Conductivity (Ergs):

Energy in the soil is measured as electrical conductivity (EC) or energy released per gram of soil (ERGS) using a mixture of soil & distilled water. It is measured in grams/sec. This test will tell you if there is enough energy reaction going on in the soil to grow a plant. It will change during the growing season. If it is too low, it means not enough energy is being released. If it is too high, then there is more energy coming out of the ground than the plant can handle. At pollination time the ergs should reach the maximum needed.

Plant growth depends on quantity of mobile ions from soil and water extract. Theoretically, the ions registered by conductivity meter are small & mobile enough to be available to plants. Any complexed ions (large arrays of simple ions) will not be counted by the meter. However, if soil contains an active variety of healthy microbes, they will break down large ion clusters.

Good humus levels keeps electrical conductance “check”. When humus levels are high the ERGS reading is stabilized and does not “climb the highest peak and then plunge to the deepest valley.” When striving for high yields on soils with low humus levels, it is important to keep the ERGS up. As the growing season progresses plants draw heavily on soil reserves, taking up soluble nutrients, and the Ergs reading drops. Low soil energy causes plant growth to slow down.

Exchangeable Sodium Percent (ESP)

The degree of saturation of the soil exchange complex with sodium. High ESP’s can cause high soil pH, sodium toxicity to sensitive plants, surface sealing, crusting, and drainage problems, reduced infiltration, permeability, and nutrient imbalances/deficiencies. The lower the salinity, the more severe the problems (especially with ECe < 1.0 - 0.5 mmhos/cm).

A ESP value of 5 or less is desired, while values between 6 - 9 mean increasing problems with reduced infiltration/permeability, especially in clayey soils with low ECe (i.e., low soil salinity). ESP values > 13 generally mean severe problems for most soils (with the exception of sandy soils).

Where elevated levels are found, soil amendments such as gypsum or elemental sulfur are applied. Actual amounts of soil amendments should be based on the ESP, exchangeable sodium ppm level to be reduced to, soil depth to be remediated, and product purity.

Formazan Test:

For the last several years International Ag Labs has performed a soil test known as the Formazan test that answers the question “What is the digestive capacity of my soil?” This is a significant question that needs an answer when working with rock powders and plant residues used in organics and biological agriculture.

The Formazan test provides the biology in a soil sample with a specific amount of a food supply and waits a specific amount of time. We then measure the amount of metabolic enzymes given off by the bacterial and fungal species when they are active. The Formazan test is like the speedometer reading of microbial activity in the soil. It is an indirect microbial assay that gives us a picture of the forest—not the individual trees. Typical soils farmed with herbicides and pesticides will have a microbial activity level of less than 200 on the Formazan test. Biologically farmed soils that still use herbicides typically run from 300-500. International Ag Labs shoots for a Formazan reading of 600 as an entry-level good. At this level rock powders will be worked upon by soil biology and slowly made available. For organic soil we recommend a Formazan reading of 1,000 or greater since many nutrients in organic production must first be digested by soil biology. A Formazan reading greater than 2,000 represents a terrific soil with plenty of digestive capacity.

The Formazan test was developed by member of the Soil Science Society of America. Skujins*, who did a lot of original research on this test, found that the Formazan test directly corresponds to CO2 release, proteolytic activity, and nitrification potential. What this means in plain English is that low Formazan readings indicate a poor cycling of carbon, less microbial activity, and the inability of soil to break down organic inputs to supply plants with available nitrogen. This is very significant for organic farmers since all organic nitrogen fertilizers, with the exception of Chilean nitrate, require proteolytic activity and nitrification in order to make it available to plants. One last thing on the Formazan test, guess what the reagent or “food supply” is when incubating the Formazan test. CaCO3, that’s right—a fine grade of calcium carbonate. Surprise. Surprise.

Soluble Salts, Salts in Solution

Refers to the inorganic soil constituents (ions) that are dissolved in the soil water.

Measurement of the electrical conductivity of a soil extract gives an indication of the total concentration of soluble salts in the soil. The electrical conductivity measurement is reported in units of millimhos per centimeter (mmhos/cm).

A soluble salt test should be taken as part of any fertility and soil analysis program.

Soluble salt levels in the soil are important, because high soluble salts can reduce water uptake by plants, restrict root growth, cause burning of the foliage, inhibit flowering, and limit fruit and vegetable yields. Seed germination and seedling growth are more sensitive to salt stress than the growth of mature plants.

In well-drained soils, leaching with good quality water will help to correct soluble salt problems. Incorporation of gypsum (calcium sulfate) at the rate of 10 to 15 lbs./100 sq. ft. followed by leaching with good quality water can also be used. Gypsum is most effective in situations where sodium is the cause of high soluble salts.

High levels of sodium in the soil will tend to disperse soil particles, resulting in poor soil structure and making water infiltration difficult. The calcium in gypsum will displace sodium and the sodium will then move (leach) out of the soil profile with irrigation water and/or rainfall. Soils high in calcium have better structure than those high in sodium.

Solute

A substance that is dissolved in a solvent. One of the two parts (along with solvent) which make up a solution.

The soil solution is an aqueous liquid found within a soil. This liquid normally contains ions (any element with a negative charge, N, S, P) released from mineral particles, organic matter or plant roots and leaves.