According to a recently completed three-year study into the effects of lower seeding rates on soybean yields, growers must pay attention to both the cost of seed and individual plant survival rates when making seeding rate decisions.
This is one of the conclusions in a study by Ron Tone, Jordan Karpinchick and Elizabeth Karpinchick of Tone Ag Consulting, a St. Pierre Jolys, Man.-based independent agricultural consulting. The results of the study were included in a paper submitted to the Manitoba Agronomists’ Conference at the University of Manitoba in December, 2014.
The study, funded by the Manitoba Pulse Growers Association, took into account 26 on-farm population trials involving soybean growers in eastern Manitoba. Each trial included six strips planted with a higher seeding rate, alternating with six strips planted with a lower seeding rate. “The higher seeding rate represented the farmer’s normal seeding rate and we compared it with a reduced seeding rate of 30,000 seeds per acre less than their normal rate,” says Jordan Karpinchick.
For the 2014 trials, three air seeders and seven planters were used. Fields were on average half a mile long, and the strips varied in width between 40 and 80 feet, depending on the participating farmers’ ability to take a “pure” combine swath. Trials were scouted during each growing stage to monitor plant maturity and population, row closure and ground cover, and incidence of disease and insects, as well as rainfall. In all three years, soybean yields appeared to have little relationship with rainfall.
“Out of the 10 trials conducted in 2014, four of them showed an economic advantage for the high seeding rate at a soybean price of $10/bushel,” he says. “This shows that the most profitable seeding rate changes as the price of soybeans change.”
Data from the trial shows a 1.3 bushel/acre yield advantage to the fields seeded with a higher rate in 2014, but with the current prices at $10/bushel and the cost of 30,000 seeds at $13/acre, Karpinchick says there is no economic advantage for either the higher or the lower seeding rate averages in 2014.
“Looking at the plant populations we counted over the three-year study, the farmer needs to have between 120,000 to 140,000 plants per acre at first trifoliate and between 100,000 and 120,000 plants per acre at pre-harvest to achieve the maximum economic yield,” he explains. “When prices for soybeans start to drop, a reduction in seeding rates may be needed in order to maintain a profit.”
On the other hand, when prices rise above $11/bushel, the data from Karpinchick’s study illustrates that for planters, the higher seeding rate average of 173,000 seeds/acre was more profitable than the lower seeding rate average of 143,000 seeds/acre.
Case by case
Karpinchick says it’s up to growers to be aware both of the current survival rate of individual plants and of the price of seed in order to make informed seeding rate decisions for soybeans.
“It is important for growers to understand their input costs to determine their most profitable seeding rate based on the average seed mortality rates that we found in the three-year study,” he says.
Historically, Manitoba has seen a wide disparity in soybean seeding rates, and Manitoba agronomists and consultants have traditionally based their recommendations on Ontario and North Dakota guidelines. The study’s results offer Manitoba growers some much-needed data for making seeding decisions.
According to Karpinchick, the seed is the most expensive input for farmers growing Roundup-Ready soybeans, so determining the most economical seeding rate is an imperative.
He says that, based on the data collected for this study in eastern Manitoba, in conjunction with other soybean population research, the MPGA is working on building an app that will allow growers to input costs, plant population counts, and soybean price/bushel to help determine if they have achieved maximum profitability.
And data collection will continue. “We are currently working on a similar project in western Manitoba on determining optimal seeding rates and plant populations that will be concluded in 2017,” he says.
But seeding decisions should always be made on a case-by-case basis, regardless of the data.
“There are many factors such as germination, cracked seed, weed management, insects, pathogens, and seed varieties etc. that can affect seed survivability throughout the growing season,” Karpinchick says. “Thus, each grower has their own target seeding rate depending on these factors.”
Growers interested in participating in future field-scale trials are invited to contact Tone Ag Consulting.