How to Design Evaluations

The most practical use of existing assessment tools is to compare the effects of management practices on soils to help adapt practices to better meet management goals (e.g., yield, environmental protection, reduced erosion, etc.).

It is important to understand that most every dynamic soil property varies (often widely) by soil type and this typically is much greater than the differences induced by land management. Consequently, except for traditional nutrient soils tests, most soil quality indicators by themselves are not calibrated. Thus, it is necessary to have some sort of spatial or temporal comparison on the same soil type.

To compare soil quality one can measure indicators over time at one site. Another acceptable use is to compare practices at adjacent sites, if care is taken to account for the inherent soil differences between the sites. As indicator interpretation is improved, it should be possible to make comparisons across sites by measuring the same indicators at each site.

The properties observed in a high quality soil will vary from place to place, depending on parent soil type and management history, as well as the agricultural production system and environmental context. Given this variability, it is quite useful to find a ‘benchmark’ soil near each field site. This could be a fence row or nearby area of natural vegetation, where the soil is in a relatively undisturbed and high quality state. Once this benchmark is identified, soil properties can be measured at the benchmark and the field sites of interest. The ‘high quality’ benchmark soil will ideally provide a goal post: the optimum soil properties possible at that site given the parent soil type and local environmental conditions.

It is important to carry out soil quality monitoring observations over time. Many properties vary depending on the most recent field operation and require observation over a season, and ideally over several years. A general increase in soil quality characteristics is the goal, with an upward trend towards the soil quality observed at the bench mark site.

The tools available on this web site can be used to:

compare 1 practice, 1 site, over time
compare multiple practices, 1 site (adjacent sites), 1 time or over time
compare 1 practice, multiple sites (this is the least reliable)