Leanne Koroscil, On-Farm Network Agronomist, MPSG
Pulse Beat 96, Fall/Winter 2022
WHEN ASKED ABOUT his profession, my dad would often quip, “Professional gambler.” This is only partly true because he’s actually a farmer. But the seasonal complexities of farming enhance the importance of making economical and sustainable production decisions to ensure you’re playing your best hand.
One of the cards that can be played is seeding rate.
Small-plot research conducted at eight sites across Manitoba provided a general recommendation for soybean target plant stands of 140,000 to 160,000 live plants/ac. Note that target plant stand is not the same as seeding rate. Target plant stand is the ideal number of live plants/ac and accounts for factors that may affect seed survival rate:
Environmental
- Insects and plant pathogens can impact seed survivability.
- Cool temperatures may delay emergence.
- Soil crusting may inhibit emergence.
Handling
- Seed can be mechanically damaged at seeding depending on handling and equipment used.
- Results from our On-Farm Network (OFN) report an average of 80% survivability with a seeder and 82% survivability with a planter, though these rates may vary as not all equipment is alike.
Seed Lot Condition
- Condition of seed lots influences germination and survivability.
Soak or germination tests are simple tools to prepare you for your season: Soak 200 seeds in water and calculate the percentage of seeds that swell to determine seed coat damage. If a seed loses its seed coat, it will not produce a viable plant in the field. - Germination tests can be sent off for analysis at an accredited lab, or you can obtain one from your seed dealer,
or
- you can conduct your own test in-house by placing 100 seeds on a well-watered paper towel, then returning after a day or two to calculate the percentage of seeds with emerging radicles. Ensure the sample tested is a proper representation of your seed lot.
Plant stands can also be counted in-season at first trifoliate to calculate the percentage of seed survival. Future seeding rate decisions can be more informed by using the following calculation:
Once collected, these variables can easily be entered into the Soybean Seeding Rate Calculator on MPSG’s Bean App to calculate the appropriate seeding rate. Couple the rate from the app with knowledge from previous years and experience in your fields to start the season off on the right foot.
Every farm, piece of equipment, seed lot and season is different, which means there is no optimal seeding rate number represents the entirety of Manitoba. What is realistic however, is to consider seeding rate thoroughly, since a difference in seeding rate can mean major economic implications for your farm. To put seeding rates to the test and determine the most suitable rate for individual farms, seeding rate trials have been conducted through the OFN.
OFN SEEDING RATE TRIALS
Soybean seeding rates were the first (and now longest) running trial type in the OFN. As of 2022 there have been 107 soybean seeding rate trials conducted across agro-Manitoba, seven of which were established this year. The objective is straightforward: to quantify the agronomic and economic impacts of different seeding rates on soybean production.
Over the years, OFN trials have been conducted with several seeding rate combinations ranging from 100,000
to 252,000 seeds/ac. Seeding rates for trials are traditionally chosen based on the farmer’s typical seeding rate, plus or minus at least 30,000 seeds/ac between treatments. The OFN trials aim for this variation to ensure the treatments are different enough from each other and to analyze distinctions in agronomic and yield potential. The seven trials from the 2022 season specifically ranged between 110,000 to 226,000 seeds/ac. To further investigate seeding rate results, plant counts are collected twice after to determine if the plant population after seeding changed throughout the season. This is an important factor in data collection because of the effect plant population can have on soybeans throughout the season. More plants can increase competition between soybeans and can cause shade avoidance characteristics (thinner stems, taller plants). Higher plant populations can also create a thicker canopy which translates into less airflow, encouraging disease growth in a wetter year. Conversely, a thicker canopy can provide greater competition against weeds in the field.
To determine if any of these conditions may have affected the crop, plant counts are collected early and
late in the season and compiled. Higher seeding rates have been shown to have a lower survivability rate in OFN trials, especially by the reproductive (R) stages compared to lower seeding rates
(Table 1).
Finally, yield is calculated at harvest, taking into account economic considerations such as inputs and equipment costs. An economic yield increase implies that the seed costs were paid for by the increase in yield as a result of the trial treatments. The results are compiled into individualized reports and shared with the farmers.
2022 TRIAL UPDATE
The delayed start to the season brought with it a late harvest, and at the time
of this writing, all but one of the trials from the 2022 season were analyzed. Of the six trials analyzed, one had statistically significant differences between the seeding rate treatments of 166,000, 196,000 and 226,000 seeds/ac (Figure 1).
OFN research prior to 2022 saw 18 statistically significant responses only to yield, 12 of which also had economic yield increases. To be considered economic, the increase in yield must overpower the original seed costs (Table 2).
The 2022 Cost of Production Guidelines published by Manitoba Agriculture calculated soybeans to be $67.90/unit (1 unit = 140,000 seeds), thus a 30,000 seeds/ac difference can equate a cost difference of $14.55/ac. This is no small number, and underscores the importance of optimizing your seeding rate on your farm.
Figure 1. At the time of writing one seeding rate trial from the 2022 season showed significant differences between treatments.
WHAT’S NEXT
Continued interest in this trial type signals that seeding rate questions still exist for soybean farmers. Until that interest dwindles, the OFN will continue to grow the dataset.
Curious about which rate is ideal for your farm? Contribute to soybean seeding rate results with a trial by contacting Leanne Koroscil, OFN Agronomist, at leanne@manitobapulse.ca or 204-751-0439.