Questions to Consider Before and During Soil Sampling
Soil testing provides data on nutrient levels and pH to help producers make more informed fertilizer and lime decisions. In Arkansas, routine soil analysis is available at no cost to residents through the University of Arkansas System Division of Agriculture (UADA). The service is supported by tonnage fees collected on fertilizer and soil amendment sales.
Soil sampling is commonly conducted in the fall after harvest or in the spring before fertilizer application, with the largest number of samples submitted to the Marianna Soil Testing Laboratory during the fall months.
The usefulness of a soil-test result depends on the quality of the sample submitted. As soil sampling season gets underway, here are some questions to consider before and during sampling, along with UADA resources available to help with soil sampling and sample submission.
Questions to consider when planning soil sampling activities
☐ When was the field last sampled?
Soil testing is generally recommended every 2 to 3 years. When comparing soil-test
results over time, sampling during a similar time of year provides more consistent
comparisons.
☐ Were fertilizer, lime, or manure recently applied?
Avoid sampling immediately after these applications because the sample may not reflect
the actual soil nutrient levels.
☐ What area will the sample represent?
Select a sampling strategy, such as random, zone, or grid sampling. Collect at least
20 cores per composite sample from an area no larger than 20 acres.
☐ What depth should be sampled?
University of Arkansas fertilizer recommendations are based on samples collected at
4 inches for rice, soybean, forage crops, and pastures, and 6 inches for corn and
cotton.
☐ What management practices could affect sampling location?
Fertilizer placement, manure or poultry litter applications, tillage, and raised beds
can create areas with different soil nutrient concentrations. Consider management
practices when deciding where to collect soil cores.
Questions to consider when collecting and handling soil samples
☐ What are the soil moisture conditions?
Very dry or wet conditions can affect sampling depth, core integrity, and soil-test
results. Checking recent and forecasted weather can help determine whether conditions
are suitable for sampling. For more information on how dry soil conditions affect
soil-test results, check the blog “How Can Dry Soil Conditions Affect Soil Sampling
and Soil-Test Results?” (https://arkansascrops.uada.edu/posts/fertility/dry-soil-conditions.aspx).
☐ Are the sampling tools clean and ready to use?
Soil probes, buckets, and other sampling materials can be exposed to fertilizer, lime,
or other materials during storage or transport. Consider whether the equipment is
clean and free of residues that could contaminate the sample.
☐ Is each core being collected consistently?
Differences in surface residue, probe angle, or sampling depth can affect the portion
of the soil profile represented by each core. Consider these factors to keep core
collection consistent throughout the sampled area.
☐ Are the soil cores being thoroughly mixed?
Mixing the cores helps ensure that the portion submitted to the laboratory represents
the entire sampled area.
☐ How will samples be identified and kept organized?
When collecting multiple samples or sampling several fields, samples can be confused
or mixed up. Labeling samples immediately or using a consistent identification system
can help ensure each sample remains associated with the correct sampling area.
University of Arkansas Division of Agriculture Resources
The following resources provide additional information and assistance with soil sampling and sample submission.
- Soil sampling instructions: Step-by-step instructions and a video showing the basic process for collecting, mixing, handling, and submitting a soil sample.
- Marianna Soil Testing and Research Laboratory: The main resource for soil sample submission in Arkansas, with information and instructions for creating an account, submitting soil samples, accessing the laboratory system, and more.
- County Extension offices: Local county Extension offices can provide assistance with soil sampling and sample submission.
Acknowledgment: This Extension material was developed as part of ongoing work on soil-test variability supported by Fertilizer Tonnage Fees administered by the Arkansas Soil Test Review Board.
Authors:
- Ana Morales-Ona Smith – Assistant Professor and Extension Soil Fertility Specialist for Row Crops
- Bronc Finch – Assistant Professor and Extension Soil Fertility Specialist for Forages
- Nathan Slaton – Professor and Associate Vice President for Agriculture and Assistant Director of the Arkansas Agricultural Experiment Station
- Trent Roberts – Professor and Extension Soil Fertility Specialist