Soil Testing 101

Gardening, Home & Family
on January 16, 2014
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If you’re looking to cultivate a lawn, garden or have recently moved to a new place, why not test your soil? Those little baggies of dirt from your yard can really tell a lot. Find out what you can learn from testing your soil.

Soil sampling. The process of obtaining soil for a sample amounts to digging a few inches deep and pulling up a hunk of dirt. Repeat the process all around the yard about three or four times and mix the samples. Send or deliver a cup or two to the local testing facility, like an agricultural school or garden center.

Now what? Once your soil sample testing is complete, you will have an analysis. According to Colorado State University Cooperative Extension and the Division of Reclaiming Mining and Safety, the soil report tests for many things, including pH, soluble salts, organic matter, nitrate nitrogen, phosphorus, potassium, zinc, iron, copper, manganese, lime and soil texture. Gypsum and sodium adsorption ratios may also be performed.

How to interpret results. Most reports will give you detailed data, a summary of the results, a general interpretation and advice. From these results, you can adjust the way you fertilize and otherwise manage the soil you are cultivating.

Soil test results. Routine and additional testing is commonplace when looking to understand and improve the quality of soil. The results are important when adjusting soil additives in order to reach optimum soil quality for the target plantings.

  • Soil pH results will indicate the level of acidity in the soil tested. Alkaline soils register above 7.0 on the pH scale. A result of 7.0 is a neutral soil and below 7.0 is considered acidic soil. The type of plant you grow may require a different level of soil acidity.
  • Soluble salts testing measures the level by which electricity is conducted through an extract of the soil. This test is important because each plant tolerates soluble salts differently.
  • Organic matter is measured in proportion to the soil sample. Organic matter provides most of the nitrogen in the soil — about 95 percent. Thirty pounds of nitrogen is released per acre for every 1 percent of organic matter present.
  • Nitrate nitrogen is readily available as fertilizer within the soil. Knowing how much is present in the soil will guide your nitrogen augmentation or lack thereof.
  • Phosphorous, potassium, iron, zinc, manganese and copper are measured to determine how much fertilizer is needed. A low soil test result will indicate fertilization is needed.
  • Lime is a proportional measurement. The percent of free lime within the soil is important in deciding whether to add sulfur to the soil.
  • Texture is measured by hand. The feeling of the soil — sandy, loamy or a combination — will help in deciding when to apply nitrogen.
  • Sodium adsorption ratio determines the ratio of sodium to calcium and magnesium. Excess sodium can cause hard soil that will not absorb water.
  • The gypsum test is usually conducted with the sodium adsorption test to determine if additional gypsum is required.
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