How to Collect a Soil Sample

A soil sample can help you best determine if your soils are deficient or in excess of several essential nutrients. With that knowledge you can determine if any fertilization is necessary and exactly what you need to apply. This helps over fertilizing, one of the largest causes of water pollution. Soil samples can be used to tell if the soil is unfit for planting, due to the presence of contaminants.

Representative Sample

A soil sample must represent the area being sampled. Using a soil probe, spade or trowel, collect 10-12 samples in a random or zigzag pattern. If soil texture or sites have been treated differently (i.e. on area has been fertilized) collect a separate sample.

Sampling Depth

Depth varies according to the crop. Turfgrass samples should be taken to a depth of 3 inches; others to a depth of 6-8 inches. Discard plant material, thatch and stones. Do not sample areas that have been treated with fertilizer or lime within the last 4 weeks.

Collection

Collect Cores or slices in a clean plastic bucket and mix well. (Do not use a metal bucket) Transfer 1 to 2 cups of soil to labeled soil bags. Two cups of soil is required for nutrient and texture analysis.

Bag & Label

An approved soil sample bag must be used, most labs provide pre-printed bags. Be sure to completely fill out the entire label including city and state. Be sure to label plant and turf species on the label as well. Place soil bag in a zippered plastic bag to prevent soil spillage in transport.

Frequency of Sampling

A soil nutrient analysis should be performed on sites every 3 to 4 years or more frequently where plants are in poor health.

Shipping

Soil samples do not degrade and can be sent via mail. No need to overnight the sample.

Soil Tests Vary

Sample analysis can vary from one lab to another. Here are a few examples

  • Basic soil nutrients: pH, organic matter, P, K, Ca, Mg, CEC
  • Basic + Micronutrients: Basic information plus Fe, Mn, Zn, Cu
  • Complete: Basic and micronutrients plus Nitrate N, Na, S, B, and soluble salts
  • Soluble salts (conductivity)
  • Soil Texture – % sand, silt, and clay

Special Tests

Most agriculture soil testing facilities do not routinely test for heavy metals, herbicides or other soil contaminants. Those test are specialized and can be expensive. If you suspect there could be contamination issues I would recommend asking for the special testing to be done.

Laboratories

If you are unfamiliar with a laboratory, contact your local land grant university extension agency. For those of you in the Pacific Northwest, I have done the legwork for you:

Washington State University
WSU Puyallup R.E.C.
Plant & Insect Diagnostic Lab
7612 Pioneer Way East
Puyallup, WA 98371-4998
Oregon State University
OSU Plant Clinic
1089 Cordley Hall
Oregon State University
Corvalis, OR 97331-2093
B.C. Ministry of Agriculture and Lands (BCMAL)
Plant Diagnostic Laboratory
Abbotsford Agriculture Centre
1767 Angus Campbell Road
Abbotford, British Columbia V3G 2M3