Comparing Variability of Soil Health Indicators to More Commonly-Measured Soil Nutrient Availability Tests.

Permanganate-oxidizable C (POXC), short-term mineralizable C, and soil protein are rapid and inexpensive soil health indicators that reflect soil biological activity and nutrient availability. However, how these indicators are repeatable in the laboratory, including their in-field spatial and temporal variability is not well-known. Our objective was to compare analytical, in-field spatial and seasonal variability of these indicators to the more commonly-measured soil nutrient availability tests. Soil samples were collected in a grid pattern at three time points over the corn growing season at three sites in Ohio, USA. We found mineralizable C to be the most analytically variable (coefficient of variation [CV], 13-23%), followed in decreasing order by total organic matter (loss-on-ignition) and POXC (CV, 6-13%), with soil protein, pH and macronutrients being the least analytically variable (CV <5%). Results from geostatistical analysis indicated that the vast majority of soil properties examined displayed moderate spatial autocorrelation and that soil nutrient tests showed spatial autocorrelation at shorter spatial ranges, suggesting that no additional soil samples may be required at higher densities for measuring soil protein and POXC than what is typically required for routine soil nutrient analysis. Our results also indicated that almost all soil properties examined varied within the crop growing season, underscoring the need for keeping a consistent time of year to soil sampling. In conclusion, soil protein and POXC are not more variable than most measures in a routine soil nutrient test, but that mineralizable C appeared to be more variable.