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How much fertilizer do you need to apply?

Agronomy research scientist offers his tips for planning your applications this spring

Soil testing will give you a plan for getting the biggest bang for your fertilizer buck, says provincial research scientist Doon Pauly. 
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Soil tests are still the best way to determine your fertilizer requirements for spring.

“We can determine where we’re starting from as far as the nitrate that is present in the soil and what’s there for the plant at the start of the year,” said agronomy research scientist Doon Pauly.

“Phosphorus, potassium, and salinity don’t change much year to year. However, the tests show you trends over time that give clues about your fertilizer management. If your phosphorus is gradually improving, that is a sign you’re doing a pretty good job of matching at least what you are taking off the land.”

For nitrogen, it’s important to consider the amount of loss.

“Your loss potential over winter is fairly low if you are in an area where you don’t typically have saturated conditions in the spring,” said Pauly. “If your normal practice in the spring is banding ahead of time, your loss potential is relatively low. We seldom have the conditions in a lot of the province where we have saturated soils after a spring fertilization event. We are not at a high risk for nitrogen losses every year.”

There is not a lot of loss difference between a two-pass and a one-pass system.

“The one-pass system should be comparable as long as the soil is sealing behind your application equipment, and it is giving you the seed soil separation that it is designed to,” said Pauly. “If you don’t want to handle a huge amount of dry fertilizer during the seeding operation, you can design a system where you are surface applying a little bit of nitrogen or a portion of that nitrogen early in the growing season and have it work very well.

“As long as the nitrogen is in the root zone by mid-June in most of the province, you can do a lot of different application strategies.”

Placing phosphorus depends on what has been previously done to the land.

“You will tend to see a larger effect from seed-placed phosphorus if your land is more deficient or if your phosphorus use has been less that what you have been pulling off in crops,” said Pauly. “You can get away with having phosphorus a little farther away from the seed if your soil tests higher, or if you have been applying a reasonable amount of phosphorus over time.”

The soil test for potassium is fairly reliable.

“If you are above 300 pounds of potassium based on (a) zero- to six-inch sample, the chances of you seeing a benefit from fertilizing with potash are pretty slim. But if you are below 200 pounds, then the chances of you seeing a response to your potassium on your cereal crops is actually pretty good.”

Gauging sulphur levels in soil test samples can be difficult to determine as it is mobile and can accumulate in so-called hot spots.

“That’s why typically I suspect most producers who are growing canola are putting down about 15 pounds of sulphur per acre regardless what is found in the soil test,” said Pauly.

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