Getting Into Soil Testing

Tuesday, April 21, 2026

Taking the guesswork out of your fertilizer program

By Emily McKinlay

Soil testing is like going to the doctor for a checkup, says farmer and CCA Derrick Leclair. Soil testing can help producers get more out of their crop and keep their soil healthy by taking the guesswork out of their fertilizer program.

“Sometimes you need a soil test when something goes wrong, but sometimes you just need a checkup. You can check to see how the nutrients are balanced and if anything is out of whack,” says Leclair, who runs a part-time soil testing service in addition to crop farming near Dresden, Ont.

Mark Wagner, an agronomist at Down to Earth Labs in Lethbridge, Alta., says that soil tests can help producers find a balance between cost and yield improvements.

“For growers, it always comes down to costs, profits, and yields,” says Wagner.

“Doing a soil test can reduce any unnecessary fertilizer purchases by telling us which nutrients are sufficient and deficient and how much we actually need for good fertility management. This leads to cost savings and could help producers get better yields, if everything lines up for fertility and weather conditions in the growing season.”

Getting started

To get meaningful results, a soil test starts with a sample representative of the farm and its soil.

“I typically see testing every year after the crops come off,” says Wagner.

“Usually, producers will wait until the soil cools a bit to ensure less change in nutrients. Different farms have different soil-testing strategies. Some do full testing of macronutrients and micronutrients. Micronutrients are influenced more by climate and weather, and macronutrients by crop utilization. Some farmers do everything yearly, or others will test macronutrients every year and micronutrients every few years.”

Maintaining a schedule for sampling allows producers to regularly track the change in nutrients in the soil.

Leclair uses a few different strategies to get a representative soil sample from each farm.

“You can take a composite bulk sample to represent up to 25 acres, and that gives you an idea of what’s in your soil, but obviously, within 25 acres, there can be a lot of variability,” says Leclair.

“I like to focus on grid or zone sampling. You can drop points around the field with GPS and go to those points and sample the area around the side-by-side for around two to five acres. Or what I often do is criss-cross across the grid, covering the corners and the middle across that grid square.

“But even within that, you can have different soil types. My favourite method is to zone sample using layer data. I trace different areas — using yield, elevation, or soil types — and those zones can be any shape. You utilize that data to find the variability in the field.”

Wagner adds, “If the field has relatively uniform topography, some people will take composite samples across the field and mix and combine them to get a good average. In fields with variety, drainage issues, or texture differences, or topography, they might sample in zones.”

Producers might also choose to sample different depths, to get a clearer picture of soil stratification.

Interpreting results

Once the sample has been sent away and the results are in, there can be a lot of information to sort through.

Many producers will have a trusted agronomist with whom they work to create a fertilizer plan. Conversations with agronomists are a good opportunity to learn what to look for in soil test results. Some farmers may create their own fertility plan as well.

“Some producers have their own agronomist, or some do their own planning,” says Wagner.

“If you have a typical crop rotation, knowing the next crop in the rotation will determine if the results indicate that you have sufficient nutrients, as well as how much fertilizer you need to apply or if you have an adequate amount of fertility already.”

Different farmers will have different measurements that are critical to their crops.

“In Lethbridge, we have a lot of potato growers. They are fairly focused on the nitrogen amounts and need to prepare their soils properly,” says Wagner.

“Know your soil and how it behaves — if it leaches or erodes — because that can help with decisions on soil placement and how much fertilizer you need to put down. If you’re in a high clay farming area, the nutrients will hold on and not leach as much compared to sandy soils that will leach more nutrients. Fertility is always changing with each crop that’s harvested.”

When reviewing soil test results, Leclair starts with nutrients that are often lacking.

“Personally, I look for the low-hanging fruit, like single-digit phosphorus using the Olsen/bicarb test. If phosphorus is below 10 ppm or potash is below 100 ppm, that’s a common area of concern,” says Leclair.

Leclair also looks for variation across fields.

“I often look at cation exchange capacity (CEC). A higher CEC indicates more clay content and heavier soils, and sandier soils have a lower CEC,” says Leclair.

Wagner also recommends assessing organic matter levels, pH, and conductivity.

“In the western Prairies and in dryland areas, there is a trend of field pH lowering and of soil becoming more acidic in patches. That could be an issue with composite soil samples. Some areas could have a pH of seven or eight, but low areas might have a pH in the mid-fours,” says Wagner.

“Look at conductivity and soluble salts. Some fields could have saline issues, or if you are pulling water from wells, you could have salt in your water. It’s expensive to mitigate those problems, but it’s good to keep an eye on them, and if you see them trending up, it’s good to be proactive and address them before it becomes expensive.”

Applying on-farm

To see the payoff of a soil test, producers need to apply the results to their crop plan.

One of the primary outcomes of a soil test is information to determine if the soil can support the intended crop rotation. Producers should know their expected yields to estimate crop nutrient removal rates and compare them to the soil results.

“Some farms would typically aim for certain yields, and some crop input companies will post average yields for districts and zones, which can be a good reference for a target yield in that area,” says Wagner.

“Some people also have a farming group, like Potato Growers of Alberta, that could share benchmark yields. Others will know their fields well and know how they are likely to perform. With irrigation, it’s easier to be consistent with yield than in dryland areas.”

Leclair adds, “It can be good to do a crop nutrient management plan. You can punch in your yield goal and see how much the crop removes from your soil, and comparatively, if that is going to drop your soil test levels too low.”

Producers can then use this information to decide whether to replace nutrients at crop removal rates or to make an effort to build soil. They can also use this information to build specific zones if they have access to variable-rate application.

“If you are applying the same rate across the whole field, you could be putting fertilizer on where you don’t need it, or you could have less in areas where you do need it,” says Leclair.

“With the price of commodities now, it doesn’t make sense to put the same rate across the field. We are trying to be more efficient because they don’t give that stuff away anymore.” BF