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Soil Testing

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Without a soil analysis, it’s nearly impossible to tell what your soil needs to help your crop grow. A laboratory soil analysis, or a soil test, provides information on the capacity of your soil to supply adequate nutrients. This helps you select the correct mix of fertilizer and liming materials, which can help you to develop and maintain your soil and increase crop production. EC 628    Revised October 2018

Why should I collect a soil sample?

A soil sample can help:

  • Establish baseline soil nutrient status for new landowners
  • Determine nutrient application recommendations
  • Assess pH and the need for liming
  • Measure change in soil nutrient status over time
  • Document soil nutrient management for certification requirements
  • Avoid excessive nutrient applications or soluble salt accumulation
  • Develop a plan for possible variable-rate fertilizing within a field

When should I collect my soil sample?

For annual crops, such as vegetables, test soils when you first cultivate a field or change crops or rotations. If you plant successive crops in a single season, you don’t need to test before each planting.

For perennial crops, such as orchards, tree plantations, alfalfa, grass seed, and permanent pasture, the most important time to test the soil is before planting so necessary nutrients can be incorporated into the soil. If you plan to compare soil test results with the results of a leaf analysis, take samples in August.

In high rainfall areas of western Washington, soils are likely to be acidic and require periodic liming. Testing these soils in the late summer or fall allows time for these amendments to react with the soil before the following growing season.

How often should I collect a soil sample?

Soils should be analyzed often enough to recognize potential nutrient management issues before they adversely impact plant growth. In general, test every 2 to 3 years for annual crops, pastures, and legumes, and test every 3 to 5 years for Christmas trees, fruit and nut trees, berries, and grapes. Take samples at the same time of year so results are comparable from year to year.

Where should I collect a soil sample?

The area from which to collect a soil sample may depend on the soil type, topography, crops grown, management history, or all of the above. For example, a farm that has three separate sampling areas: A (orchard), B (pasture), and C (vegetable row crops), a separate soil sample should be collected from each of the three areas. The same concept applies to smaller acreages; for example, a lawn and a vegetable garden should each be sampled separately.

Follow the links below to learn how to take a sample, where to send the sample, and how to interpret the results.

Video: How to take a soil sample

Agricultural Labs

Guide to taking soil samples for farms and gardens

Home Gardeners guide to soils and fertilizing

Understanding soil tests

WSU Puyallup Soil Management

Kiley Smith provides support for small farms and commercial agricultural producers throughout the county. E-mail Kiley Smith or contact her by phone (360) 482-2934.[/textblock][/column][/row]