What a Home Soil Test Will Not Tell

A professional soil test is an excellent tool for analyzing deficiencies, excesses, and the relative balance of all plant nutrients in your garden's soil. A home test kit, however, is very limited and only points out pH level and deficiencies of nitrogen, phosphorus, and potassium. If you have difficulty growing healthy plants in your garden, a home test kit may not provide the solution. Plants grown in soil lacking any of the major or trace minerals show their deficiency in yellowed leaves, stunted growth, purple veins, or any number of other ways.

7. Joseph A. Cocannouer, Farming with Nature (Norman, OK: University of Oklahoma Press, 1954), p. 50.

SOIL pH SCALE

acid neutral alkaline pH

A pH reading tells you the relative acidity or alkalinity of the soil water, generally called the soil solution. Nutrient availability for vegetable plants, soil microbial activity, and soil structure are all affected by pH. Most vegetables grow best in a slightly acidic soil with a pH of 6.8. A range of 6.0 to 7.0 is fine for most crops.

More important than the actual pH reading is the quality of the pH. This is determined by testing for the amount of plant-available potassium, magnesium, calcium, and sodium in your soil. Only a professional soil test can determine the soil's mineral balance. You should have this information before you apply pH modifiers to your soil. For instance, limestone is a common pH modifier; however, all limestones do not have the same mineral composition. An application of a dolomitic instead of a calcitic lime to a soil with a high magnesium content could disrupt your soil balance and adversely affect plant growth.

Soil-applied organic matter and manure can alter the pH over time. When adequate organic matter is used, we find crops will tolerate a wider pH range. Leaf mold, pine needles, and sawdust produce an acidic compost that can lower the pH. Manures may be alkaline and raise the pH, although they may lower the pH one point in some cases. Compost can be either acidic or alkaline. Using the proper limestone with the correct mineral balance is the least expensive and most practical way to increase pH. Mined sulfur, a soil nutrient deficient in many soils, is an excellent amendment to lower the pH. Although you can use organic matter to alter pH, you will need to know your soil mineral structure, the existing soil pH, and the pH of the applied material in order to apply it accurately and in an effective amount.

The Analysis of Recommended Organic Soil Amendments, beginning on page 53, gives the mineral nutrient content of many commonly used organic fertilizers. This information will help you determine the amounts of each fertilizer to add if you are using a home test kit and are unable to have a professional soil test performed. In your calculations, it is not necessary to subtract the nutrients you add to the soil in the form of manure and compost. Be careful, though, about adding manure. Much aged or composted manure actually contains little nitrogen and may have a substantial amount of nitrogen-demanding sawdust. If you use a lot of manure containing large amounts of sawdust as a soil texturizer, you may want to add some additional nitrogen fertilizer, such as 4 extra pounds of alfalfa meal per 100 square feet. (Notice that the release times are different for different fertilizers.)

Broadcasting fertilizers.

Broadcasting fertilizers.

Organic Gardeners Composting

Organic Gardeners Composting

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Responses

  • Malva
    How to determine the ph of soil at home?
    8 years ago

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