Seed Depth Assessment

Seeding too deep is a common stand establishment issue in canola. This becomes clear as plants emerge, especially when some rows emerge earlier and more vigorously than others. Recently emerged plants provide an easy way to assess the drill for seed depth accuracy. To find out what percentage of plants were seeded at the target depth, simply dig up plants from a few different rows and measure the white part of the stem. (Note: If any part of the stem above-ground has remained white, you can measure this before pulling it out.)

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Use a seed depth tool to mark the depth where seed was found.

If some rows or sections are worse than others, check the drill to see what might be the cause and how that can be fixed for next year.

 

Are all the rows emerging at the same time?

If not, this is the first indication that there were some incorrect adjustments on the seeder. This observation is best made just as the final plants are emerging. In another week if the plants in the adjacent rows have grown to close to the same stage, the slight variation won’t be a problem. But fine tuning the seeder will ensure uniform maturity.

Front rows late

Caused by soil stacking as a result of the adjacent openers throwing soil into the front furrows increasing the depth of soil. The front of the seeder could be set too deep.

Rear rows late

The opener wasn’t deep enough to produce sufficient soil cover over the seed leaving the seed in dry soil or even uncovered.

Occasional rows late

The shank and opener that planted that row is not adjusted properly and is penetrating too deep. May also be an opener following in a wheel track and not penetrating to moisture, or the soil is working up too lumpy to pack properly.

Plants are missing within a row

  • Long gaps (6 inches or more) are likely the result of seed being retarded in the seed delivery line or in the seed delivery boot.
  • Small gaps often result from insufficient packing due to lumps in the seed bed. It is often difficult to prevent this in clay soils. Unless rain occurs soon after seeding, these missing plants will not likely show up later to interfere with the harvesting. Yields may not be affected by small gaps in the seed row.
  • Irregular gaps are most likely the result of poor seed to soil contact and can result from seeding too shallow. These missing plants may show up later after a significant rainfall.

Plants missing under lumps of soil and residue

Residue conditions often cause straw and eventually soil to drag with the opener. At some point the pile of material rolls off and either falls back on the seed row or onto the adjacent row. Sometimes plants will emerge through the pile but will be later in maturity.

By length of row. Use a metre stick and count the seedlings per metre of row. Take that number and multiply by 100 then divide by the seed row spacing in cm to get plants per square metre. For example, 25 plants per metre multiplied by 100 then divided by 25 cm (10” row spacing) is 100 plants per square metre. (Divide by 10 if you want plants per square foot.) Repeat.

Using hoops: To do counts, use a hoop with an inside diameter of 56 cm. This is equivalent to 0.25 of a square metre. Count the number of plants inside the hoop, and multiply by 4 to get plants per square metre. (Divide by 10 if you want plants per square foot.) Repeat.

If plant counts are lower than you expected based on your seeding rate, taking time now to figure out why will help fix the problem for next year. Use the Canola Diagnostic Tool to help. While scouting, look for the following, which will help with the diagnosis:

Differences row by row. Are some rows good and others thin? Or does it seems like strips of rows are poor while the rest are OK? These are likely the result of drill malfunction, or seeding too fast, with rear openers burying the front rows too deep. Openers may be worn or broken and no longer providing adequate isolation from fertilizer band. Check for seed depth and placement. Identifying these issues now will help to improve drill performance for next year.

Low emergence overall. If low emergence is fairly general throughout the field, seed may have been placed too deep, excessive fertilizer may have been placed near the seed, seeding rate may have been too low or seed quality was compromised. Large seed size combined with lower seeding rate and low seedling survival can result in thin stands. Consider this for next year.

Uneven growth staging. Large plants interspersed with late-emerging small plants can result from inconsistent seed depth from seed to seed. High fan speed on the drill may have caused seed bounce, which results in inconsistent seed placement. Worn openers and uneven residue cover are other possible factors.

Bald patches. Blank areas in the field can result from dry seedbeds, heavy winds, drowned plants, seed rots, cutworms and other insects, and from gophers.

Unthrifty, yellow or malformed plants. Unhealthy-looking plants can result from seedling diseases, herbicide carryover, herbicide burn, high rates of seed-placed fertilizer, fertilizer deficiency, low vigor and deep seeding, to name a few. Malformed plants can result from herbicide injury or disease, but possibly other factors.

Damaged plants. Environmental stress such as frost or hail are possible reasons. Look for insects, particularly flea beetles and cutworms, but also wireworms and early grasshoppers. Even if you don’t see obvious feeding on leaves, look under the leaves and on stems. If flea beetles have moved down the plant due to rain or wind, they can actually do more damage. Severing a stem is far worse than 25% damage on the leaf. Check leaves for blackleg lesions.

While doing the above ground scan, look at the weeds. What type, size and number do you see? This will help determine whether another spray is warranted and what tank mix and rate to use.

After the above-ground assessment, get a trowel and bucket and start digging around damaged plants. Look for cutworms and wireworms in the top 4” of soil. Look at the roots for signs of insect feeding or disease damage. Chomped roots are usually insect damage. Mushy or thin wiry roots and stems are often the result of seedling disease.

Thin stands need extra protection

The key with a thin stand is to do what it takes to protect those plants. A stand needs a minimum of 4-5 plants per square foot to reach its yield potential. For a canola field at or below that plant population, consider lowering the action thresholds for insect, weed and disease management all season long.

It helps to keep a scouting notebook and jot down all observations. Even if you see nothing of concern, early scouting gives you a baseline for crop emergence and condition of the stand. Then you’ll know for sure something is wrong if the crop doesn’t look as healthy the next time you scout.

Problems can escalate quickly this time of year and cause irreparable damage if not addressed early. Scouting alerts you to these problems. And while the cause and solution may not always be obvious, this insight motivates you to get help and make an informed decision on the most economic course of action.

Acknowledgements

http://www.canolawatch.org/2016/06/15/seed-depth-assessment/