Broadcast seeding canola – Tips

May 17, 2017 - Issue 8

Consistent success for canola crop establishment tends to come when seed is placed 1/2” to 1” deep into warm, moist soil and packed lightly for rapid and uniform emergence. Broadcast seeding is often considered a last resort, only to be used when proper placement with a drill is not possible.

In late springs with wet conditions, broadcast seeding may be the only way to get the job done. In fact, broadcasting may actually provide better seed placement than “mudding in” seed with a drill. Broadcast seeding now could also have higher yield potential than waiting two weeks for the ground to support the drill.

This canola was broadcast onto fairly heavy residue. Source: Justine Cornelsen

This canola was broadcast onto fairly heavy residue. Source: Justine Cornelsen

The same field was then harrowed, which will improve seed to soil contact. Source: Justine Cornelsen

The same field was then harrowed, which will improve seed to soil contact. Source: Justine Cornelsen

When broadcast seeding, it may help to:

Increase the seeding rate. Seed germination and seedling survival for broadcast canola could be lower compared to seed drilled into a moist, packed seedbed. However, broadcast seeding does not always mean low seed survival. For example, in the Canola Council of Canada’s Ultimate Canola Challenge site in Manitoba in 2013, canola broadcast onto moist warm soil had exceptional seed survival. To be on the safe side, consider an increase of 1 lb./ac. compared to what you would seed with the drill to compensate for lower seed survival expectations.

Adjust fertility practices. The same conditions that delay seeding with the drill (soft fields) can also force an adjustment to fertilizer rates and application methods. Fertilizer considerations for broadcast-seeded fields include:
—Adjust the phosphorus rate. Because broadcasting does not allow for in-row placement of seed and phosphate, doubling the phosphorus rate when broadcasting will improve the average proximity of seed and fertilizer prills on the soil surface. This could help emergence under low soil P levels, especially if soils are cool. However, if baseline soil P levels are medium to high and soils are warm and moist, fields may provide enough P to get the crop through the season. Growers could then apply a replacement rate in the fall or following years.
—Account for higher nitrogen losses. Broadcast nitrogen has a higher risk of denitrification when applied on saturated soils, reducing N fertilizer efficiency. Increasing the nitrogen rate by 20% to compensate for losses could be a strategy. Controlled-release nitrogen or N-loss inhibitors will help reduce these losses. These products increase the cost of nitrogen but they may be worth the extra cost when applying fertilizer in less than ideal conditions. Keep in mind a realistic target yield based on the time of year and field conditions, then set nitrogen rates accordingly.

—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, if needed. 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. Controlled-release or safener products would reduce losses from unincorporated fertilizer.

Assess residue risk. Successful broadcast seeding requires good seed to soil contact. This may not be possible in fields with lots of straw cover. With a thick layer of thatch, seed and fertilizer are not getting down to the soil surface. Spring cultivating ahead of broadcasting could create an equally inhospitable seedbed, with large clods and a crusted soil surface. Fields with thick residue that are too wet for a cultivator or harrows probably shouldn’t be broadcast seeded. Seed can germinate in residue, but it is not anchored, so can dry up and blow away in the wind.

Cultivate or harrow after seeding. This is an important step in broadcast success. Shallow cultivation or harrowing (if cultivation is impossible due to wet conditions) will help improve seed to soil contact, and greatly improve results. Light cultivation followed by one or two harrow-pack passes can work well. Avoid creating lumps or clods during cultivation or straw piles with harrows or cultivators. And take care with tillage depth. Seed with enough moisture to emerge on the surface or harrowed slightly below the surface will have relatively uniform emergence. Heavier or repeated tillage increases seed depth variability, which can lead to lower seed survival, a wider range of emergence dates and possibly lower yields. If a field was cultivated before broadcasting, a harrow pass may be needed to firm it up otherwise seed could end up at variable depths.

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 can tolerate glyphosate at any time, including on the seed.

Reset expectations. Yield for broadcast seeded canola is usually lower than yield for canola seeded evenly and properly with a drill, particularly if rain doesn’t happen shortly after incorporation. Growers should also prepare for increased management throughout the entire season, including weed control, fungicide timing and harvest timing decisions.

Consider wind effect on distribution pattern. A boom-based spreader with the boom fairly close to the ground may not have much of a problem spreading seed and fertilizer in the wind. While some will blow somewhat off course, the field should still be fairly evenly blanketed. The bigger risk would be for spinner spreaders where all seed and fertilizer is coming from one spot and the spread target is much wider. In this situation, application would be better on relatively calm days.

Further reading:

Broadcast seeding by air is even more risky.

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