PRS-Probe: Not Just A Soil Test

PRS-Probe was designed to provide an accurate soil nutrient analysis for zero-tillage systems. Jeff Schoenau developed the Plant Root Simulator — PRS-Probe — at the University of Saskatchewan in 1992 to assess the contribution organic matter made to the success of the crop.

Ken Greer is co-owner of Western Ag Labs, the Saskatoon-based company that holds the license. He says, “In the fallow wheat system, we had extractible nitrogen and that was a great measure, but that’s not what is available under current no-till circumstances” where nutrients are released slowly and continuously over the season.

Greer uses a money analogy to describe the problem: A century ago, the amount of cash on hand a person had was highly correlated to the wealth of that person. Today, cash on hand doesn’t necessarily reflect a person’s actual wealth. People may have little or no money in their pockets, but they have debit cards, credit cards, or lines of credit that give them access to money eventually. Organic matter breaking down is like a line of credit that provides nutrient all season long. It should be included in soil nutrient analysis.

The PRS-Probe simulates the surface of the plant root and can track the intake of nutrients from the soil. It creates a picture of the soil from the “plant’s eye view.” To start, a Western Ag Labs field service rep (FSR) uses GPS to establish benchmark locations on each quarter. He or she then takes a sample of soil from one to six inches deep, including the A horizon. The soil’s profile, texture, and aggregation are assessed on the spot, and then the sample is bagged and shipped to the lab in Saskatoon.

At the lab, the sample is moistened until it’s at optimum field conditions for biological turnover. Then it’s “incubated” — warmed up to 25C to simulate spring. Two probes are inserted into the soil sample. These probes measure the nutrients that could be absorbed by a plant in that soil over the next 24-hour period. Greer describes the probes as “a soil dynamometer.” He says, “to measure an engine’s power supply, it has to be running and the soil does, too.” The microorganisms need to be “on” before you can determine the soil’s “horsepower.” Conditions can be adapted. For a field of winter wheat, the soil will be kept cooler, for example.


Western Ag Labs uses the detailed information provided by the PRS-Probe to create the PRS-Probe Nutrient Forecaster, which Greer describes as “the heart and soul” of the system.

Once the PRS-Probe has completed its measurements, the FSR and the grower work out a crop nutrition plan. Greer says the Nutrient Forecaster is “like Nintendo for farmers.” They can plug in scenarios for 17 different crops, from camelina to durum wheat, playing out all the possibilities — fertilizer prices, yield potentials, crop prices, amount of water, and amount of heat. There are 27 million possible combinations. (Interested farmers can test drive a demo on Western Ag Labs’ website.) The FSR helps the farmer build a business plan field by field. Farmers can also use the technology to “backcast,” or plug in their actual yields, rainfall, inputs, heat etc., after the harvest to test how accurate the forecast was. Greer says the backcasts are almost always plus or minus 10 per cent of the actual yield.

The technology can be used in any soil at any time. Greer says many farmers try out three or four fields the first year and then jump to the whole farm the next year. Western Ag Labs provides the service for $2 per acre, Greer says.


Tyler Neufeld farms with his brother-in-law and father, Armin, 10 miles southeast of Killarney, Man. This year, the farm is jumping from 4,000 to 6,500 acres. Their main crop is canola, but they also grow spring wheat, winter wheat, and flax. They began using the PRS-Probe and Nutrient Forecaster 10 years ago when Ken Harms, an independent agronomist based in Killarney, suggested it to them.

Over his 30 years of farming, Armin had relied on general blends for canola and wheat. At first, Tyler admits, it was hard to trust the recommendations. The first year, they used more potash, less phosphate, and less nitrogen than usual, so they weren’t sure what to expect. When their fertilizer bills went down and their yields went up eight to 10 per cent, they decided to stick with it.

Every year, each quarter is tested and is given a specific blend as determined by the Nutrient Forecaster. Blends often vary significantly. Sometimes the recommendations buck the trends. For instance, many farmers in the area apply sulphur every year, but some years the Neufelds haven’t. Occasionally they have applied micronutrients — zinc and copper —which they had never done before.

Tyler feels the approach is very balanced. Though it’s more expensive than conventional soil testing, he finds it more than pays for itself in increased yields and fertilizer savings. He also feels their crops stand up better. By comparing the tests from year to year, Neufeld says they’ve gained close, detailed pictures of each field.

Michael Carter is starting his third year of farming near Provost, Alta. He grows canola, wheat, barley, and peas on 2,500 acres. He decided to try the PRS-Probe and Nutrient Forecaster from the get-go. He likes the fact that the technology is focused on the particular needs of the plant. To him it’s more accurate than simply identifying the nutrients in the soil. He’s happy not to have the guesswork.

So far, Carter has followed the recommendations to a tee. He has used the backcasting feature, and the predictions have been bang on both years. Carter was particularly impressed with how his crops did this year. The area only had three inches of rain and he “couldn’t believe the crops that we had.” He also appreciates the fact that Western Ag Labs is not affiliated with a fertilizer company.

For more information, contact Edgar Hammermeister, Western Ag Labs’ field services manager through www.westernaglabs.comor at 306-489-2281, or contact Danielle Wildfong of Integrow Ag Consulting at [email protected]

Patty Milligan is a freelancer writer from Bon Accord, Alta.

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Patty Milligan is a freelance writer based at Bon Accord, Alta.

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