Fertilizer experts say a serious phosphorus deficiency is developing in western Canadian soil.
Rigas Karamanos, senior agronomist with Koch Agronomic Services, has tracked the amount of phosphorus removed from and applied to soil since 2002.
There are only two dry years, 2003 and 2004, where farmers applied more than they removed.
The remainder of those years there has been a deficiency, and in some of those years the deficiency was substantial, such as 2008 when it amounted to 400,000 tonnes.
That’s because every bushel of canola removes .9 pounds of the nutrient from an acre of soil, which means a 60 bushel canola crop removes 54 lb. of phosphorus per acre.
“Who is applying 54 lb.?” he asked delegates attending the 2016 Saskatchewan canoLab workshop in Saskatoon.
Even if they are, phosphorus use efficiency in a canola crop is 30 percent in the first year of application.
Karamanos said the good news is that phosphorus soil tests are the most accurate of all soil tests with a margin of error of plus or minus .8 lb. per acre.
There is a 100 percent probability of getting a yield response from applying phosphorus if the test shows less than five parts per million, or 10 pounds per acre, of the ingredient in the top six inches of the soil,.
Anything in the five to 10 p.p.m. range has a 75 percent chance, 10 to 20 p.p.m. has a 50 percent probability and more than 20 p.p.m. has a 25 percent chance.
Thom Weir, senior agronomist with Farmers Edge, encouraged growers to keep an accounting table of how much phosphorus is applied and removed on each field every year.
Many farmers don’t apply fertilizer to their pulse crops.
“You go in the hole big time with a 60 bu. pea crop,” he said.
He encouraged growers to apply 50 to 55 lb. of phosphorus per acre with their cereal crops to make up for the years when they are growing canola and pulses.
Edgar Hammermeister, Western Ag’s manager of professional agronomy for southeastern Saskatchewan and Manitoba, said soybeans are another big “exporter” of phosphorus.
“Even though the soybeans won’t respond to the phosphate fertilizer, to protect your future crop yields you need to be using phosphate,” he said.
Hammermeister said new information is also available on how much nitrogen growers need to apply to their canola crops.
Conventional wisdom says farmers should apply three to 3.5 lb. of nitrogen per acre for every bushel of yield.
However, that research was conducted following decades of tilling the soil. Many farms have been no-till for 10 to 25 years.
“Now the soil has gotten into more of a balance, and there is more of a mineral potential,” he said.
Hammermeister said the new recommendation is for two lb. of nitrogen per bushel of yield.
Weir said farmers should not top dress their crops with nitrogen because they would need to do it at the same busy time of the year when they are applying fungicide, herbicide and insecticide.
As well, it could be raining or wet, which makes foliar application a high-risk strategy.
“I’ve seen a lot more wrecks by trying to do it that way than success,” he said.
Farmers may not get the best yields by applying all their nitrogen in the fall or spring, but 95 percent of the time it is the best strategy.
Weir also advised canola growers against applying potassium to their fields. The only time that needs to be done is when potassium levels in the soil are below 125 p.p.m., which is rare in Western Canada.
Hammermeister said canola’s superior root system allows it to extract 1.5 to 1.8 times as much potassium from the soil as a wheat crop.