Soil Sampling in 2017: Data Driven


Jill Scheidt, University of Missouri


Generally speaking, any ag service provider’s most important job is to help grower-customers produce more with less.

According to Jill Scheidt, a University of Missouri Extension agronomy specialist operating out of Barton County in southwest Missouri near the Kansas border, obtaining quality soil samples is a big part of being able to deliver that value for growers via accurate nutrient recommendations.

“In a 20-acre field, there are approximately 40 million pounds of soil,” she shares. “Of those 40 million pounds, you send one pound to the lab for results, so make sure that one pound represents the field well.”

Scheidt also advocates for more consistency in the process of pulling soil cores.


“Sample cores need to be at least 6-8 inches deep; too shallow of a sample can cause an overestimate of soil fertility levels,” Scheidt states. “Every core should be the same depth and quantity to provide uniformity. A zigzag pattern of random soil sampling across the field works well in most situations.”

Another often overlooked aspect of the soil sampling process is interpreting the results. Oftentimes, Scheidt shares, the soil lab report can be confusing to growers, so ag service providers should be ready to explain what the numbers mean in terms a grower will understand.

“Interpreting soil tests are the most difficult part of the process,” she says. “The first section of the soil test report represents the current level of nutrients. Macronutrients are expressed in pound per acre and micronutrients are expressed in particles per million (ppm) and rated on a scale of very low, low, medium, high, very high, to excessive. And the lower section is the recommendations of the nutrients expressed in pounds per acre, according to the desired yield goal and cropping option.”

Data-Driven Sampling

Having visited its impressive 12,000+ acre operation in Los Banos, CA, as part of our spring Ag Tech Tour in March, I figured it would be interesting to explore how an operation as crop diverse (10+ crops grown in 2017) as Bowles Farming handles its soil sampling duties.


Danny Royer, VP of Technology at Bowles Farming, characterizes the company’s soil sampling not as grid or zone-based, but as “data-driven sampling.”

Danny Royer, VP of Technology, characterizes Bowles’ soil sampling not as grid or zone-based, but as “data-driven sampling.”

“The more data we start getting, the more organized we get with our data, the more sensors we deploy, the better decisions we are going to be able to start making,” says Royer.

Organizing and georeferencing soil sample data is the job of iCropTrak’s CropTrak software, and Royer also will integrate aerial imagery from Esri’s ArcMap to create maps and run spatial analysis on the data. Then management zones are established and decisions on fertility are ready to be made.

“We’ll basically create different thresholds for what we decide is homogeneous in the field and then we’ll blend the different management zones where we can based on soil samples, and from that we’ll do variable rate mediation — which is your potash, your sulfur, compost, things like that.”

This fall Royer has plans to tinker with the farm’s irrigation sets, since pretty much all of the fertilizer Bowles puts on is delivered through the drip tape.

“I’m going to go get more detailed soil samples within irrigation sets, so if I know there is variability I will identify the variability using imagery, then I’m going to go out and target those different spots within the irrigation and sample those,” he explains. “See how different those soil sample results come back, and from that information figure out how big each zone is within that irrigation set and then come up with an aggregated way to treat that set specifically.”

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Avatar for Cory Cory says:

Sampling zones from imagery? A high biomass zone can have high or low fertility based on what it is…old yardsite needs little fertilizer whereas a high productivity midslope needs a lot. Same with low biomass…can be salinity that never needs fertilizer or a flooded out spot or an eroded hill. Biomass isnt a great soil test director.