To have robust soil health your soil must first meet certain criteria for microbial activity. You can be a marathoner but your exercise regime, rest schedule and nutrition has to be right to succeed. The same applies to microbial activity. The home of microbes is the soil environment which must be suitable for them to flourish. And the quality of specific components determines the integrity of this house.
Discussions about soil quality were very controversial in the 1990s because academics didn’t feel it was definable. In 2014 I wrote an article on soil quality for Crops and Soil magazine and received a comment from an emeritus professor that “quality isn’t definable”. For me, an agronomist and farmer, it is definable and measurable. I take a very practical view, and the NRCS seems to agree.
The NCRS has been interested in soil quality and in providing training for over 2 decades. I have even been through this training in Nebraska and it taught me how to easily measure and track quality. The NRCS’s Soil Quality Institute published their Soil Quality Test Kit Guide in 2001. In it they define soil quality as “the capacity of a specific kind of soil to function. It is generally assessed by measuring a minimum data set of soil properties to evaluate the soil’s ability to perform basic functions (i.e., maintaining productivity, regulating and partitioning of water and solute flow, filtering and buffering against pollutants, and storing and cycling nutrients).”
The kit and methodology was developed by Dr. John Doran, USDA ARS scientist at University of Nebraska. Cathy Seybold and Lee Norfleet, USDA-NRCS wrote the guide. It describes indicators of soil quality – or the integrity of the home. However, don’t forget to use a spade and dig up a slice of a soil profile and get your hands dirty. Remember seeing, feeling and smelling the soil is part of monitoring quality. A crumbly dark soil with a good earthy smell and worms is what you desire and we don’t have lab measurements to tell you that.
Measuring soil physical qualities can be time-consuming because you have to do the tests yourself. It is also best done in the field in a natural, undisturbed state. Physical quality includes bulk density, porosity, water holding capacity, water infiltration, presence of compaction layers, and aggregate stability. The NRCS’s Soil Quality Test Kit explains how to run these tests. The equipment that is part of the kit is largely re-usable and once assembled the only real expense is the time it takes to do the tests.
Soil quality assessments include a long list and I have made a short list: organic matter, pH, EC, aggregate stability, compaction and water infiltration. This doesn’t yet tell me anything about biology. To measure that, I add in the Solvita field respiration test. The original NRCS Soil Quality kit included a glass-absorption tube called Draeger to measure soil CO2, and John Doran and his team at UNE showed already in 1997 that Solvita was easy and accurate to perform. Check out the Soil Bucket for all these short list of tests. I like the infiltration ring – which also serves for bulk density tests, and I’d throw in a penetrometer, which the NRCS bucket does not include and that helps you get to soil compaction.
Once I understand my soil quality and have taken necessary steps to maintain and improve it, I feel that a routine Solvita field respiration test is all I need to keep monitoring it. If respiration falls off, then I look at other indicators to find the causes. If you are monitoring soil quality, or soil health as we know it today, the traits measured in NRCS’s Kit are ones that determine the dynamic nature of your soil. You won’t know if your soil is in good shape if you don’t measure. So let’s get out and do it.
You can send a question, comment or topic to our guest blogger Dan Davidson CCA at: ddavidson @ woodsend.com. Dan also accepts calls at 402-649-5919.