Soil Sampling Instructions

The King Conservation District recommends that land managers sample and test their soils regularly. Whether you are growing forage for livestock, gardening, maintaining an orchard or managing a woodlot for wood production, proper soil sampling will allow you to:

• Apply the correct amount of fertilizer for the plants you are growing.

• Prevent surface and ground water from being contaminated by excess fertilizers.

• Ensure that soil nutrients and other conditions (such as soil acidity) affecting plant growth are present in the right amounts.

Results of soil nutrient management can include:

• Increased plant growth, yields and quality.

• Less purchased livestock feed and fertilizer.

• Better utilization of manure on your pastures, lawns and gardens.

How to take a sample

Avoid sampling when soils are very wet (winter and early spring) or within a few weeks after applying lime, fertilizer, compost or aged manure.

You should take samples from areas with differences in soil textures (i.e.  clay, sand, silt, gravel, muck), topography, drainage, color, productivity or where plant growth is poor. To make sure that your samples are representative, take at least 15 small samples (called sub-samples) across the whole sample area. Avoid taking sub-samples from areas of obvious nutrient concentration (such as cow pies), or areas that are noticeably unusual.  

You will need a spade or hand trowel (stainless steel or wood), a clean plastic container and a sampling bag (a ziploc bag will work). Take thin slices of soils to the depths indicated in the table below and put them in the container. Thoroughly mix the sub-samples and put two cups of soil into the sample bag.

Dried vs. Wet Samples

Soil nutrient levels continue to change even after a sample is taken, due to microbiological activity. Therefore, it is critical that this activity be stopped as soon as possible after sampling (within 12 hours). Drying soil in a low temperature oven (100 F) is sufficient to stabilize the sample nutrients. You can dry the sample in a glass or aluminum pan, stirring occasionally until no moisture remains. As an alternative to drying, you can also freeze your sample to stop microbiological activities.  

If you are using our Soil Nutrient Testing Service, bring or send your sample to our office:

Attn: Soil Testing
King Conservation District
1107 SW Grady Way, Ste 130
Renton, WA 98057

If you are sending directly to a lab, contact the selected lab for any additional information requirements that the lab might have.

We send our samples for a basic analysis that include phosphorus, and potassium, lime (pH), nitrate-nitrogen (fall only) and micronutrients. The lab report will include fertilizer and lime application recommendations for your desired crop yields.

Basic Sampling Guidelines

• Sample three to twelve inches in depth (depending on the time of year and type of crop) for each sub-sample.

• Take a minimum of 15 sub-samples per sample area.

• Mix all sub-samples well.

• Take two cups of soil for each bagged sample area.

• Label each sample with the following:

• Name

• Address

• Phone Number

• Sample date

• Five letters and/or numbers (i.e. PSTR1) that will help you remember where the sample came from.

• What you plan to grow in the sample area.

• Send the sample in right away. Consider drying or freezing the samples to stabilize nutrient levels.

For additional information, contact Jay Mirro by phone at (425) 282-1905 or by email at Jay Mirro