Soil (health) evaluation begins by asking “What’s the problem with my soil?”
Posted by Andrew McGuire | July 9, 2019
Soil health – the pursuit that launched a thousand soil tests. I have not counted them, but many people are working on many ways to evaluate soil health. Some are looking at indicators of soil biology status, others at the soil’s physical state, many at various measurements of soil organic matter. There are lists of tiers of tests: the USDA’s Natural Resource Conservation Service has a list, the Soil Health Institute has a list, with tiers, and the soils lab at Oregon State University has a list. The lists are similar, but not identical. Commercial labs are joining the effort offering various tests: Solvia, the Haney test, fungal:bacterial ratios, and more. The lists will get pared down and labs will figure out the most relevant tests for their clientele, but before you take any soil samples, before you have any samples analyzed, before you start worrying about your soil biology, ask yourself, “what’s the problem with my soil?”
The problem with lab-based soil health evaluation is that it is not focused on one problem, on your problem. Often it is assumed that you don’t have soil health and that you need to get it, but the lack of soil health is not a real problem. Nor is your problem low active carbon, soil respiration, or microbial biomass. Those soil health indicators may or may not correlate with the actual problems you have with your soil…if you have a problem. And that is the place to start, determining if you have a real problem with your soil, and if you do, what exactly is it? Start by asking: what is your soil doing that you don’t want it to do, or what should it be doing that it’s not?
Problem-based soil evaluation
Here is a series of questions to start your problem-based soil evaluation. Originally from Caley Gasch, soil scientist with North Dakota State University, I have modified them a bit, putting the problems in order from higher to lower in terms of the problem’s long-term consequences, harmful effects, and responsiveness to management.
What we want is for the soil to function in a way that enhances the main goal of agriculture: to produce food, and to keep on producing food. Function here has to do with air, water, and nutrients.
Erosion is first. If you have erosion, water or wind, fix it first. It makes no sense to be worried about soil biology, mycorrhizae, soil regeneration, or the soil food web if your soil is leaving your farm. The good news is that many of the fixes for soil erosion – increased residues on the soil surface, reduced tillage, cover crops – also benefit other aspects of soil health.
Next is how your soil handles water at the surface, infiltration, and below the surface, drainage. Then surface crusting, nutrient cycling and finally soilborne pests and diseases.
If you go down the list and your answer to the last question is “yes” then you must determine the most likely reason for your crop’s problems. This is where a shovel can help and if needed, a diagnostic lab. Is it soilborne disease, insects, salinity, etc.?
This list covers the most common problems but not all of them. Some of the problems may be related to each other. If they are, determine what they have in common. For instance, poor infiltration and wind erosion may be related to the lack of soil structure which is related to the low amount of soil organic matter. Why is there low soil organic matter? Low residue crops, too much tillage, plowing the surface organic matter into deeper layers? Keep asking why until you come to the root problem. This often comes back to soil organic matter and its management, but not always. Even if you have figured out that higher organic matter is the solution, you know WHY this is the problem and what other problems are related to it. This is an improvement on just building soil organic matter for the nebulous goals of soil health or soil biology.
Now that you have identified the root problem you can attack the problem directly rather than through “soil biology” or some similarly vague tool. This problem-based soil evaluation will quickly focus your attention on the actual functions of your soil. It bypasses the fuzzy idea of achieving “soil health” and identifies something to guide your management decisions. It grounds your actions on solving a problem. Then it is much easier to decide what to do first and how to evaluate your progress.
What about soil health testing?
Having identified your problems, you can proceed with management and with soil health testing. “Test your soil” is a long-time mantra of Agricultural Extension, because, as the saying goes, you cannot manage what you don’t measure. But like testing your soil’s nutrient levels and then making decisions based on your planned crop, you can conduct soil health testing with a certain problem in mind. Perhaps there are tests that are associated with your problem more than others. Use those to evaluate your plan to address the problem.
Perhaps this is all just common sense, but common sense is needed here. This method is specific, practical, and immediately useful. It drives solutions that solve the problem in a way that soil testing by itself cannot. What if you don’t identify any problems or if you solve them? Do you then have a healthy soil? I think that, as with a healthy person, a healthy soil should not be expected to be completely free of problems – a healthy person is still susceptible to colds, or the flu – but overall a healthy soil will have fewer problems than an unhealthy one, and be able to overcome those problems that do occur.