Optimal Soil Test Resolutions: 0.5, 2, or 5 Acres?

Robert Mullen Ph.D.

Robert Mullen Ph.D.

Ph.D., CCA, CPAg.

To say Dr. Robert Mullen is passionate about agriculture would be an understatement. He holds a Bachelor of Science degree in ag business from Cameron University, along with a Master of Science degree in plant and soil science and a Ph.D. in soil science from Oklahoma State University. In addition, Dr. Mullen has been published in a variety of scientific and trade journals. But it’s not just his academic accomplishments that make him unique. It’s his unwavering ability to take complex data and — in simple terms — explain how it impacts a farmer’s bottom line. Dr. Mullen delivers the kind of insightful observations that can lead to a more profitable business. As a leading agronomy expert, Dr. Mullen has a goal to further educate farmers on best management practices that improve their yields and maximize their return on investment.

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This is a difficult answer to provide for every field and every situation. In fact, research to find this answer reveals that there is no single “right” resolution. For some fields, sampling at a resolution of 0.5 acres is economically justified, for other fields a 10-acre resolution is a better option. The optimum resolution for any given field is a function of natural variability (how many soil types are present, what is the topography like, etc.) and management induced variability (how have fertilizer applications been managed in the past, has the field ever received manure, footprint of harvesting equipment, etc.).

There is one simple guideline to consider (especially if sampling a new field), you cannot extrapolate to a finer resolution. That means if you collect information at a 10-acre resolution, you cannot determine the variability at a 2-acre resolution. Conversely, if you collect information at a 2-acre resolution you can determine the variability at a 10-acre resolution to determine if a coarser resolution is more beneficial. So, start at the finest resolution that is affordable.