For years, germination/vigour has been the standard by which seed quality has been measured. The longer I’m in this business, the more convinced I become that thousand kernel weight (TKW), when combined with the germination or vigour result, is actually the standard by which seed quality should be measured.

Why? Farm inputs — particularly seed and fuel costs — are increasing. This is where seed count — or TKW — becomes crucial. TKW is the weight, in grams, of 1,000 seeds from a seed sample. It is used for calculating optimal seeding rates for the variety and growing conditions.

A TKW number is generated so the farmer can calibrate the seed drill to plant a known number of seeds per acre. If you know what your seed count is relative to the germination/vigour of your seed, that seed will go further, you will save money by only seeding what is necessary and you’ll get a more even emergence. This is crucial as we move into the age of climate change.

The seed testing industry has always used the standard germination as a benchmark. This is the fundamental step in assessing the planting potential of your crop. It is however the TKW that is the most practical tool for farmers to use in calculating their optimal seeding rate.

In order to calculate the optimal seeding rate for your crop, you’ll need:

  • The TKW of your seed lot;
  • The germination percentage of your seed lot;
  • The desired plant population (DPP) for that crop; and
  • The estimated seedling survival rate — subtract 5% to 20% (cereals) from the germination rate. Typically the higher the germination and vigour result, the stronger the field emergence.

As a rule of thumb, seedling survival rates in cereals are typically 80% to 90% but can drop significantly under adverse growing conditions. If growing conditions are good, subtract 5% to 10% from the germination rate to get a reasonable estimate of seedling survival. If conditions are poor, subtract a higher percentage. In the end, it is an estimate, but the better and more honest the estimate, the more accurate the seeding rate will be. When calculating seeding rate, express the seedling survival rate in decimal form (90% is expressed as 0.90).

TKW calculations have been available for many years, but unfortunately have been underrated. It is only most recently that bagged seed has the seeding rate on the label. In other parts of the world seed is now being sold as an acre package. TKW is becoming more important in this age of automation. A tool like this can actually tell a grower far more about seed quality when using the germination and vigour number in conjunction with the seed weight.

It is my opinion that in the future the TKW will be recognized as one of the most valuable tools for seed users. Targeting the desired plant population for an expected successful outcome makes the most sense economically and practically, especially since there are demands on the agricultural industry to produce more with less.

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