Soil Sampling Methodology

Why does the methodology matter?

Soil sampling methodologies can often provide vastly different results for soil taken from the same location. The number of samples taken, location & depth of samples, and time of year are all variables that can impact the lab results, as well as variance between testing labs.

In order to use the information effectively, farmers must understand the methodology that was used and work with a knowledgeable consultant to identify the key factors that should be addressed in their fields. Likewise, a soil sample is really a mere snapshot in time of that field and thus should be used in conjunction with other supporting data (yield, nutrient application, etc.) to make effective operational decisions.

At The Soil Foundry, we tailor our services to complement each farmer’s management style, skill set, and priorities. To determine the best soil sampling methodology, we take into account the following factors:

Field Variability (Soil Fertility)

  • Soil type
  • Terrain / Drainage / Tiling
  • Past practices / Crop rotation / Philosophy

Layout of Sample Locations

  • Gridded method (1.1, 2.5, 3.3, 4.4, 5.0, etc.)
  • By soil type
  • Modified grid
  • By zone / composites
  • Veris (electrical conductivity)
  • Combination of the above

Soil Sample Depth

  • Depends on state Land Grant recommendation
  • 6”, 7”, 8”, 9” other
  • Depends on the crop classification
  • Used in developing the calibration data set to be used in interpreting the soil tests

Number of Samples

  • Number of cores collected at each sample point
  • State recommendations (5 to 7 / possibly more)
  • Are the cores composited?
  • Are we taking enough samples?

Sampling Frequency

  • 3-4 years. Very common practice.
  • 2 years. Due to higher yields and changing climate patterns, more thought being put into testing more frequently. Improves in managing variability in field.
  • 1 year. Rare, but some have adopted this intensive program to assure maximum returns. Planned expense.

Season to Test

  • Fall sampling time frame has become more compressed as harvest pace quickens
  • Testing season has been shortened to about 6 intense weeks; 2 of those being very challenging
  • There is increased interest in moving to spring sampling strategy
  • Much of the original calibration data for recommendations was actually done in the spring season
  • Allows crop refuge to break down and release any nutrients within stalks / plant material
  • Allows time to get sampling done, figure product requirements, set up recs, set up logistics (not chase combines)
  • Most labs offer spring discounts on pricing

Long-Term Outlook

  • What is the grower’s long-term outlook for the field to be tested?
  • Cash-renting?
  • Tenure period?
  • What is the past history?
  • Value of Land
  • Cost of Fertilizer
  • Value of the Crop