As farmers are getting into full spring planning mode, it’s important to review the factors involved in getting a successful canola crop established.
There’s been lots of good research published by Neil Harker and colleagues from Agriculture and Agri-Food Canada Lacombe and corroborated by research and demonstration trials conducted by others such as the Canola Council that generally indicate the advantages of earlier seeding of canola. The sooner that crop comes out of the ground, the sooner it can start its life process and then can beat some of the common seasonal stresses such as heat stress during flowering in mid summer and the risk of fall frost.
But the critical point to remember, and one that I always like to stress, is that it’s not the date by itself that the crop is seeded that’s important, but rather it’s when that seed comes out of the ground that’s critical.
Seeding a crop in April or early May when conditions are cold, and especially if done in a hurry, will generally not do that seeded crop much good. What good is it to seed early and in a big hurry (other than bragging rights at the local coffee shop!) if that seed ends up sitting in the ground for three to four weeks or longer before it comes out of the ground, all the while susceptible to seedling blight, seed rot and other factors.
Remember, that seed doesn’t begin to work for you and until it emerges and begins the process of photosynthesis. Before that, it’s living mostly off the energy contained in that seed, so anything you can do to reduce the energy expended in getting the crop out of the ground will generally help you in getting a robust and healthy plant out of the ground, one that’s better able to take advantage of the available growing season and also more capable of rebounding from early season stresses such as flea beetles and spring frosts.
The important point to keep in mind isnothow early can or should I seed this canola crop, it’s what can I do to get it out of the ground as soon as possible, so that I can get that plant working for me. Remember, it’s not when the canola goesinto the ground that’s important, it’s when and how it comesoutof the ground that’s important. So let’s review a number of factors involved in getting your crop out of the ground as soon as possible.
First of all, probably the most critical factor is soil temperature. Soil temperature drives all metabolic processes and although many of the other factors such as moisture, aeration, nutrition and depth are also important, they do not begin to influence the seed until it’s warm enough to start all the biochemical processes of seed germination.
Figure 2 on page 4 from the Canola Growers Manual (Canola Council of Canada, www.canolacouncil.org/canola_growers_ manual. aspx) illustrates the role of temperature on the speed and rate of canola germination.
You can see from the table, that at a temperature of 2 C, it takes almost 12 days to get 50 per cent of the seeds germinated, whereas at a temperature of 6 to 8 C, 50 per cent germination is achieved at only three to four days and that 100 per cent germination is achieved by eight days. Obviously those extra days in the ground mean that that germinating seed is more prone to damage from diseases and insects.
This is why there is the general recommendation to not start seeding canola until the soil is at least around 5 C. Early seeding is important, but only when the soil is warm and capable enough of supporting rapid growth. Some years we get an early and warm spring and the soil may be a 5 C or better in early April. Does that mean I should start seeding my canola? Well only if you feel that the chances of getting a significant frost are low. With the high cost of canola seed these days, the economic risk of having to reseed is much higher when seeding so early in the season, so keep that in mind as well. Soil temperature is critical, but look at it through the lens of the calendar date as well.
Secondly, moisture is also critical in germination. Soil moisture affects how quickly water penetrates the seed. Canola seed has to imbibe a high percentage of its weight in water before germination begins.
The more moisture that’s available, the quicker the seed will be able to imbibe enough moisture for germination. Having adequate moisture in terms of stored soil water and early spring precipitation play a large role in successful and rapid germination. But other soil factors such as soil type also have a role to play. Soils that hold more moisture (such as clays) generally have more rapid seed imbibition and germination than soils that hold less moisture such as sands. This is illustrated in the following table, also obtained from the Canola Growers Manual.
However, having free water by itself in the soil is not essential for germination. As long as there is enough soil moisture to maintain a relative humidity in the soil pores of 60 to 75 per cent, the canola seed coat will continue to absorb moisture. It’s critical to maintain that soil moisture through germination and emergence by maintaining a firm seedbed and reducing the amount of moisture loss from the seedbed. Factors such as adequate packing after seeding, soil particle sizing and residue and stubble management can have a large bearing on how quickly moisture is lost from the soil surface.
Another factor that can affect the amount of water available for germination is the type, amount and placement of fertilizer. In general, fertilizers placed very close to or with the seed will reduce the amount of moisture available for seed germination because these fertilizers end up using some of the available moisture to dissolve the fertilizer and bring it into solution. Also, the “salt effect” of different fertilizers has a role in “tying up” the available moisture. In general, one should avoid placing large amounts of fertilizer with the seed, especially with nutrients that are generally more mobile such as nitrogen and sulphate.
Seed-placed fertilizer should be left for less mobile nutrients such as phosphorus and to a lesser extent, potassium. Put the other more mobile nutrients in a band further away from the seed to reduce the amount of moisture tie-up by the fertilizer interfering and reducing the amount of moisture available for germination by the seed. Or in the case of nitrogen, if you want to put larger amounts of seed placed urea, consider using ESN (Environmentally Smart Nitrogen) urea that is coated with a polymer to meter the rate of diffusion from the fertilizer granule, which in turn will reduce the amount of moisture tie-up by the fertilizer and also reduce the amount of ammonia toxicity to the germinating seed.
The major nutrient that’s critical for early seedling growth is phosphorus (P). Since it’s one of the least mobile nutrients, its critical that enough phosphorus is available with or very close to the seed to enhance early seedling growth. This is especially true when soil temperatures are cool which also regulate the rate of chemical reactions in the soil as well biological processes such as seed germination. The amount of seed placed phosphorus required depends largely on the available soil test levels.
If the inherent phosphorus fertility of the soil is good through the use of adequate or generous amounts of applied phosphorus fertilizer in past years or from the proper use of manure, then the amount of seed placed P is less critical. But, if available soil P levels are low, then one needs to apply at least 15 to 20 pounds of phosphate with or very close to the seed. More phosphorus than this may be required for optimum yields, but one then has to look at either modifying the seed opener/placement system to use a higher row-width utilization (RWU) of a single-shoot opener or to the use of double-shoot openers. RWU (also often referred to as SBU or seedbed utilization) is defined as the seed opener spread width divided by the seed opener spacing multiplied by 100. For example, a seed opener that places the seed (or seed-fertilizer mix) in a one inch spread using a seeder that has a 10-inch opener spacing will have a RWU of 10 per cent (1/10 x 100).
DEPTH OF PLACEMENT
Seeding depth is the next factor that’s important in rapid and even germination. Canola is a small seed with limited resources, so it does generally does not do well with deep seeding. In general, canola responds best when seeded at a depth of one half to one inch into a firm, warm and moist seedbed. The role of seed depth is illustrated in Figure 1 at right (from the Canola Growers Manual).
Shallower depths may be considered if soil moisture conditions are optimum or if the soil is prone to crusting. Alternatively, if soils are sandier, deeper depths may be considered since sandy soils hold less moisture than clay soils and will dry out faster and also, sandier soils pose less physical restriction to emerging seedlings.
Seeding depth is also influenced by the uniformity of depth. Uniformity refers to how close are all the seeds at the desired depth. One may have two fields, both seeded at an average seed depth of three-quarter- inch. But in one field, the actual seed depth may range from one-tenth to two inches whereas in the second field, the range may be from one-half to one inch. Obviously the second field seeding depth is much more uniform and will emerge more uniformly than the first field. Field levelness also influences the uniformity of depth especially with seeding equipment that do not use independently controlled openers. Judicious use of harrows can be used to level of furrows left from the previous year and improve field levelness.
Also, trash or residue management can have a large role in seed uniformity and subsequent germination. Residue that is evenly distributed enhances the evenness of germination of subsequent crops. The use of proper straw choppers on combines that spread both straw and chaff over the width of the combine swath go a long way in reducing any subsequent residue problems. Secondly, the judicious use of heavy harrows to spread residue can be useful in some situations.
Also, under some really heavy residue conditions, consider baling off the straw to reduce problems with germination of the subsequent canola crop.
Also seeding speed has a large role in seed uniformity. I often get asked, “What is the ideal seeding speed?” The ideal seeding speed depends on a number of factors including field uniformity, soil type, opener type and style. Obviously smoother fields can be seeded at a faster speed than rougher fields. Openers that throw soil less can be seeded faster than openers that throw soil more and the amount and type of residue have a role in how fast one can seed.
Also, whether one is using a single-shoot or double-shoot opener can be affected by speed. Double-shoot openers rely on the opener structure and geometry to ensure the desired seed to fertilizer separation and these openers may work up to a certain speed, then tend to destroy the separation once a certain speed is exceeded. This is all dependent on the opener type and the various soil factors such as texture, moisture, organic matter, residue, etc.
The best thing is to try this out on your own field. Do a few passes at your regular or normal speed. Then do an adjacent pass or two at a speed one mile per hour slower than your usual speed. Then do a pass or two that is one mile per hour faster than your usual speed. Then do a plant count comparing the number and size of the plants seeded at the different speeds shortly after the crop has emerged. The you will get an accurate assessment on the role of seeding speed on your own farm, under your own actual conditions.
To sum things up, it’s not so critical when your seed goes in to the ground. It’s much more critical when and how it comes out of the ground. Keep these various factors in mind as spring progresses, as you may need to consider to enhance the speed and uniformity of canola germination on your farm.
JohnMaykoandhisfamilyfarmnear Mundare,Alta.,andhasspentover20years developinghiscanolaproductionexpertise
6 Days After Seeding 13 Days After Seeding
Figure 1. Effect of Seeding Depth on Plant Density
Figure 2. Effect of temperature on germination of B. napus
Sylvania Sandy Loam 33 50