The ability to correctly interpret soil-testing results first requires some basic knowledge about gardening. In particular, you need to understand the science behind it, i.e., the chemicals and substances that play a role.
pH is a measure from 1 to 14 of hydrogen ion concentration. The presence of more ions (pH below 7.0) means more acidic soil, while the presence of less ions (pH above 7.0) means more alkaline soil. This is an important measurement because it determines the availability of nutrients.
The best pH level for an average garden is between 5.5 and 7.0. Certain types of nutrients either completely disappear or appear in excess in levels outside 5.5 and 7.0. Keep in mind that some plants grow better in these outer levels.
Seventeen nutrients are absolutely necessary for plants to grow. They get carbon, hydrogen and oxygen from air and water, but the other 14 come directly from soil. These fourteen can be grouped into two types: macronutrients and micronutrients.
The availability of macronutrients is the most important factor in regard to plant growth. Macronutrients tend to replenish naturally in soil that is left untouched and undisturbed. On farms, however, so many micronutrients are removed during crop harvesting that farmers must use heavy doses of fertilizer to replenish them.
The six most important macronutrients are nitrogen, potassium, phosphorus, calcium, magnesium and sulfur.
- Nitrogen is especially important because it’s a component of protein. As a result, plants not exposed to enough nitrogen experience stunted growth and chlorosis.
- Potassium is important because it roles a role in water regulation. It basically helps ensure a minimal level of water loss.
- Phosphorus is important for bioenergetics. It’s needed by plants to convert the energy of the sun into chemical energy during the process of photosynthesis.
- Calcium is important because it activates certain enzymes, and it helps regulate the movement of other nutrients throughout the plant.
- Magnesium is important because it’s an essential part of chlorophyll, a pigment that plays an extraordinarily important role in photosynthesis.
- Sulfur is important because like phosphorus, it plays an important role in the process of photosynthesis. In particular, it helps in the construction of chloroplasts.
Micronutrients are important because they play a helping role in important plant processes. The eight most important micronutrients are boron, chlorine, iron, manganese, copper, zinc, nickel and molybdenum.
- Boron plays an important role in cell division and sugar transport.
- Iron functions as an enzyme cofactor during photosynthesis.
- Molybdenum functions as a cofactor during the production of amino acids.
- The rest play a role of some sort in photosynthesis.
Organic matter refers to living and/or composed animal or plant tissue that put into soil to help plants grow. Examples of organic matter include dead leaves, manure, compost and plant roots.
SAR refers to the sodium absorption rate. It measures the quantity of sodium in comparison to other relevant substances like magnesium and calcium. A high SAR is bad, as it can impact water transport. The SAR rate should ideally be under 10.
Electricity conductivity of soil is a measurement of soil salinity. A plant’s sensitivity to salinity varies wildly. As an example, beans, carrots, peas and onions can only tolerate low salinity levels, while lettuce, tomatoes and sweet corn can tackle higher levels. Zucchini, beets and artichokes can tolerate even higher levels.
Unfortunately, this list represents only the most important elements of a soil testing report. Plus, not all soil tests are the same. Laboratories differ in how they approach soil testing. Some focus more on chemical elements, while others focus more on organic elements.