Aubrey K. Fine, Aaron Ristow, Robert Schindelbeck and Harold van Es
Soil and Crop Sciences Section, School of Integrative Plant Science, Cornell University
Comprehensive Assessment of Soil Health
Soil health refers to the ability of a soil to function and provide valuable ecosystem services. The Comprehensive Assessment of Soil Health (CASH) is a testing approach developed at Cornell University that measures multiple physical, biological, and chemical soil properties linked to key soil processes (Table 1). It remains largely unclear how soil health varies in different agro-ecological regions, and whether interpretation schemes should therefore be adjusted. As a preliminary investigation into these questions, we used the CASH sample database to compare the soil health status of 5,767 samples collected from the Mid-Atlantic, Midwest, and Northeast regions of the United States.
Database Analysis
CASH uses scoring functions that are developed using the cumulative normal distribution (CND) of measured values in our database for each indicator. Scoring functions for physical and biological CASH indicators are calculated using the CND, whereas chemical indicators are scored based on experimentally-established thresholds. Some, but not all, indicators showed texture-dependence; in these cases, separate scoring functions for coarse, medium, and fine textures were developed. The scoring function allows for the interpretation of the measured value for each indicator on a scale ranging from 0 to 100. This approach lets us assess how a particular soil sample scores relative to other similarly-textured soil samples in our records, and thereby make some judgment on the relative health of that soil to identify possible problems.
Since it began offering soil health testing services in 2006, the Cornell Soil Health Lab (CSHL) sample database has grown considerably in size and geographic scope. After evaluating the number of samples analyzed from each of the 48 continental United States, we identified three regions having sufficient sample size (n=5,676 total) including the Mid-Atlantic, Midwest, and Northeast. These regions align with the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Major Land Resource Areas (MLRA) (Fig. 1). Descriptive statistics and ANOVAs of sub-datasets by region and soil textural class for all CASH indicators were performed, allowing comparisons among these three regions in measured values of soil health indicators. The medium textural group made up the largest proportion of our database, and for brevity we only report this textural group results here (Table 2). A manuscript that also includes results of fine and coarse textural groups is in preparation for publication by Fine et al. (2017).
Results
With this investigation, we observed significant regional differences in mean measured values for most physical, biological and chemical indicators (Table 2).
For medium-textured soils, significant differences between regions were observed for most indicators except subsurface compaction (PR45) and extractable potassium. In general, soil health values for the Midwest region were less favorable compared to the Mid-Atlantic and Northeast, notably for Wet Aggregate Stability, Organic Matter, Active Carbon, Protein, Respiration, and Root Health. Extractable phosphorus levels were notably higher in the Mid-Atlantic region. Although sample sizes between regions were unequal, Midwestern soils generally showed lower variability (standard deviations) in measured values.
These results offer insights into regional soil health differences that can be attributed to genetic and management factors. The lower mean values observed for biological indicators and Wet Aggregate Stability in Midwest soils counter the common notion that Midwestern soils are of superior quality than those in other regions. How can this be explained? First, there are likely differences in cropping systems. Northeast and Mid-Atlantic soils generally receive more organic inputs (especially manure) and are often managed to include diverse rotations with perennial crops, as opposed to typical corn-soybean rotations in the Midwest. Second, the standard CASH is limited to the 0-to-6 inch depth interval, and, therefore, the deeper soils and organic matter accumulation in many fertile Midwestern prairie soils is not captured by the test. Finally, these findings could suggest an inherent bias in our data set, so conclusions should be interpreted with some caution.
Conclusion
What have we learned? An investigation into regional soil health status (Mid-Atlantic, Midwest, and Northeast) showed significant differences in mean measured values for most physical, biological, and chemical indicators. Evidence suggests that the development of region-specific scoring functions may be appropriate, but would require more complete regional soil health data collection and analysis. In all, this project provided valuable insights into the soil health status of three different agro-ecological environments. We conclude that the CASH approach can be successfully applied to evaluate the health status of soils of differing agro-ecological environments, but that interpretations likely need to be regionally adapted to be most meaningful.
For more details about the CASH framework, visit bit.ly/SoilHealthTrainingManual for a free download of the third edition of the training manual.
Reference
Fine, A.K., van Es, H.M., and R. R. Schindelbeck. 2017. Statistics, Scoring Functions and Regional Analysis of a Comprehensive Soil Health Database. Soil Science Soc. Am. J. (in preparation).
