Figure 3.4 Potential scales at which soil health indicators can be assessed.
(Photo credit: Gary Radke, USDA ARS).
Two important realities of soil health assessment, regardless of the specific test being used, are the recognition and improved understanding of soil function. Having that knowledge enables NRCS and other consultants to help producers evaluate several soil‐related natural resource concerns (Table 3.4) and to recognize that although any of the three types of soil health tests could be used, some may be more useful for determining if a specific concern is present and subsequently how to address it. Therefore, it is important to recognize that the assignments we list in Table 3.4 simply represent common measurements and that other tests could easily be used.
Table 3.4 Potential soil health tests for evaluating various natural resource concerns.
| Natural resource concern | Most common type of soil health assessment | ||
|---|---|---|---|
| In‐field | Commercial lab | Research lab | |
| Erosion | ✓ | ||
| SOM depletion | ✓ | ✓ | ✓ |
| Elevated salts | ✓ | ✓ | ✓ |
| Excess water | ✓ | ||
| Insufficient water | ✓ | ||
| Pesticide transport | ✓ | ✓ | |
| Excess pathogens | ✓ | ✓ | ✓ |
| Heavy metals | ✓ | ✓ | |
| Sediment in surface waters | ✓ | ✓ | ✓ |
| Elevated water temperatures | ✓ | ||
| Degraded plant condition | ✓ | ||
| Wildfire hazard | ✓ | ||
| Odors | ✓ |
It is also important to recognize that each type of soil health test will have variability associated with the end result. Furthermore, documenting changes in soil properties is also challenging by the fact that soils are inherently variable. A test with high variability may complicate its use to quantify changes due to management simply because any true changes become lost within the larger variability of the test itself. Selecting the appropriate type of test and scale at which to use it is therefore an ongoing question in soil science. Thus as land management practices change, soil health measurements may also have to change to detect subtle changes in soil properties or functions.
The living, dynamic nature of soil resources contributes to what some consider the futility of soil health assessment. For example, depending on site‐specific field properties, the number of soil samples required for a meaningful soil health measurement can vary widely (Cambardella et al., 1994; Hurisso et al., 2018; Ladoni et al., 2015; Morrow et al., 2016; Necpálová et al., 2014). Also, although there are several types of qualitative and quantitative tests that can be used to analyze soil health properties, the decision on which approach to use will ultimately depend on the type of questions that are to be addressed. For example, sediment in surface waters can be detected using in‐field techniques by simply noting the presence of soil particles in water being collected as run‐off from a specific area. These in‐field tests could be made more quantitative by documenting the amount of sediment per unit volume of water if a known volume is collected, the water is evaporated, and the remaining amount of sediment is weighed. However, if the goal is to determine the concentration of a specific element or chemical in the run‐off water, the surface water samples that are being collected will have to be sent to a commercial or research laboratory where analytical tests beyond the scope of an in‐field test can be made. Or, substantial in‐field or edge‐of‐field instrumentation will need to be installed to quantify these concentrations.
Degrees of Change
Opinions regarding the utility or futility of soil health assessment are often based on the challenges of documenting benefits from soil health approaches which are highly dependent on the question of interest, type of test used, and scale at which the test is applied. We advocate that to be considered soil health research, assessments must include soil physical, chemical, and biological properties, although some would argue that focusing on one particular soil property is sufficient. We consider that latter approach to be soil physical, soil chemical, or soil biological health and not soil health per se.
Other chapters in this book provide a more thorough discussion and specific information regarding individual soil health assessment methods. The examples included herein are simply intended to be illustrative of how soil health benefits have been documented in the scientific literature. Our goal is to highlight the types of soil system comparisons that have been made, including those examining different types of cropping systems, large scale changes associated with a disturbance continuum, and subtle changes in soil properties over time. Obviously, these are not the only types of comparisons within the soil health literature, but they were selected to illustrate the types of challenges associated with documenting soil health benefits.
Soils managed using no‐tillage with the addition of cover crops are expected to have better soil health properties than tilled soils without cover crops because the former results in greater SOM, higher soil enzyme activities, and more stable soil aggregation. Furthermore, soils managed under no‐till with cover crops fulfill many of the goals from Table 3.2, including maintaining soil cover, reducing soil disturbance, extending the time when vegetation is growing for as long as possible, and diversifying plant species across the landscape. However, these potential soil health benefits are not guaranteed. If cover crop establishment is poor for several consecutive years because of weather patterns (e.g., unusually early freezing or substantial drought conditions), the magnitude of soil change could be quite limited.
