Seed and Fertilizer Placement

Table of contents

    Important tips for best management

    • Canola seed is small and sensitive to deep seeding. Canola emergence and seedling survival tend to be higher and more uniform with seeding depths of 12 to 25 mm (1/2” to 1”) into a warm, moist firm seedbed. Broadcasting seed on the surface is less reliable due to the potential for poor seed to soil contact, drying of surface soil leaving inadequate moisture for germination, and poor consistency of seeding depth if incorporated.
    • Canola seed is sensitive to seed-placed fertilizer, particularly nitrogen and sulphur. Safe rates of seed-placed nitrogen may be as low as 10 kg/ha (10 lb./ac.) depending on row spacing, seed and fertilizer separation in the seed row, soil moisture conditions, and soil type. While some seed-placed phosphorus (up to about 20 kg/ha) improves seedling vigour on deficient soils or under cool soil conditions where availability is reduced, higher rates or combinations with other nutrients may increase seedling mortality, especially in dry conditions. Ideally only a safe amount of phosphorus should be placed in the seed row, with all other nutrients banded away from the seed.


    Seeding depth influence on plant populations

    Canola seed sown 12 to 25 mm (1/2” to 1") deep into a firm, moist, warm seedbed germinates rapidly with a higher percentage emergence.[1] Rapid emergence of a dense uniform stand produces a crop that will compete better with weeds, yield higher, and mature earlier and more evenly.[2]

    Figure 1. Seeding depth effect on plant emergence

    Seeding shallower than 12 mm (1/2”) may work if seedbed and moisture conditions are optimum but extreme temperature and moisture fluctuations in this region can make it a challenging place for germinating seeds to sustain life. Seeding ultra-shallow can be risky if soil conditions are not watched closely and the seeding tool is not properly maintained for evenness of seed placement.

    Seeds sown 75 mm (3") deep will require several days longer to emerge than seed sown at the recommended 12 to 25 mm (1/2 to 1"). Seeding 75 mm (3”) deep will also reduce seedling survival rates because canola seeds often do not have sufficient stored energy to push their cotyledons to the surface from that depth. As a result the stand produced will tend to be patchy and non-uniform. With delayed emergence:

    • there is more opportunity for disease organisms to attack the germinating seedlings
    • plants that emerge from deep seeding are stressed and are usually more susceptible to additional stresses
    • insecticide seed treatments may be near the end of their effectiveness when plants are most vulnerable
    • uncontrolled weeds get ahead of the slow growing seedlings
    • canola matures later or unevenly, which increases fall frost risks


    Seeding into moisture:
    Moisture is essential for germination and emergence, but seeding deep to reach moist soil should be avoided early in the season when soils are cool. If sufficient moisture is not available at the 50 mm (2") depth, growers are likely better to either wait for rain before seeding or to keep seeding depth shallow to allow good emergence when rain comes, hopefully in the near future. Remember that seeding will open the soil and dry it out further, and the deeper you seed, the more rain will be needed to seep down to contact the seeds. If soils are warm and seeding dates are pushing towards the end of May, seeding deeper to reach moisture can be a management strategy to get a stand established. Rain in the near future is still essential in this scenario.

    With light sandier soils that are prone to drying out quickly, seeding slightly deeper may be a benefit to germination. However, use an adequate emergence percentage when calculating seeding rates to achieve target populations of at least 50 plants per square metre (5 plants per square foot), especially in cool soils where mortality can increase.

    Seeded 1" deep (l) vs. 3" deep (r)

    Limit seed-placed fertilizer

    Salts in fertilizers can desiccate canola seedlings. Nitrogen fertilizers also cause significant damage through ammonia toxicity. Placing high rates of fertilizer in the seed row often leads to serious damage or death of seedlings.

    Ammonium sulphate (21-0-0-24) and potassium chloride (0-0-60) have higher salt indexes than other fertilizers. Phosphate has a lower salt index, but common phosphorus fertilizers are combined with ammonium (monoammonium phosphate, for example), and it’s this nitrogen component that provides the greatest limitation on safe rates of seed-placed phosphate fertilizer product.

    Putting down seed and all fertilizer in one pass is common practice on the Prairies, but for canola, most of that fertilizer has to go in a side band or mid-row band to avoid significant seed damage and seedling mortality. Table 3 shows safe rates of seed-placed urea, given in pounds of actual nitrogen per acre. (Multiply by 0.46 to get pounds of urea.)

    Safe rates of seed-placed nitrogen vary depending on opener width, row spacing, soil type and moisture conditions. For example, safe rates are 11 kg/ha (10 lb./ac.) for canola when using a 25 mm (1”) knife on 23 cm (9”) row spacing in medium textured soils.[3]

    Safe rates increase when openers spread seed and fertilizer over more of the seedbed and when seeding into heavy soils. For example, when seeding into clay soil with a 75 mm (3”) opener on 23 cm (9”) row spacing, the safe nitrogen rate can be as high as 45 kg/ha (40 lb./ac.)[3]

    Remember, when using wider row spacing, seed and fertilizer concentrations in the seed row increase, so wider row spacing will mean lower safe rates of seed-placed nitrogen. This is discussed in more detail later in this chapter.

    As shown in the table below, 'Guidelines for nitrogen placement with canola', Manitoba has lower safe rates than Saskatchewan and Alberta. This distinction is based on soil characteristics. Manitoba soils tend to have high soil pH, and high levels of free lime or carbonates. Under these conditions, urea tends to release more of its nitrogen in the free ammonia form (NH3), which is more damaging than the ammonium form (NH4).

    When selecting seed-placed nitrogen rates, note that the rates in the guidelines table below assume that the grower is already applying a safe rate of seed-placed MAP (11-51-0 or 12-52-0). MAP is usually safe at rates below 45 kg/ha (40 lb./ac.), or 22 kg/ha (20 lb./ac.) of actual phosphorus. Some growers also use diammonium phosphate (DAP) for starter phosphorus, but this form has a higher nitrogen component. Safe rates of seed-placed nitrogen will be lower if the grower is using DAP instead of MAP.

    Table: Safe levels of seed-placed nitrogen

    Factors that affect safety of seed-placed nitrogen

    Soil texture: The lighter the soil texture, the higher the risk of reduced emergence, low plant populations and yield loss. Clay soils hold more nitrogen in the ammonium (NH4) form. In sandy soils, more ammonium converts to ammonia, which is the form that causes seed and seedling damage.

    Seedbed moisture conditions at seeding: With moist soil conditions, water dilutes the concentration of nitrogen molecules around the seed and seedling. Water also disperses nitrogen molecules throughout the soil, reducing concentrations around the seed. In dry conditions, seed-placed nitrogen fertilizer tends to produce higher concentrations of ammonia and ammonium that can damage young seedlings. Seed-placed nitrogen rates should be lowered when conditions are drier than normal.

    Fertilizer source: Ammonia is the most damaging form of nitrogen. That is why anhydrous ammonia should never be placed in the seed row. A product such as polymer-coated urea can allow for higher safe rates of seed-placed nitrogen as compared to urea. Even with safer nitrogen products, not all of canola’s nitrogen requirement can be safely seed-placed.

    Row spacing: Wider row spacing increases the risk to harming seedling emergence and yield potential, assuming that fertilizer rates per hectare (or acre) stay the same, because the concentration of fertilizer within each row is increased.

    Application rate: The higher the nitrogen rate, the higher the risk to seedling emergence and yield potential when nitrogen fertilizer is placed in the seed row.

    Crop type: Generally, small seeded crops such as canola are more sensitive to seed-placed nitrogen. Do not use the same seed-placed fertilizer rates for canola as for coarser grains such as wheat, which are generally less sensitive to ammonia toxicity and salt effect.

    Soil pH: Safe rates are lower in high pH soils. At higher pH, more of the N from urea is in the free ammonia form (NH3) vs. ammonium (NH4). Ammonia is more damaging.

    Polymer-coated urea

    Polymer-coated urea, such as ESN can increase the safety of seed-placed urea. This product slows the release of ammonia and ammonium from urea fertilizer, which increases seed safety and allows for higher rates of nitrogen to be placed with the seed.

    ESN coats urea prills in a polymer that lets water in slowly, and then slowly releases ammonia and ammonium back out into the soil. This keeps the concentration of ammonia and ammonium lower early in the season when seedlings are most sensitive. Safe seed-placed rates of ESN can be 3 or more times higher than provincial recommendations for straight urea depending on opener and seeding tool.[4] [5] [6]

    Evaluating placement in the field

    Measure depth carefully during the first few passes seeding a field. Seed depth is the actual depth of soil over the seed after the opener and packers have passed. Openers that leave a trench or furrow are subject to filling in with soil after rain, which may increases the true seeding depth. Opener wear, soil type, soil moisture and ground speed will influence opener performance. Therefore, check the true seeding depth several times in each field or when conditions change.

    Influence of row spacing

    Seed row spacing is the distance between the centre of one seed row and the centre of adjacent rows. Seed row width is how wide seed is scattered in each row. Seed bed utilization (SBU) is based on both of these measurements. SBU is the ratio of seed row width to seed row spacing. For example, a 7.5 cm seed row width — also called “spread” — on a 23 cm seed row spacing (3" spread on a 9" spacing) gives a 33% SBU.

    The “best” seed row width depends on a grower’s overall system. A narrow row spacing will have lower seed and fertilizer concentrations in each row than the same rates in a wider row spacing. (That’s because the same seeding rate per acre applied to more rows per acre means fewer seeds per row). An Agriculture and Agri-Food Canada study found that air seeder row spacings of 23 cm (9”) and 30 cm (12”) had higher yields, in general, that wider spacings of 45 cm (18”) and 60 cm (24”). [8]

    Factors to consider when choosing row spacing:

    • Narrow row spacing may reduce soil moisture losses by evaporation because canopy closure will be somewhat faster.
    • In a no-till system, growers may find that wide row spacing can reduce crop residue buildup between the drill shanks, improving seeder performance. Wider rows (fewer openers) also reduce machinery costs and draft requirements. In direct seeding systems, the residue layer between seedrows may also reduce soil moisture evaporation, weed germination and growth.
    • As noted earlier in this section, wide row spacing can increase injury from seed-placed fertilizer, due to the higher fertilizer concentration in the rows resulting from the reduced seedbed utilization. Safe seed-placed fertilizer rates are lower with wider row spacing.
    • Openers that place fertilizer in a band placement near the seed row (not in the seed row) may improve crop yields for row spacings of 30 cm (12”) or wider.[7] [8]
    • Wider row spacing tends to delay the day of first flower, extend the flowering period, and increase lodging. These can all contribute to later maturity, which increases the risk of frost damage and quality loss, even if yield potential stays the same.[8]
    • Wide row spacing combined with high seeding rates could lead to ‘self-thinning’, where seedling survival is decreased due to overcrowded seeds in-row competing for resources.
    • A narrower row spacing will have improved crop competition with weeds and decreases the reliance on herbicides for weed control.

    Check opener performance. An opener may claim to provide separation between seed and fertilizer, but opener wear, seeding speed, fan speed, and soil conditions can result in the targeted separation between seed and fertilizer not actually being achieved. Check that the opener is placing seed and fertilizer where expected, attaining adequate  separation.

    Broadcast seeding

    Broadcast seeding is occasionally used in some regions but it should be considered a last resort for when ground conditions prevent effective seeding with a seed drill or planter. Truck floaters or other granular spreaders (Valmar for example) can sometimes cover a field when heavier equipment can’t, or when openers can’t perform properly because the soil is too muddy. Properly applying fertilizer when broadcast seeding may also be an issue. Speed of seeding and low relative cost compared to conventional seeding also make broadcast seeding an attractive option for some, but this remains a high risk option for seeding canola.

    When it comes to yield, broadcast seeding usually performs poorer than placing the seed uniformly at a 12 to 25 mm (1/2 to 1") depth. In 18 site-years of canola seeding research on the Prairies, broadcast 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.[9]

    Tips for broadcast seeding:

    Be patient. Seeding any time before the end of May should give canola a good chance to achieve its full yield potential. Before rushing to broadcast, there may be an opportunity for improved field conditions to allow drill seeding. By late May if broadcast seeding still appears to be the best solution for some growers faced with continued wet fields, warmer soils should allow more rapid germination and establishment of the seedlings with less risk of mortality from cool soils or frost damage, or stranding on the surface.

    Increase the seeding rate. Seed germination and seedling survival for broadcast canola could be lower compared to seed drilled into a moist, packed seedbed. A higher seeding rate can compensate for this higher seed mortality. It also provides more margin for error if the seed and fertilizer ratio doesn’t stay consistent as the floater tank empties. A floater with two tanks, one for seed and one for fertilizer, should eliminate this particular risk. Consider seed size (in grams per 1,000 seeds, or TSW) and estimate seedling survival when setting the seeding rate by using the tools at www.canolacalculator.ca.

    Adjust fertility practices:

    • Double the phosphorus rate. Canola plants need early access to phosphorus. When broadcast, phosphate prills and seed are not always close enough for timely access to the fertilizer. Higher phosphate rates and seeding rates will improve the average proximity of seeds to fertilizer prills. Jumpstart, the seed-applied biological phosphorus enhancer, may help.
    • Account for higher nitrogen losses. Broadcast nitrogen has a higher risk of denitrification when applied on saturated soils, reducing N fertilizer efficiency. Enhanced efficiency nitrogen fertilizers could help to reduce these losses. Adjust fertilizer rates accordingly, but keep in mind a realistic target yield based on the time of year and field conditions.
    • Seed soon after blending. If you plan to pre-blend seed and fertilizer prior to the floater arriving, note that fertilizer, especially any kind of nitrogen fertilizer, has the potential to reduce canola seed germination rates. Apply the blended seed and fertilizer as soon as possible after blending or utilize a floater with two tanks, one for fertilizer and one for seed, which eliminates the need for blending.
    • Consider a split fertilizer application. Growers could broadcast their seed first, then top up with appropriate forms of nitrogen and sulphur if the crop gets established. However, early access to nutrient is important for optimal yields, so top dressing applications should be made as soon as possible after emergence. Four to five plants per square foot can be enough for canola to reach its yield potential, but even two plants per square foot can produce a decent yield.
    • Broadcast N and S, then drill seed. If the key barrier to using the drill is the risk of getting stuck when pulling a fully-loaded cart, growers could broadcast their nitrogen and sulphur, and use the drill just for seed and starter phosphorus. That way, they wouldn’t have to fill the seeder tank right full, which could make it possible to get the drill through a field without getting stuck. If nitrogen is broadcast, always use a product to reduce nitrogen losses.


    Cultivate or harrow after seeding.
    Shallow cultivation or harrowing (if cultivation is impossible due to wet conditions) will help improve seed to soil contact in a field that has been broadcast seeded. Avoid creating lumps or clods during cultivation or straw piles with harrows or cultivators.

    High residue increases risk. Broadcasting onto fields with high residue and a loose, fluffy seedbed may not provide the seed to soil contact for high establishment rates. But cultivating these fields ahead of broadcasting could create an equally inhospitable seedbed, with large clods and a crusted soil surface.

    Careful with weed control timing. Seeds on the soil surface are highly vulnerable to herbicide. Do not apply post-seed glyphosate on Liberty Link and Clearfield canola varieties that have been broadcast and remain on the soil surface. Roundup Ready varieties, however, can tolerate glyphosate at this early stage.

    Crop insurance depends on establishment. Broadcast canola may not automatically qualify for crop insurance. Rules for unseeded acreage benefits vary by province. Growers should consult with their insurance representative to ensure they understand these rules clearly before making a final decision on trying broadcast seeding.

    Aerial seeding

    No studies have looked at seeding canola by plane. It has been done in very wet springs, but if growers have to seed by plane because the field is too wet for a broadcast floater, that means it’s probably also too wet for weed control, fertilizing and harrowing — each important to a profitable broadcast canola crop.

    Fields too wet for ground equipment have probably been wet for a month or more. That means most of the nitrogen reserves have likely been lost. Since fertilizer is too heavy to apply efficiently by plane, the canola seeded by plane will not get a nutrient top up until the ground is firm enough for ground equipment. Canola needs nutrients early in the season to reach its full yield potential.

    Canola emerging in wet soil will also be oxygen deprived. This is not a hospitable environment for seedlings. Seeds may germinate, but the roots will likely die unless soil conditions improve quickly following seeding.

    Growers should consider all agronomic and logistical challenges before attempting to seed aerially.

    References

    [1] A four-year study at Beaverlodge, Alta., 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).

    [2] A review of western Canadian research confirms that the optimum seeding depth for canola is 12 to 25 mm (1/2” to 1"). Eighteen of 25 site years had statistically highest yields for that depth. On average, seeding at 50 mm (2") yielded 10% lower, but in two cases it was 40% lower in yield, which points out the potential danger with deep seeding.

    [3] Saskatchewan Ministry of Agriculture, Manitoba Agriculture Food and Rural Initiatives.

    [4] A nine-site Alberta study, led by Alberta Agriculture in Lethbridge, is looking at canola stand establishment and yield for seed-placed ESN compared to seed-placed untreated urea. The researchers have completed only three of the four years and the study results are not yet published, but so far it appears that ESN provides a significant improvement in seed safety with higher rates of seed-placed nitrogen. The study found that ESN applied at 136 pounds per acre (60 pounds of actual nitrogen) could be safely applied in the seed row. This is based on 10% seedbed utilization.

    [5] “Improving Effectiveness of Seedrow-Placed N with Polymer-Coated Urea (ESN) for Emergence, Yield and N Uptake of Canola and Wheat”  (Unpublished Results) S. S. Malhi, Agriculture and Agri-Food Canada, Melfort, Sask. Abstract: Seedrow-placed urea minimizes soil disturbance in reduced tillage systems, but it generally decreases emergence at nitrogen (N) rates adequate for optimum crop yield. Two 3-year field experiments (2007-2009) were conducted on canola (Brassica napus L.) and wheat (Triticum turgidum L.) on a thick Black Chernozem silty clay loam soil at Melfort Research Farm, Saskatchewan, Canada, to determine the influence of N rate (40, 80 and 120 kg N ha-1), N source [(untreated urea (urea) and polymer-coated urea (ESN)], and placement (side-banded N and seedrow-placed N, using knives to create 2 cm wide bands), plus a zero-N control, on seedling emergence, seed and straw yield, protein concentration (PC) in seed, and N uptake in seed and straw. For both crops, side-banded N had no detrimental effect on seedling emergence compared to the zero-N control for all rates and sources. Conversely, seed-row placed urea reduced seedling emergence for wheat at the 80 and 120 kg N ha-1 rates and reduced canola seedling emergence substantially at all rates, but particularly at the 80 and 120 kg N ha-1. Seed-row placed ESN had little or no effect on seedling emergence of wheat or canola. Seed yield and N uptake were generally greater with ESN than urea, when the fertilizers were seedrow-placed at high N rates. The findings suggest the effectiveness of ESN in providing greater N application options for producers.

    [6] Agrium’s ESN label says it can be applied at 3X the suggested safe N rate when using 100% ESN as the N source.

    [7] Agriculture and Agri-Food Canada researchers at Melfort, Sask., Beaverlodge, Alta., and Brandon, Man., found canola yields under 30 cm (12") row spacings were statistically similar to 23 cm (9") when using side-banded N placement. A wide row width or seed scatter would help offset negative consequences of wide row spacings.

    [8] Kutcher et al. See poster called “Kutcher poster 4” in the seed and fertilizer placement folder. A study by AAFC (Kutcher et al) at Melfort, Sask., and Lacombe, Alta., in 2002-04, compared canola yields at row spacings of 23 cm (9”), 31 cm (12”) 46 cm (18”) and 61 cm (24”). The study included hybrid and OP varieties directed seeded into cereal stubble using a ConservaPak drill.  At all site-years, yield of the 23 cm (9”) row spacing treatment was greater than or equal to yields of other row spacings. Yield of the 23 cm row spacing was greater than all other row spacings at 2 site-years, Melfort 2002 and Melfort 2004. At Lacombe 2002, yields for 23 cm were similar to the 31 and 46 cm spacing, but greater than the 61 cm spacing. At Lacombe 2004, yields for 23 cm were similar to 31 cm spacing but greater than the 46 or 61 cm. At Melfort 2003 yields were similar across all treatments, except for reduced yields at 46 cm. There was no yield difference among row spacing treatments at Lacombe 2003.

    [9] Murray Hartman, oilseed specialist with Alberta Agriculture, meta-analysis.