When starting a new garden, it is a good idea to learn about the soil, the source of most of the nutrients and water plants need. Plants in existing gardens can fail for a number of reasons best determined by examining the soil. Soil problems such as nutrient deficiencies and salt excess can interfere with plant health, and even cause death. These can be diagnosed by soil analyses.

While home stores and nurseries will often sell test kits for home use, they are only meant to give a rough estimate of the nutrients nitrogen, phosphorus and potassium, and pH (a measure of acidity or alkalinity). The first three are usually only given as “high, medium or low” and the pH results are rarely accurate above a level of 7.2, too low for many desert soils. These kits do not provide detailed information on other important factors, nor are they able to predict whether the soil will meet any proposed use.

When more in-depth information is required, it is necessary to send a sample to an analytical laboratory.

Usually, these laboratories are either university-based or certified commercial laboratories. Certified laboratories can recommend soil additions to make it more suitable for different purposes.

University of Nevada Cooperative Extension does not have a certified lab for soil analyses.

The customer has a number of choices to make before sending a sample to either a university or a certified commercial laboratory. It is generally better to choose a laboratory that is familiar with local soils. Selecting the right tests will depend on how the information will ultimately be used. Although the information contained in soil reports is generally similar, results are reported differently from lab to lab. It can be useful to have a guide as to what various reports contain.

Many analysis reports are designed to prescribe the fertilizer requirements for specific plants to produce in the sampled soil. For home gardens, the information can help to determine how to improve the soil, especially some western soils which are infertile, salty and alkaline.

What is in a test?

Plants have nutrient requirements just as animals do. These requirements include nitrogen, phosphorus, potassium, calcium, magnesium, manganese, zinc, iron, boron and sulfur, copper, nickel, chlorine and molybdenum, as well as carbon, hydrogen and oxygen (from the air).

While different laboratories can provide many different services, there are a few standard tests that can guide home gardeners. The order form each laboratory uses will ask what exactly the customer needs. Basic analyses usually analyze for: salinity (all salts) and sodium, pH, and several of the essential nutrients listed above.

Two results that are not always reported are the percentage of organic matter in the soil and the soil texture. If these are not part of the standard test, gardeners should request them. More tests are generally available for a fee, but may not be interesting to the home gardener.

Requesting an analysis

Although laboratories can test for the same elements and soil properties, they may not use exactly the same methods. For this reason, there can be some differences among lab results.

The application form for an analysis will often ask what crop is being grown, and may ask what fertilizer treatments have already been applied. This can be important information, for if a high dose of compost or other fertilizer was recently added, it will have an impact on test results.

When asked what crop will be grown in the soil, it is usually enough to state that it will be a “vegetable garden” or turf grass, or “ornamental (shrubs, trees) garden” on the form. When possible, ask the lab for recommendations as well as the existing concentrations of nutrients. If the site has not had a garden before, some labs appreciate information on what, if anything, had been growing there previously.

The following is a mock-up of a standard soil analysis form. Every laboratory is different, but forms generally will list prices for different tests and occasionally will provide directions for obtaining and handling samples.

For the complete article and how to understand the results use the link below.

O'Callaghan, A. 2010, How to Read a Soil Analysis Report, Extension, University of Nevada Reno, SP-10-12

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