Soil testing even more crucial after drought year

A poor crop year means nutrients may be left in the soil. An accurate reading of what’s there can help farmers reduce costs and manage nutrients better

The humble soil test is your best bet this fall for better nutrient management after a drought.

After a drought year, soil testing is more crucial than ever — and farmers may like the results they get.

“In the driest areas with the poorest yields, we’re hearing of very high levels of nitrogen remaining,” said John Heard, soil fertility specialist with Manitoba Agriculture and Resource Development.

Xiaopeng Gao. photo: Supplied

“I have never been so curious about soil testing as this year,” said Xiaopeng Gao, assistant professor of soil science at the University of Manitoba.

Both soils specialists said the hot, dry summer will likely have effects on what nutrients are left in the soil. Where drought reduced crop yields, a lot of applied nitrogen may still be present and intact in the soil.

Because the plants produced less biomass and less yield, they pulled fewer nutrients from the soil, said Gao. Dry conditions likely meant less N was lost to leaching and denitrification. Meanwhile, warm conditions may have increased mineralization from organic matter in the soil.

Heard said he spoke to someone whose test turned up 220 lbs. per acre residual nitrogen on a field where canola wasn’t harvested — this compares to an expected range of 20 to 40 lbs. residual N in a normal year.

In August, some areas received a higher rainfall than average said Gao. This means that residual N may have leached deeper into the soil.

Gao warned farmers to test for N to two feet (61 cm) depth to ensure a more accurate result.

Producers may find unused phosphorus in their soil as well. However, this phosphorus will have reacted with the soil and, while banked in reserve, may not be immediately available.

Testing can reveal if the soil is at a good working range, and if it is, farmers may be able to skimp on P application next year, said Heard. This will depend on if they hope to grow a P-sensitive or efficient crop, Gao added.

John Heard. photo: Supplied

“(It is a) short-term approach that will deplete soil reserves but may tide them over a year of high fertilizer prices,” Heard said.

However, he cautioned that farmers should not reduce fertilizer application on a gut feeling.

“With the soil test that then arms you with information by which to reduce next year’s applications,” Heard said.

This year has brought a couple of other considerations.

First, if pH testing soil this year, producers should be careful as they interpret the results, said Gao. Because there may be more salts accumulated in the soil, a test may indicate a lower-than-actual pH result.

If concerned about the result, test in spring again, said Gao. This will likely give a more accurate reading.

Second, with recent rains and warm conditions, volunteer crops are flourishing and turning fields green, said Heard. It’s a double-edged sword, he said.

The crops will capture N and ensure it won’t be lost if we get a wet fall. However, it is also using up precious water and consuming N in the soil. Heard said studies have shown producers won’t get all that N back next year because some is hidden from the crop.

Farmers will need to find the balance as to when to kill off all that greenery.

Next season

One Prairie agronomist says that having the inside track on your nutrient situation can help you manage risk going into the next production season.

Matt Gosling owns Strathmore, Alta.-based Premium Ag, and he echos the provincial soils specialists in their call for soil testing.

“There has probably never been a more critical year in my 18 years of doing agronomy to soil test,” he said. “Soil testing is probably one of the most affordable things we can do to know exactly what we have in the soil. You can’t manage what you don’t measure.”

A key decision going into a possibly dry season is size and type of crops.

“Instead of fertilizing for a 50-bushel canola crop, fertilize for a 35-bushel canola crop and if we get the water before the end of June and it looks like we have potential for a 50-bushel-or-more crop, we can fertilize for it in season after planting,” said Gosling.

There’s a reason he uses canola as his go-to crop example: its high price.

Many farmers will still be tempted to plant the water-needy crop next spring even if moisture stores aren’t replenished. But recognize that’s a risky move, he said.

“Commodity prices are another thing that is pretty hard to ignore — if (canola prices are high) it’s going to be hard not to grow canola,” he said.

“So are you going to be pulled by the influence of greed or are you going to be pulled by the influence of agronomy? I think there always has to be an intermingling of the two influences that are built into a good solid rotation.”

On the other hand, crops that cost less to grow and use less water — such as barley, flax and oats — come with risks, too, said Gosling, noting barley, for example, doesn’t do well in extreme heat.

“I don’t know if I’d want to plan on a bunch of barley going into next year even though it’s one of the cheapest crops we can grow.”

Fall and winter crops are also an option but in addition to needing enough moisture to germinate in fall, they need spring moisture.

“Fall crops are very dependent on a wet spring so if we get a wet spring the fall crop will be great. If we don’t, a fall crop might be a disaster.”

It sounds risky and it is, he said.

“But what decision in ag doesn’t come without any amount of risk?”

His final piece of advice in regard to soil testing is to hire a pro.

“I can’t stress enough the value of the agronomy profession going into a challenging season,” he said. “I think having somebody on your bench with some agronomic expertise is an invaluable service going into 2022. There’s a great big difference between a soil test and a great soil test.”

Plus self-testing can be extremely taxing.

“I’ve had a farmer try to do their own soil testing and it lasted one week. It isn’t fun for them when they’ve been sitting in a combine for weeks or months to go out there and punch a bunch of cores.”

— With files from Jeff Melchior


For more content related to drought management visit The Dry Times, where you can find a collection of stories from our family of publications as well as links to external resources to support your decisions through these difficult times.

About the author

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Geralyn Wichers

Geralyn Wichers grew up on a hobby farm near Anola, Manitoba, where her family raised cattle, pigs and chickens. Geralyn graduated from Red River College’s Creative Communications program in 2019 and was previously a reporter for The Carillon in Steinbach. Geralyn is also a published author of science fiction and fantasy novels.

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