding. The retention of residue for soil conservation creates clearance problems in seeding equipment and sparked interest in wide row spacing. Wide row spacing also reduces machinery costs and draft requirements. In addition, the residue layer between seedrows in directseeded systems influences soil moisture evaporation, weed germination and growth, and could affect the optimum row spacing. However, wide row spacing can increase injury from excessive amounts of seed placed fertilizer, and create lower emergence rates.

Recent research on row spacing with modern equipment and conservation practices suggests that optimum row spacing may be wider than in the past. Similar yields were reported in 12 of 15 site years of research during the 1990's that compared 15 to 30 cm (6 to 12") spacings in directseeded systems. Very wide spacing of 41 cm (16") produced lower yields in five of 12 site years, and was 10% lower yielding on average. However seven of the site years involved broadcast nitrogen to avoid seed row toxicity and this probably negatively affected the performance of wide row spacings. New seeding openers with band placement near the seed row would reduce the weed access to the fertilizer and may improve crop yields under wider spacings. For example, canola yields under 30 cm (12") row spacings were found to be statistically similar to 23 cm (9") (13 of 15 site years) by Agriculture and Agri-Food Canada researchers at Melfort, SK, Beaverlodge, AB and Brandon, MB using side-banded N placement. In contrast, recent research at Lethbridge, AB, Blackie, AB and Edmonton, AB showed an emergence and yield benefit with narrow rows under direct seeding and side-banded N at two of the sites. A wide row width or seed scatter would also help offset negative consequences of wide row spacings. Figure 12 illustrates the effect of row spacing on the yield of direct seeded canola with broadcast nitrogen (from Canola Council of Canada Crop Production Centre reports).

Figure 12. Effect of Row Spacing on Direct-Seeded Canola Yield

Coated Seed

Coated seed is pedigreed canola treated with fungicide and possibly an insecticide, usually some phosphate and lime, and an outside protective coating. Coated seed is normally 25% larger in size than uncoated seed. Consequently, the use of coated seed can make it easier to accurately adjust the seeding rate, a problem with older equipment. However, because of the significant difference in coated seed size, it is important to adjust the seeding rate and accurately calibrate equipment to ensure that the desired number of seeds is seeded.

Trials measuring yield response to coated seed have demonstrated a slight yield advantage. In a review of 44 trials in western Canada, coated seed produced higher yield in 28 cases, similar yield in 10 cases, and lower yield in nine cases. Overall, coated seed produced 7% higher yield than normal treated seed. Perhaps the most significant advantage to coated seed is the reduced dust and increased safety because the coating reduces user contact with fungicidal or insecticidal seed treatments. However, higher seed cost is a disadvantage for coated seed.

References