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Soil moisture and yield

For dryland farmers, water is the most important nutrient. Find out 
how to measure yours more accurately

On average, it takes about 50,000 pounds of water to grow one bushel of wheat, says Elston Solberg, president of Agri-Trend Agrology. One bushel of canola will suck up about 70,000 to 75,000 pounds of water.

“So when it comes to dryland agriculture, and trying to balance fertility recommendations, (water) is actually, in dryland agriculture, probably the most important nutrient we’re trying to balance,” says Solberg.

Knowing how much moisture the soil has banked can help farmers make better management decisions. And many water measurement tools are free or cheap.

Free measurement tools

“I’m always flabbergasted by people who don’t actually know, on average, how much rainfall hits their farms every year,” says Solberg.

“Of course, there’s no such thing as normal. But it seems to me if you had a ballpark figure of how much rain lands on (your) farm on an annualized basis, that might be good information.”

Farmers can pull up climate normals through Environment Canada’s website. But precipitation often varies over a few miles, so it’s worth tracking precipitation right at your farm. A simple rain gauge or a met station both work fine.

“We need to start using some of these simple tools because if Grandpa’s field is 10 miles south of Ryley, and Grandma’s field is 10 miles north of Ryley, chances are the precipitation on those two fields is considerably different,” Elston says.

Knowing how much water the soil can hold, along with other soil characteristics, also helps.

When looking at soil tests, Solberg suggests first noting cation exchange capacity. Organic matter is also important, as it can influence how much water soils can hold. Soils with high PH levels can have cation exchange capacities that are skewed high.

“So don’t let that mislead you. In other words, if you have high PHs, get familiar with doing hand texturing or some other method. Go to the soil survey to get a better read on what is actually going on down there,” Solberg says.

Soil surveys are invaluable and underused. “And that’s a tragedy,” says Solberg.

Farmers can access soil surveys online by searching “cansis,” or by going directly to sis.agr.gc.ca/cansis. Solberg says the site will give you free access to “every soil survey that’s ever been done in Canada.”

Checking soil moisture

Solberg says a moisture probe is one of the most valuable tools farmers can have.

Agri-Trend Agrology sells moisture probes for about $40. A high-end model hits about $100, Solberg says, but he adds farmers can also make their own.

Saskatchewan Agriculture’s website includes instructions for building a moisture probe. Farmers can weld a three-quarter inch steel ball to the end of a rod that’s half an inch thick and 3-1/2 feet long. Welding a handle on the other end finishes the job.

Moisture probing in the fall can alert farmers to potential problems with flooding in the spring and help with planning over the winter. Checking moisture levels before spring seeding helps predict yield potential and rewrite those carefully considered winter plans.

“On November 1, one probe in a quarter section is as good as a million. In the spring it’s a different story because it’s all variable,” says Les Henry, former soil science professor and long-time Grainews contributor.

Saskatchewan Agriculture suggests sampling at least 15 to 20 sites per field. Farmers should pick representative field areas to check subsoil moisture. The probe should be pushed into the ground in a single motion. Dry soil will stop the probe.

How much water this adds up to depends on the soil texture. Saskatchewan Agriculture’s website outlines the values shown in the table.

At the other end of the technology spectrum are tools such as Aqua Check. The system monitors soil moisture at various depths throughout the day and sends updates to the farmer.

“It makes life a lot easier. (It was) originally designed primarily for irrigation farmers but I think there’s a bigger fit for these in dryland than in irrigation, mainly because in dryland we’re more reliant on the water,” says Solberg.

At the turn of this century, farmers suffered through years of drought. But the cycle has shifted in recent years.

“We’ve had three irrigation years in a row. That’s never happened in my lifetime,” says Henry. In these conditions, it’s worth knowing where the water table is. To find the table, farmers and crop advisors can dig a shallow observation well.

“I’m 72 years old and I can do it in about 20 minutes with something I can buy for $10 at the Co-op store and a soil auger,” says Henry.

For details on creating an observation well, check out Henry’s’ Feb. 11 Grainews column.

Directing resources

Tracking soil moisture and precipitation around crucial dates can help with decision-making. For example, assuming a cereal crop was seeded May 1, that crop would likely hit the four- or five-leaf stage about six weeks later. This makes June 15 the rough deadline for trying to boost yield.

Long-term climate normals, soil moisture levels, and precipitation will all play into whether farmers then decide to chase the extra yield if they get an extra rain just before June 15.

“Depends on where your risk muscle is. Are we going to get more rain after that first six weeks, or less rain? Are we going to be aggressive? Are we going to be conservative? Those are the questions that should be going through your head,” says Solberg.

Knowing what’s going on in the soil also lets farmers use resources, such as fertilizer, strategically.

“At the end of the day it’s all about this — If you have a good read on the cation exchange capacity and you know how much water’s in the soil profile, you basically can determine whether or not Grandpa’s field is a full-blown hemi or a little, squeaky Briggs and Stratton,” says Solberg. †

About the author

Field Editor

Lisa Guenther

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.

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