Seeding too fast can cause a number of problems that impact emergence resulting in reduced crop yield and/or crop quality.
The common speed range for most direct seeders is somewhere between 4.5 and 5.5 mph, but the speed at which any field can be seeded will depend on a number of interactive factors. These include soil type, soil moisture, opener design, soil flow around the opener, the crop to be seeded, and the previous crop residue – to name just a few.
One of the major detrimental effects of seeding too fast is uneven seeding depth. As seeding speed increases, soil displacement by the opener changes. Accurate direct seeding at shallow depth requires an even flow of soil around the opener for good seed to soil contact. Furrow closure, packing, and field finish can all be adversely affected by high speed.
Doug Moisey with the Canola Council of Canada measured seed placement of canola under good seeding conditions with a simple single-shoot opener. The chart below shows that as ground speed increased, so did the average depth of seeding. The range of placement also changed significantly.
The negative effects from increasing seeding speed are likely to be even worse with larger double-shoot openers where the problem can be further compounded as soil from one opener is thrown over the adjacent row resulting in more soil packed over the seed, effectively increasing the depth of the planted seed.
With air seeders, further trouble may occur when the fan speed is increased in order to deliver the required seed and fertilizer without plugging at a higher ground speed. Increasing air velocity has been shown to reduce seed germination under certain conditions, and often results in seed bounce. Excessive seed bounce impacts precision placement.
The effect of seeding speed on emergence and placement of canola using a single shoot opener
Uneven seed placement created by seeding too fast will cause problems that can affect the crop from germination to harvest, including:
Deep seed is placed in cooler soil, is slower to emerge, is more vulnerable to early season disease, and uses more energy reserve just to get out of the ground.
Uneven germination extends the window of vulnerability to pests like flea beetles – making it harder for the crop to quickly out grow the problem.
Timely weed control becomes more difficult when herbicide spraying is forced to be delayed in order to allow the entire crop to enter the safe staging for application.
Maturity of the crop may also be uneven, making the timing of pre-harvest applications and swathing more difficult, while lowering grades and reducing yields.
The only way to determine the correct seeding speed and depth is to get off the tractor and physically check where the seed ends up.
Is it in the row and at a consistent and desired depth?
Check several adjacent rows across the width of the seeder. Check rows that may be affected by wheel tracks from the tractor, the drill, or the air cart.
Check several areas of the field – soil conditions in headlands, low spots and knolls will likely be different – sometimes adjusting speed for specific areas will produce more consistent depth results
Increasing seeding speed also requires you to increase the fan speed in order to move the required product to the openers. This can result in seed bashing, which can split the seeds reducing germination or damage the seed in a way that makes it more susceptible to disease.
While the need to get the crop planted in a timely manner is critical, it is also important for direct seeders to consider the serious consequences of speeding up to seed more acres faster. That extra half-mile an hour may be costing more than realized. For many experienced growers, direct seeding a diversified crop rotation to spread out the seasonal workload has provided many agronomic benefits in addition to a wider seeding window.
A farmer can learn a great deal from a very simple seeding-speed trial on his own farm with his own equipment.
chart & pictures coutesy of Doug Moisey, Canola Council of Canada