Much of a wheat crop’s yield potential is determined at seeding, so planting the right amount of seed to achieve the right target populations plays a huge role in the success of your crop.
Concerns like insect pressure, weed competition and fertility deficiencies can be managed throughout the growing season, but when it comes to seeding, you only have one chance to get it right. Much of a wheat crop’s yield potential is determined at seeding, so planting the right amount of seed to achieve the right target populations plays a huge role in the success of your crop.
Every wheat variety has its own recommended population at which it expresses its highest yield potential. For example, some varieties have a lower tillering count and good lodging scores so they respond better to higher populations. On the other hand, some varieties produce shorter heads when planted at high populations and are prone to lodging, so they perform best under lower populations.
This applies to both spring and winter wheat, although winter wheat varieties are generally seeded at lower population rates to help stimulate the plants to stool out, allowing for increased tillering before winter dormancy.
DETERMINING SEEDING RATES
Testing seed annually at a certified seed lab is an important step in establishing a good quality plant stand. Thousand kernel weight (TKW), germination, vigour and disease ratings and mortality are all factors to consider when calculating your seeding rate. Here’s a look at how each of those factors affect seeding rates:
Seeds per lb
While the exact seed size can change annually due to environmental factors, each individual wheat variety has a general seed size range. Varieties with larger seed size should be seeded at a higher lbs/acre seeding rate, while varieties with smaller seeds should have a lower lbs/acre seeding rate.
Calculating for germination rate is often overlooked. Your wheat supplier will provide the germination rate for your variety. One of several disadvantages to using bin-run seed is that you need to test for the germination rate on your own.
The average mortality rate is 10 percent for wheat seed, but it can vary on a field-by-field basis. The mortality rate may increase if you don’t use a seed treatment or if you seed into cold and/or dry soils. Seed vigor can have an impact on seed survivability as well. For example, with 92% germination and 88% vigor, we would expect 90% survivability. Trials on spring wheat indicate that pushing populations too high could drive the mortality rate up to 14 percent in some varieties, once again making it important to not exceed the recommended population rate for your wheat varieties.
If targeting a final stand of 28 plants/sq ft, begin by multiplying your desired plant stand (28) by your TKW. Then you will need to divide that number by your expected survivability (for this example, we’ll use an average of 90%). Take that number and divide by the constant 10.4 and you will have your final seed rate (lbs/ac). Round to the nearest pound.
- Variety A (larger seed size) has a TKW of 33.5g
- Variety B (smaller seed size) has a TKW of 23.5g
Variety A: 28 plants/sq.ft. x 33.5g TKW / Survivability (0.9 or 90%) / 10.4 = 100 lbs/ac total planting rate.
Variety B: 28 plants/sq.ft x 23.5g TKW / Survivability (0.9 or 90%) / 10.4 = 70 lbs/ac total planting rate.
ACCURATE STAND COUNTS HELP OPTIMIZE FUTURE YIELDS
Once your crop has established, it’s really important to take a live plant stand count to see if you were successful in achieving your target populations. Although it’s a common practice in row crops, this step often gets overlooked in wheat because it’s a busy time of year. Not hitting your target populations can result in lost profit potential, so you need to figure out went wrong so you can prevent it from happening again in the future.
A good practice is to ground-truth your acres when your crop has reached the 1- to 3-leaf stage. If you do it any later, tillers are often mistaken for main stems. Ask your local agronomist to join you so they can share insights on their observations and help with counting the stems. Using a 5-foot hoop will help provide a more accurate stand count than a 2½- or 3-foot hoop.
If you didn’t hit your target populations and you’re certain that your seeding rate calculations were correct, a mechanical mishap or environmental issue might have caused the problem. Asking yourself questions like these might help you determine what went wrong:
- Did I forget to use a seed treatment?
- Was the drill calibrated correctly?
- Did I drive too fast at seeding, causing inconsistent planting depth?
- Were soils compacted in the affected areas?
- Did I get good seed-to-soil contact?
- If planting into a no-till field, did hair pinning occur due to high residue?
Every field is different, so selecting the right varieties and planting them at the right seeding rates will go a long way in getting the most out of your wheat crop.