Soil Health Analysis, Set. Группа авторов

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. This is precisely the situation experienced by VeVerka et al. (2019) in a study of Missouri claypan soils across four watersheds for 3 yr. They were able to detect expected depth differences in soil properties, with surface samples having greater soil biological activity, as indicated by higher enzyme and organic matter values. However, this trend did not occur for glucosaminidase, since quantities of that enzyme actually increased with depth. Overall, the expected soil health indicator improvement expected for no‐till plus cover crops in comparison to tilled, no cover crop treatments did not occur presumably because of unfavorable growing conditions.

      Another common short‐term soil health evaluation is to compare two widely varying production systems from opposite ends of a disturbance continuum (e.g., perennial grassland vs. a tilled field). Transitioning from grassland to a tilled field typically causes shifts in soil biological activities, sometimes within the first month after tillage commences. In Texas, Cotton and Acosta‐Martínez (2018) documented a 52% decrease (505 to 241 mg kg⁻¹ soil) in soil microbial biomass in the top 10 cm of the soil profile. After the first growing season, soil organic carbon (SOC) within the top 30 cm of the profile declined by an average of 20%, although the decline in the surface 10 cm (11.60 vs. 7.28 g SOC kg⁻¹ soil) was substantially greater than within the 10‐ to 30‐cm increment (6.76 vs. 6.17 g SOC kg⁻¹ soil). This was not unexpected since in most soil health studies, soil property changes are greater near the soil surface because this portion of the profile is most directly affected by changes in tillage and plant root conditions.

Soil management practices that increase microbial food supplies and reduce disturbance to their habitats will tend to have greater soil microbial activity than soils with limited food sources (i.e., SOC), due to low crop residue or root carbon inputs, excessive crop residue removal, or excessive tillage. Sustaining adequate soil microbial activity is important because biologically mediated processes such as nutrient cycling and SOM dynamics are critical components of several soil ecological functions (Dick, 1992). For example, in comparisons between conservation reserve program (CRP) fields and active croplands, Li et al. (2018) found that fungal abundance increased in proportion to the length of time since CRP practices were implemented. They found increases in fungal abundance up to 15 yr after establishment, followed by decreases relative to bacterial abundance. The shifts in microbial community composition were attributed to historical soil conditions, abiotic factors and climate properties. Soils in CRP had less stressed soil microbial communities as indicated by fatty‐acid methyl ester biomarker (FAME) profiles, in which the ratio of saturated to mono‐unsaturated fatty‐acids decreased (Li et al., 2018). The mono‐unsaturated fatty‐acids indicated active metabolic processes were occurring in the soil compared to higher saturated fatty‐acid profiles that are indicative of slower metabolic processes which can occur when water or nutrients are in short supply for microbes.

Soil Health Limitations

      There are at least three related components that can limit the utility of soil health research and implementation efforts. First are the logistical limitations including the cost of a project, access to samples or instrumentation, and time for the study to be conducted. Next, are the philosophical limitations that can occur when an assessment project is designed, especially regarding the scope and questions of interest. These types of limitations generally occur if someone considers the project’s approach to be insufficient to answer what is often potentially a broader or different question. Logistical and philosophical limitations do overlap. For example, consider