Tilth, soil carbon and biological activity measurements

 

Three tests can be helpful in further assessing your soil health: tilth measurement, total soil carbon and biological activity:
 

Test

Description
Tilth measurement
Tilth can be measured by calculating soil density. You can measure tilth by weighing out 100 grams of dry soil and noting the volume it occupies in a measuring vessel. The weight divided by the volume will give the soil density in grams per cubic centimeter.
 
Total soil carbon
Total soil carbon is measured in a lab by igniting a soil sample of known weight, weighing the dry remains and then calculating the weight lost to determine the amount of soil carbon in the sample. Since soil organic matter is approximately 50% carbon by weight, doubling soil carbon values gives a good approximation of soil organic matter.
 
Biological activity
Biological activity involves measuring soil respiration, or the release of carbon dioxide.   "What you are measuring in the breathing of the soil is the activity of the microorganisms and their ability to break down soil organic matter," Paul Hepperly, TRI research manager explains. "This is done by measuring the release of carbon dioxide, which is a decompositional gas. It's the opposite of photosynthesis."
 
 

 

 

 Research

Dr. Ray Weil has developed an inexpensive, easy-to-use kit to help farmers determine the active organic matter fraction in their soil. Remember, when soil is mismanaged, active organic matter is the type that is lost first. Farmers can use the test to determine which of their fields need the most urgent input of organic materials.

Using the kit, you can mix a solution of potassium permanganate with soil, then use the color of the solution to determine active organic matter. The only expensive component is the hand- held colorimeter, sold by Hach Co, for about $200. (To avoid this expense, you can also use a color chart for more approximate comparisons.) All the other items should cost less than $20. (Find more soil biology test kits under "Resources" at the end of this module.)