With the introduction of airseeders using independently linked openers, a lot of attention has been focused recently on the accuracy of seed and fertilizer placement. But that is only half the story when it comes to precision seeding. Metering out the right volume of seed to establish the correct plant population is the other part of the equation.
Guesswork and rules of thumb aren’t good enough anymore when calculating seeding rates. “There is homework you have to do,” says Ken Panchuk, a provincial soils specialist with Saskatchewan Ministry of Agriculture. And that starts with knowing the 1,000-kernel weight of the seed, which is the starting point for establishing precise settings on modern seeding equipment.
Metering systems on implements used for seeding small grains are designed to dispense seed based on weight, so knowing how many kernels there are in a given weight is important, particularly when targeting a specific plant population.
Seed growers usually provide 1,000-kernel weights when selling pedigreed seed. But Venkata Vakulabharanam, provincial oilseeds specialist, also with Saskatchewan Ministry of Agriculture, recommends verifying that data yourself. “Kernel weights can vary between seed lots,” he says. The more accurate information you have, the easier it will be to establish a crop with the correct plant density. Fields with uneven establishment or incorrect plant densities can see yield reductions of up to 20 per cent, Vakulabharanam says.
Targeting the ideal number of plants per square foot is the objective. “There is a range of plant stands that will give similar yields,” says Panchuk. “You want to be able to seed at the lowest rate to minimize your cost per acre.” Seeding rates that are too high waste resources and can
“There is a range of plant stands that will give similar yields. You want to be able to seed at the lowest rate to minimize your cost per acre.”
— KEN PANCHUK
actually be counterproductive. In drier soil zones, having too many plants per square foot will create very high competition for limited soil moisture, lowering overall yields.
Even under the best conditions, yield levels eventually plateau. Seeding to achieve plant stands above the recommended population wastes resources with no economic return. If the rate is too low, the crop canopy develops too slowly and weeds become a bigger problem. You have some strong economic benefits to getting things right. But the more closely a producer tries to come to the ideal plant density, the less margin there is for error.
ESTIMATE SEEDLING MORTALITY
Once the 1,000-kernel weight is known, the next step is to figure out how many plants will emerge from every 100 seeds planted. A germination test determines what percentage of seeds is viable, but that still doesn’t provide enough data. Having a lab also perform a vigour test for canola or a stress test for cereals will provide a better picture of how many seeds will actually produce plants.
Vakulabharanam says the average survival rate for seeded canola is around 50 per cent. But that can vary from as low as 30 to as high as 80 per cent with varying management practices and environmental conditions. The ideal plant population for canola is seven to 14 plants per square foot.
To fine tune your seeding rate for your specific data and targets, this is the equation to use, according the Alberta Ag Tech Centre: Seeding rate (lb./ac.) = desired plant population/ft x 1,000-kernel weight (grams) seedling survival rate (in decimal form such as 0.90) 10.4. This formula works for both oilseeds and cereals.
Just to make things even more complicated, producers need to take weather conditions into account. Panchuk says seed that stays in the ground for longer periods before germinating, due to cold spring conditions, can suffer higher-than-expected mortality rates. In years when spring conditions are less than ideal, producers should lower the calculated survival rate when using the plant density equation.
And Vakulabharanam notes that seeds placed too close to fertilizer will also suffer, which means the placement accuracy of any seeder also comes into play. Along with that, very high fan speeds can cause damage to seeds, and travelling too fast can cause implements to bounce, placing some seeds too deep.
All of this means producers need to rely in part on their experience and knowledge when it comes to their fields and equipment. That makes it even more critical to scout fields each year and see exactly how crops emerge, making notes that include data on plant density, emergence and seeding practices. Knowing all the factors is essential for fine tuning seeding procedures.
As precision becomes the buzzword in agriculture, Panchuk notes that many large-seeded crops, such as corn and soybeans, are now sold in containers that actually list the number of seeds inside. As growers of small grains increasingly take note of the importance of exact seeding rates, will we see that trend carry over? Or will we at least see cereals and oilseeds being sold in smaller lots identified by much more specific seed data?
Scott Garvey specializes in writing about tractors and farm machinery technology for publications in Canada and Great Britain. He’s also a former affiliate member of the Society of Automotive Engineers (SAE). He farms near Moosomin, Sask.