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Soil Sample Collection Guide
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Quality Improvement Laboratory

SOIL SAMPLE COLLECTION GUIDE

General Tips
Soil samples must be collected properly and carefully to be useful for evaluating the nutrient status of a crop. Analytical results can only be as accurate as the sample. The most critical objective of sample collection is ensuring that it is representative of the area in question. If a field, orchard, or vineyard is not uniform, separate samples from each distinct area are recommended. Areas that differ in slope, color, drainage, or texture should be sampled separately if they can be fertilized separately. Avoid sampling fertilizer bands, fencerows, wet spots, severely eroded areas, or any atypical sections unless specifically evaluating these distinct locations.

Generally, try to sample when soil is relatively dry. Avoid collecting samples immediately after fertilizer application or after watering or a heavy rainfall, as misleading or inaccurate analyses may result. Best sample collection method depends on the type of plant or crop, tillage practices, and fertilization strategies. Recommendations for some situations are listed on this page. Please contact our lab for sample collection recommendations for other types of crops or strategies.

Sample Collection Tools
Use stainless steel or chrome-plated sampling tools and plastic buckets to avoid contaminating samples with traces of microelements from the tools. Avoid brass, bronze, or galvanized tools. Tools should be clean and free of chemical, lime, or fertilizer residue. A trace amount of residue can seriously contaminate the sample and cause inaccurate results.
Soil samples may be taken with a soil tube, auger, narrow-bladed trowel, or a spade. At each sampling site, scrape away surface debris and remove a core sample to the appropriate depth. If using a spade, dig a spadeful of soil to the appropriate depth and discard it. Then take a 1-inch slice of soil from top to bottom. Keep the entire slice or keep only a strip from the middle of the slice, top to bottom.

Sampling Depth
In general, soil samples should be taken from the root zone of the crop in question. For field crops, sample soil to the depth that the field is plowed, usually 0 to 8 inches. This zone is where lime and fertilizer have been incorporated. Where no-till conservation-type tillage systems are used, collect a second sample at a depth of 0 to 4 inches. Also sample from 0 to 4 inches for pastures, turf, and forage fields. Studies have shown that for most orchard crops, depths of 8 to 14 inches are best. For home gardens, sample soil from 0 to 6 inches. To sample subsoil, which is recommended every 2 to 3 years, sample 6 inches beyond the root zone of the crop. Be careful to maintain a constant depth for all samples collected for best results.

Number of Samples
The number of samples that should be collected depends on your overall nutrient management strategy. Conventional, whole-field management usually requires less sampling than a more systematic, site-specific or grid sampling approach. Choose a system that best fits your strategy.

Whole-Field Nutrient Management
Traditional whole-field management requires only enough samples to determine the average nutrient concentrations for the field. Collect 15 to 20 soil cores or aliquots taken at random locations and combine them into one sample. Thoroughly mix and subsample the composite sample if necessary. Generally, one sample should represent a uniform area of not more than 20 acres. Place the sample in a clearly-labeled Soil Sample Bag and submit to the lab within 48 hours for best results.

Site-Specific Nutrient Management
Site-specific soil sampling is more labor-intensive than whole-field sampling. The objective is to accurately describe the size and shape of each soil condition or property to allow variable rate application of nutrients and other inputs. A field is mapped and divided into blocks or cells to form a grid. Using GPS software, a random sampling location within each grid cell is identified and sampled. Results are incorporated back into the mapping software and used to manage nutrient applications. Recommendations for number of samples per field depend upon the nature of variability within the field. Generally, one sample per acre or 200-foot cell widths are recommended to begin. Many high-value crops are sampled using 100-foot grids. Sample each grid cell as mapped. Place samples in a clearly-labeled Soil Sample Bag and submit them to the lab within 48 hours for best results.


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