Canola yield losses caused by excess mono-ammonium phosphate placed next to seed can be tough to detect.
“It (seedling damage) can be really insidious…. It may be stealing bushels quietly without you being able to see it,” said Cynthia Grant, a soil fertility specialist at Agriculture Canada’s research centre in Brandon.
“Unless you have something side by side, where say you had a miss for fertilizer, you might not even notice it.
“Canola is sensitive to seed-placed phosphorus because the nitrogen that’s in the mono-ammonium phosphate can be damaging to the seed if you put too much on,” she said, noting the recommended limit for canola, on the Prairies, is 18 pounds per acre of phosphorus.
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Higher concentrations may damage the seed, but sufficient phosphorus is also crucial for the first few weeks of plant development. Given that conundrum, should canola growers use seed-placed MAP or not?
According to Grant, a grower must ensure that there’s enough phosphorus in the soil. Enhanced efficiency fertilizers might be the best way to protect the seedling.
“Enhanced efficiency fertilizers do seem to have an advantage in terms of reducing seedling damage,” said Grant. “It might allow you to adequately nourish your crop with phosphorus … without running the risk of seedling damage.”
Grant has completed the second year of a three-year trial, studying the potential benefits of placing slow-release MAP next to canola seed.
“We’re looking at the controlled released products from two viewpoints. Are they more efficient at lower rates? So can you get by with lower rates of application? ” Grant said.
“And secondly, are they less damaging at higher rates?”
Grant and other researchers have been applying polymer-coated MAP, standard MAP, liquid phosphorus and no phosphorus, on plots at two locations near Brandon, one with light soil and the other with heavier soil conditions.
They are gathering data on canola plant emergence, yield, oil content and other factors, but she isn’t ready to release the results. Unusual spring weather the last two years has affected the trials. She may have to extend the experiment to a fourth year to get reliable results.
Before this canola study, Grant conducted field trials where enhanced efficiency phosphorus was placed next to wheat seeds. Although the results have not been published, Grant said slow release phosphorus didn’t provide a yield boost.
“We really didn’t see a huge benefit…. Only in one year out of six did we see a distinct advantage to using the enhanced efficiency fertilizer.”
With the canola trials, Grant noted the enhanced products would likely be more beneficial, because canola is more sensitive to seed placed fertilizer than wheat.
She said seed placed MAP can damage canola seed in two ways: ammonia in the soil is directly toxic to the seedling and the fertilizer removes water from the seed.
“Fertilizers are all salts and the salt will basically suck the moisture out of the tissue of the germinating seedling and that causes osmotic damage,” she said.
That is why slow release fertilizer is useful. It meters out the amount of MAP adjacent to the seed but provides enough phosphorus for early growth.
Dale Tomasiewicz, manager of the Canada-Manitoba Crop Diversification Centre in Carberry, said sufficient phosphorus is essential to plant development in the early part of the year because the nutrient doesn’t flow easily through the soil.
“The other nutrients, to varying degrees, they come to the plant with the water, whereas the phosphorus has to move more directly from the soil to the root,” he said. “Phosphorus uptake from the soil is very dependent on an extensive root system, with a large root length in contact with the maximum amount of soil.”
Tomasiewicz added that plants are more likely to benefit from banded MAP when seeding is done early, because of slower root growth and slower diffusion rates when the soil is cold.
“Phosphorus fertilization may be slightly more important if you’re planting early, rather than late.”
