2004 Soybean Seed Quality Update

Soybean seed quality looks excellent for this spring. Over the last two years soybean seed quality has been lower because of dry growing conditions the previous year. Initial quality tests show above 90% germination in most lots of this years' seed. There are some exceptions in regions that were extremely dry or diseased. With very promising prices and lower winter wheat acres, soybean acreage will be up this year. Book your seed as soon as possible. Some of the "hottest" varieties are already sold out.

Small Seed Size

One of the most important seed issues for this year is seed size. In many cases, seed may be the smallest ever in Ontario. A dry August is part of the reason for small seed, but soybean aphids probably had the biggest role. In fields where a portion of the crop was sprayed with Matador for aphid control, the untreated plants yielded much smaller seed (80% of the size) than the treated plants.

Plant The Right Seeds Per Acre

Research suggests there are few problems with smaller seed. Quality, moisture, and disease incidence on the seed is what counts, not the actual size of the seed. The biggest advantage to small seed may be that we simply need fewer pounds per acre to achieve the same plant stand - significantly reducing seed costs. Planting the right number of seeds per acre will pay big dividends. Over-planting is not only a costly waste of seed but also increases the likelihood of lodging and white mould problems.

Table 1 shows the estimated number of seeds recommended at various row spacings. Remember that these rates are general recommendations and are designed to incorporate "tough conditions" such as early planting, no-till, heavy clay soil types, etc. Under ideal soil conditions, seeding rates can easily be reduced by 10%, since emergence will be greater.

When calculating your seeding rates, remember that germination and emergence are not the same thing. Compensate for the seed that does not emerge. Even under good conditions 5 to 15% of the seed may never develop to mature plants. If a stand density of 180 000 plants per acre is desired, plant 225 000 seeds per acre if the germination is 90% and the emergence is 90% (180 000 divided by 0.9 for germination and divided again by 0.9 for emergence).

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Seed Treatment

If using farm applied seed treatments it will be necessary to go with the high end of the application rate since most of the seed treatments are labeled as a certain amount of product per seed weight. Since the seed is smaller, each seed will get less coverage if you keep the rate the same. This is also true for innoculants.

Plant By Seeds Per Acre, Not By Lbs Per Acre

Consider the savings involved when using the proper seeding rate with small seed. This is illustrated in Table 2. Since soybean seed is generally small this year one bag of seed will go a lot further. This example assumes $36.00 per bag (22.7 kg, 50lbs) at 7500 seeds/kg (3400 seeds/lb).

*The estimated plant stand is based on 90% germination and 90% emergence.

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