Zone sampling for soil tests allows for more detail, accuracy

Vague soil sampling results can provide misleading information

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Sampling soil by zone is more efficient and accurate than using grids or bulk sampling methods, an agronomist with Clark Agri Services says.

Bulk samples, having one sample for the whole field, are the simplest, yet not the most accurate when comparing to more detailed sample methods. Vague soil sample results can provide inaccurate information.

Why it matters: Soil sampling is one of the best ways for farmers to understand their soil’s nutrient requirements. Utilizing the appropriate method can get farmers the results they are looking for.

“If we were to take a bulk sample from this field, I’d basically be telling Brad he doesn’t need fertilizer. Both phosphorus (P) and potassium (K) are within the OMAFRA ‘this is adequate’; if we were to put on anything it’d just be what the corn crop is removing next year as a maintenance level,” says Johanna Lindeboom, sales agronomist with Clark Agri Service. She was explaining soil testing to attendees of the 2019 Golden Horseshoe Soil and Crop Improvement Association meeting at the end of August held at Brae Lane farms in Flamborough. Brad Nimijohn is the owner of Brae Lane Farms.

Grid sampling is a more in-depth method when compared to bulk sampling. It is done by laying a grid on the field and sampling within each square of the field — usually five, 2.5 or one acre grids are common.

“The biggest downside (to grid sampling) is that farmers assume the variability of their field is a perfect square,” says Lindeboom.

Farmers assume that as their field changes, they occur within test areas of the field.

When zone sampling, the field is sampled based on its history of variability — such as topography, yield, pH and soil type.

Bulk tests show more variability compared to zone or grid samples.

“One part of the field has seven ppm P, another one has 30. Instead of applying nothing to both, or applying the same rate to both, one needs twice as much and one needs nothing,” says Lindeboom.

Taking more detailed soil sample cores results in fertilizer expense distributed more appropriately across the field, says Lindeboom.

“It’s not necessarily about saving fertilizer or saving money, but putting the money where it needs to go and at the end of the day hopefully you are making more profit per acre with that.”

Looking at pH on a soil test is a good way to understand the importance of zone soil-sampling. Certain pH values within a soil test are important as pH can tie up nutrients within the soil.

“Looking at the pH I wouldn’t be saying to apply any lime to this field with an average of seven. That is what you get out of a bulk sample. When we start to sample more of the field you notice (a variance); one is 5.7, one is 6 — those probably could use some lime.”

When deciding which sampling method is the best fit for a farmer’s operation it narrows down to how much information the farmer wants.

“Measure what you can manage. If you are going to go through the effort of doing some really good soil sampling on your farm, have a plan of what you’re going to do next,” says Lindeboom.

It’s important farmers understand how to use the information derived from a soil sample to improve their operation.

“If you are not going to be able to have the equipment to do the things with this information it’s not worth spending the money to get the information,” says Brandon Glenney of Glenney Ag Services.

Glenney says that it’s not uncommon for his customers to go fairly in depth with their soil samples as he is able to apply their fertilizer at a variable rate.

“Because we are working with higher equipment on the other end, they don’t mind spending the dollars,” says Glenney.

Farmers using available technology, such as automated soil samplers and maps made by agronomists, such as Lindeboom, from their local retailer gives opportunity to build on their soil and profitability.

“I can log a point and I’ll be able to record where I’ve taken all of (the samples) so in three years, we can repeat that process and I think that’s really important — the consistency and the feasibility to build on what you’re measuring is key to success,” says Glenney.

About the author

Reporter

Jennifer Glenney

Jennifer is a farm reporter who lives in Cayuga, Ontario.

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