soil sampling - growers precision agtech

A Quick Guide to Better Soil Sampling

By Cole Condra – Customer Success Manager

Soil sampling every year is the best way to gauge your soil nutrient values and eliminate unnecessary fertilizer applications. 

In this guide, you’ll learn whether zone or grid sampling is better for you, which soil collection method is the best, and how to keep soil samples consistent.

Zone vs. Grid Sampling

It’s an ongoing debate about whether zone or grid sampling is the best method for collecting soil samples (and both have advantages and disadvantages).

For zone-based soil sampling, you first need to determine how you’ll create your zones. You can base zones on a variety of factors, such as historical yield data, soil electrical conductivity (EC), aerial imagery, etc.

EC mapping has gained popularity because it’s a relatively inexpensive way to gather high-resolution spatial data on the soil. Mapping soil EC adds time in the field before soil collection can start, but it’s a way to capture soil variability, so the zones you create have similar soil characteristics.

You can learn more about why we prefer zone sampling here.

Due to the need to take more soil samples within a field, grid-based soil sampling can be more expensive and time-consuming. Sizing of the grids can also vary based on the farm. While the most common sizes are one or 2.5-acre grids, farmers also use 4.4 and 10-acre grids at times.

Variability within the soil can be captured by creating grid sizes that are smaller than the size of typical zones. Even though grid sizes are smaller and you must take more samples, you save time by overlaying a grid on the field and immediately sampling.

The 4 Types of Soil Collection 

There are multiple methods to retrieve the soil samples, including hand sampling, hydraulic probes, electric probes, and auger probes. Here are the pros and cons of all four of the most common methods:

Hand Sampling

Pros:

  • Ease of use
  • Lowest initial investment
  • Fewer components
  • Little to no maintenance
  • You can see and adjust for sampling depth

Cons:

  • Time-consuming
  • Labor intensive
  • Difficulty keeping sampling depth consistent (hard vs. soft ground and time spent sampling)

Hydraulic Probes

Pros:

  • Faster and more consistent (set sampling depth)
  • Easier to get into the ground (hard and soft ground)
  • Not as labor-intensive
  • Hydraulics, in general, are more durable than electric and generally come with multiple spin settings (better suited for multiple soil types)

Cons:

  • Lots of components (engine, hydraulics (tank, pump &  lines), probe, etc.)
  • Noisy
  • Higher initial investment ($4 to $8k average)
  • Fabricated equipment to mount probe; all parts are company-specific


Electric Probes

Pros:

  • Quiet
  • Fewer components (probe and battery only)
  • More consistent (set sampling depth)
  • Less maintenance
  • No fuel cost
  • Easy setup
  • More suited for dusty conditions
  • You can purchase most electronic parts off the shelf

Cons:

  • Various electrical parts
  • Slower cycle time
  • Not as powerful as hydraulics (hard ground)
  • Usually, only come with a straight up and down setting
  • Battery drains more quickly with repeated use

Auger Probes

Pros:

  • Ease of use in harder ground
  • Easy setup (hand tool auger)
  • Probe is more durable than hydraulic and electric probes
  • Fewer components (hand or side mount probe)

Cons:

  • Probe cleanout is poor (cross-contamination very likely)
  • Slower cycle time than hydraulic
  • Usually does not work well in sandy soils
  • Hard to verify core depth

While farmers will never agree on the perfect way to sample soil, the availability of options allows them to use the management and collection methods that work best. Based on the pros and cons of each, you can determine which tools will help you collect soil samples easily and accurately on your farm.

How to Take Consistent Soil Samples

Regardless of the method you choose, to get the best results, be consistent with your soil sampling. Below, we’ve included the six most critical steps you should take:

  1. Always make sure your soil cup is clean before moving from one zone/grid to another within a field and before sampling a different field. 
  2. Be sure the soil core depth remains the same throughout the sampling process.
  3. Take the same number of cores in each zone/grid for every field.
  4. When filling your soil bag, always keep the amount in each bag consistent. Most soil bags will have a “fill to here” line on them, but in case yours doesn’t, make sure every bag has the same amount.
  5. Be sure each bag is labeled correctly. Whether you’re handwriting your soil bags or using labels, ALWAYS check to make sure you have the correct Grower, Farm, and Field with the correct spelling.
  6. Finally, verify that you have the correct bag number for your current zone/grid before filling it.

Need help with soil sampling on your farm? Contact Growers at 984.500.3797.