Update from the On-Farm Network
Megan Bourns, MSc, Agronomist – On-Farm Network, MPSG – Spring 2021 Pulse Beat
Yield development is not a simple, predictable process, regardless of what yield-contributing factor you consider. This holds true for optimizing seeding rate, which initializes the range of potential yield. We can only have successful yield if we have successful seed in place to grow that yield.
What are the steps to determine how much seed we need to achieve our target yield? What management and environmental factors affect the success of our seed? And ultimately, what do we do with this information?
Yield Response Update – 2020 Results
In 2020, the On-Farm Network (OFN) completed another 11 seeding rate trials, two of which had significant yield differences between treatments. Adding the 2020 trials to the overall dataset, the frequency of soybean response to seeding rate remains at 21% (Figure 1). Out of 86 total trials, 18 have had a significant difference in yield between seeding rates, with varying economic outcomes (Table 1).
Seed to yield — a different story in different places
Soybean seed is expensive, there are no two ways about it. Based on current soybean seed prices, reducing seeding rate by 30,000 seeds/ac, for example, results in savings of $14.25/ac. What are the steps to define an optimal seeding rate? Before we launch in, I think it is important to set a foundation of individualization — the optimal seeding rate for one farm in one area of Manitoba, in one growing season, may not be the same as the optimal rate for another farm in another area or perhaps another season. Seeding rate sets the foundation for yield, but the outcome of that seeding rate is very farm- and field-specific. We see this variation in yield outcomes at the same seeding rates across trials in the OFN. For example, at seeding rates of 130k, 160k and 190k, yield has varied as much as 45 bu/ac across sites and years (Figure 2).
Set a target, determine seeding rate
Seeding rate decisions begin with determining target plant stand. This is the number of live plants/ac that you want to establish. The general recommendation for soybean target plant stand in Manitoba is 140k to 160k live plants/ac. Your target plant stand may be outside of this range, based on your production conditions and past knowledge about stand performance in terms of yield for your specific fields — and that is okay. The point is to target a plant stand that will generate desired yield as successfully and reliably as possible.
How do you translate target plant stand into seeding rate? We know that not every seed in the furrow will develop into a yield-producing plant, so our seeding rate should be greater than our target plant stand to account for expected loss. What influences seed survivability?
Seed lot and seed quality
Different seed lots and quality will change expected survivability. Germination tests and soak tests are useful tools to assess the expected survivability based on the quality of your seed lot.
Seeding equipment
The general expectation is 70–75% seed survivability using an air seeder and 80–85% survivability using a planter. However, this can vary greatly with equipment and seed handling. Among the 86 OFN seeding rate trials, survivability has averaged 80% for air seeders and 83% for planters. The best course of action to determine survivability for your equipment is to do your own early-season plant counts and survivability calculations.
Seedbed
A combination of soil conditions at seeding will affect survivability. Too dry, too wet, caking, pulverization that can leading to extensive blowing after seeding — all of these factors can influence seed survivability. Seeding conditions, particularly soil moisture, also play into seed depth decisions, which can affect emergence and survivability.
Insect and disease pressure
Wireworms, seed corn maggot, cutworms and seedling root rots, if present, can all impact plant stand.
Weather
Although out of your control and hard to predict, temperature, precipitation and wind can influence survivability in some years.
The goal is to determine the percentage you should increase your seeding rate over and above your target plant stand to account for all the factors contributing to lack of survivability. Obviously, this is easier for some survivability factors than others. Luckily, MPSG has a handy tool to aid in this calculation — the Bean App.
Count your plants!
A critical step in evaluating seeding rate performance is getting out to scout. Target stand is what you want, seeding rate is what you put in the ground and actual plant stand is what grows. While counting plants may seem like a bit of a pain, the information is very valuable in assessing performance of a seeding rate.
There are multiple methods for plant counting to determine stand, but they all involve counting the number of plants in a given area and then multiplying that by the necessary factor to convert it to plants/ac. MPSG’s handy Bean App has a built-in plant stand calculator to make this as simple as possible for you in the field.
Survivability, or % emergence, is calculated by taking the live plants/ac, dividing by your seeding rate (seeds/ ac) and multiplying by 100%. Compare this to your expected survivability and target plant stand to determine how your seeding rate performed.
Plant stand and survivability are useful tools to understand your yield at the end of the season — if you seeded at 180,000 seeds/ac with an expected survivability of 80%, but you only ended up with 60% survivability, yield could be limited by a low plant stand.
Was it really dry in the spring? Were you seeding into moisture? Did you observe insect damage in the seedlings? How did growing season conditions compare to other years? Doing some detective work to determine, as best as possible, what factors contributed to actual plant stand, can help adjust seeding rate for those circumstances in future years.
If a change in seeding rate is something you are considering for your farm, and you would like to assess how various options perform in your fields, the OFN is happy to help!
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