BRANDON — It has been commonly held in most producer circles that soybeans are sensitive to seed-placed phosphorus, but that thinking might be wrong.
Soil scientist Don Flaten told farmers attending Manitoba Ag Days in Brandon a couple of weeks ago that even when soil phosphorus levels are very low, placing phosphorus with soybeans has little effect on yields.
Soybeans, like flax, are known nutrient scavengers. They use a lot of resources, but they want them in forms they find attractive at the time and will find ways to get them.
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Flaten said recent studies have shown that only when seed-row placed phosphorus reached 80 pounds to the acre, and on wider row spacings did the soybeans show diminished yields.
“No matter what we put on, we saw no response. Wide row spacing, sandy soils and high rates in dry conditions, nothing,” he said.
In fact the research showed that even soils that tested very low, below 10 parts per million using the Olsen phosphorus method, yields of up to 70 bushels were produced in Manitoba research.
“If I was a 60-year-old farmer thinking of retirement, or on rented land that I wasn’t worried about, or a spoiled brat kid farming Mom and Dad’s (land) I might not put on any (phosphorus),” he said about growing soybeans.
A good crop of soybeans will remove about 32 lb. of phosphorus from the soil. If the field is low in phosphorus to begin with, there is a risk that following crops such as cereals could be short of the nutrient.
Most other prairie crops need to start out with a test of about 15 p.p.m. Olsen phosphorus to reach an average or better than average yield.
The University of Manitoba re-searcher said many crops, besides soybeans, respond well to phosphorus applications in the year of application, up to recommended amounts.
michael.raine@producer.com
