Soil Health Analysis, Set. Группа авторов
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we want to conduct the measurement”? A third important limitation involves the number of management changes that are needed to fully execute a comprehensive soil health management approach.
Phosphorus loss from agricultural fields provides an excellent example of this third limitation. Growing cover crops and reducing tillage are often promoted as soil health improving practices because of their impact on SOC, but they may not be sufficient to reduce P losses from agricultural fields. Since either high soil‐test P levels, excessive P applications through fertilizer or animal manure, or high soluble P in senescing cover crop vegetation can all contribute to increased soluble P runoff, soil health management practices focused on this problem must be coupled with changes in the way P is applied to the fields. This could easily involve new materials, timing of application, and/or equipment (Duncan et al., 2019). Therefore, an effective soil health research project may require substantial changes to all dynamic soil properties and associated management practices, which from a practical perspective can be a limitation when multiple fields and/or producers are involved.
Other potential limitations to useful soil health research and technology transfer include factors such as producer interest, economic limitations, time requirements, and the magnitude of change needed with regard to soil and crop management practices and/or desired with regard to soil properties. The utility, however, is emphasized by the numerous potential endpoints that exist, especially when balancing productivity with a broader environmental perspective. Is the ultimate endpoint of improved soil health increased yield, long‐term sustainability, water quality, economic viability, community development, or all of these goals? The length of time for which soil health indicators must be tracked and whether or not changes can be documented will be determined by the ultimate goal(s). This also determines the magnitude and type of change that must be measured. Without any doubt, research studies can document findings that are both statistically significant and practically important. However, depending on (1) how changes are measured, such as with an in‐field test, commercial, or research laboratory test, (2) the inherent soil variability and (3) the analytical soil test variability, one or more of those factors can potentially mask any true soil health effects. It is not surprising, therefore, that all of these challenges (i.e., endpoints, time, magnitude of change) reflect various trade‐offs. Research projects tend to be funded for relatively short periods of time, often measured in two to five year increments, research budgets are not unlimited, and every sample that needs to be analyzed requires careful collection, appropriate preparation and adequate processing time. Obviously, these challenges are not unique to soil health research, but recognizing them may help diffuse some of the discussion between those who view the efforts as either useful or futile.
Conclusions
Documenting benefits from soil health approaches first requires defining what is the benefit of interest and then selecting ways to measure and document the response. The principles associated with soil health are not new as evident by centuries of soil management, conservation, condition, tilth, quality, and other terms. Among the well‐known and generally accepted approaches for improving soil health are the goals of keeping the soil covered, reducing disturbance, maintaining plants year‐round, and diversifying the mix of plant species. Implementing these goals can increase the quantity of plant residues and root exudates returned to the soil, boost microbial activity, and ultimately lead to a cascade of soil improvements, including increased SOM, more stable soil aggregation, and efficient nutrient cycling. How well these benefits can be documented depends on the magnitude of change (generally determined by inherent soil properties and/or initial conditions) as well as the type of soil health test selected (i.e., in‐field, commercial or research laboratory, remote sensing), and the scale at which comparisons are to be made and meaningful (i.e., from landscapes down to finely sieved and crushed soil samples). Interactions between inherent and dynamic soil properties can also make documenting soil health benefits difficult, since spatial and temporal variability can mask potential changes associated with new soil and crop management practices, such as annual cover crop establishment, which must be given adequate time for measurable effects to occur. Extreme weather conditions, such as too much or too little rainfall, early or late frost, or above normal temperatures can hinder the effectiveness of new or alternative management systems and prevent them from becoming established and changing soil properties in subsequent years. Without question, researchers have documented numerous benefits from soil health approaches. As the concept evolves, the core questions of defining what constitutes an important benefit and selecting reproducible methods to measure that benefit will remain a constant challenge and an important research goal.
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