Have you checked the health of your soil lately? Checking respiration of your soil is like checking your pulse—indicating your health level, but not what may be impeding or stimulating it.
Checking the health of your soil is easy. You probably are checking a few things already and don’t know it. When you run a soil test and measure pH and organic matter you know some of the elements that contribute to soil health.
Soil health is determined by chemical, physical and biological properties.
Some of the most common chemical soil indicators are organic matter, pH, salinity and electroconductivity (EC). A soil laboratory can run these tests.
Some common physical tests are porosity, bulk density, water infiltration and aggregate stability. Unfortunately, these must be done in the field, either by you or someone you hire. Field kits can be assembled to measure these physical indicators, but tests are a bit tedious. If the soil is impeded physically, you can’t optimize biology.
Fortunately, a laboratory can measure the biological health of your soil using multiple methods. One of the most well-known measurements is the Soil Health Test being promoted by the Natural Resources Conservation Service (NRCS). The less-known Haney Test, developed by Rick Haney, USDA scientist at Texas A&M University, looks at soil respiration and carbon and nutrient cycling. It may be done by several laboratories approved by the NRCS.
Additional tests include the Cornell soil health test, active carbon (permanganate carbon test), mineralizable nitrogen (ISNT, SLAN), microbial diversity (PLFA) and soil aggregate stability (VAST, SLAKE). You can find laboratories that do all or some of these tests.
At the end of the day I like to measure six things:
- Organic matter
- Active carbon
- Nitrogen mineralization
- Aggregate stability
I consider these to be some of the more important indicators out of the 12 or 15 possible tests. And these listed can be done by a commercial soil laboratory.
However, at the top of my list is measuring soil respiration because all the factors that influence soil health also affect respiration. This one test aggregates all influencing factors into a single measurement. This is like measuring your pulse, where a lot of things about your blood chemistry, health and lifestyle affect this single measurement. We know if a person’s pulse is too low or too high something is wrong. It’s the same with soil respiration.
Soil respiration can be measured by the 24-hour CO2 burst test or by 3-day or 7-day respiration tests. The longer runs are generally not popular with commercial laboratories because of time and cost. The Solvita® CO2 burst test can record bursts of 30, 60, 90 or 120 ppm or more in 24 hours. Obviously, the higher the value the more active the soil’s microbial pool. Remember, microbes actively feed on carbon and recycle nutrients to feed roots and humic compounds to improve the soil. And the bigger the burst the larger the pulse.
For additional perspectives read “Food Security from the Soil”, an interview with Anthony Bly, Extension soils field specialist at South Dakota State University, published in the March/April 2017 edition of the South Dakota Soybean Leader magazine.
Soybean agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at firstname.lastname@example.org or ring him at 402-649-5919.