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The Importance of Seeding by Thousand Kernel Weight (TKW)

For the past few weeks CropPro agronomists have been busy in the field with pre-seed and in-crop scouting as well as completing the first variable-rate assessment, focused on plant stand counts. It has been a challenging spring in many parts of the province due to a lack of spring soil moisture and rainfall over the last couple months and two noticeable challenges have arose from these tougher growing conditions: uneven emergence and lower than targeted plant stand counts.


It is very important to take the time during the winter to create a crop plan for successful plant stand establishment come spring. The fundamental building block to establishing a crop and having something to harvest in the fall is not just getting the seed into the ground but paying close attention to where that seed is being placed (i.e., into moisture or not and depth of seed placement) and the amount of seed going into the ground.


Planning for the amount of seed going into the ground starts with having your seed germ tested and thousand kernel weights (TKW) determined prior to seeding. These two seed characteristics along with mortality or survivability are used in an equation that determine your optimal seeding rate for targeting x number of plants per square foot (typically around 30 plants/ft2 in cereals and 7 plants/ ft2 in canola; these numbers may vary slightly depending on your location in the province but should roughly be targeting this). There can be drastic differences in seed lots based on seed size, therefore, seeding two different lots at the same seeding rate is not beneficial as the difference in size would correlate to different amounts of seed in the seed row.


There is a noticeable trend across fields that are seeded based on knowing germ and TKW and targeting plants/ft2 versus assuming your seed size or going with the normal average seeding rate that has always been used. The figure below illustrates the average plant stand counts from a field where the seeding rate was targeted just based on the average seeding rate that has been used throughout the years compared to a field from the same area where seeding rates were calculated in the winter based on knowing the germ and TKW and 30 plants/ft2 was then targeted in determining the seeding rate. The results were drastically different even though these same two fields are struggling with current lack of moisture conditions as well as soil surface crusting. When a suggested average seeding rate is used, the fields do not typically average close to the 30 plants/ft2 that we would normally be targeting for these cereal fields. Added onto this are the stresses from the spring (lack of moisture, soil crusting, etc.) that likely compounded the problem of not having enough plants in a square foot.


Figure 1. Average plant stand count on fields targeting average seeding rate alone vs. targeting seeding rate based on germ and TKW.



There are also many other benefits to targeting and hitting plant stand goals, especially when combined with variable rate seeding, which does not only improve yield; we also see more even emergence across the entire field (omitting the decreased plant stand counts on knolls and challenging depressions or saline areas) which then leads to easier timing of herbicide and fungicide applications. It can also create timelier and more even maturation in the fall which can lead to more efficient harvest and grain storage as well as avoiding fall frost damage.


Summary

This winter, once you have your seed in the bin, consider sending a sample away to an approved lab for a germ and TKW test. The seed does not have to be cleaned yet as the lab will clean the sample. This would be a best practice if you know your seed does not usually get cleaned until early spring and would not have the time to have the samples send away then. This is the first step in successfully establishing the next year’s crop and goes a long way in the planning process.



Chantal Bauche

Senior Precision Agronomist

chantal@swatmaps.com

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