When in doubt, dig deeper

Expert says nutrients can vary within small areas and across fields, so take samples in spring and use multiple soil samples for best results. | File illustration

WATROUS, Sask. — Sometimes farmers need to dig a little deeper, says a University of Saskatchewan soil scientist.

A six-inch soil test will give farmers a good read on things like phosphorus and potassium, but other micronutrients are more mobile.

“I think it’s always, especially under wet conditions, a good idea to occasionally check below the top foot,” he said.

“In other words, go down to the 12 to 24 inch depth occasionally and check for that deep nitrate and deep sulfate,” Jeff Schoenau told an agronomy workshop in Watrous last week, noting many growers soil test at zero to 12 inches as a compromise.

“You want to be able to account for that. It (the nutrients) may not be available to your crop right away, but once the water starts to move to where the roots are, it’s going to carry some of that … with it.”

He said farmers can get accurate soil tests in the fall when soil begins to cool, but when there’s a large runoff or leeching, producers can benefit from a spring sample.

Soil tests will benefit producers who had water issues the previous year, he added.

Schoenau said growers can expect to see lower nitrogen levels in fields that were too wet to seed and that remained waterlogged throughout the 2014 season. He said more nitrogen will become available because of mineralization if those areas dry up this year.

“If you have a field that part of it didn’t end up getting seeded, or a whole field or even these small areas within that field, they’re candidates certainly for changing the rate of fertilizer to be added,” said Schoenau, who recommended sampling and managing these areas separately.

“Adjusted fertilizer rates can pay off in those areas with better fertilizer efficiency and subsequently improved return on the dollar.”

Schoenau said nutrients vary dramatically both in small areas and across fields, citing residual fertilizer bands in no-till systems as a factor. This means multiple samples are needed to create a composite that is a “reasonable representation.”

He said producers should take at least 10 to 15 samples on an 80 acre field.

“There’s no way that you can go out into a field and take two or three cores out of that field and anticipate it to be very representative of that field,” he said.

“It’s going to take a few more than that.”

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