Repeatability and Spatiotemporal Variability of Emerging Soil Health Indicators Relative to Routine Soil Nutrient Tests

Abstract

Core Ideas POXC, mineralizable‐C, and protein are emerging soil health indicators. POXC and mineralizable‐C have analytical variability similar to OM via loss‐on‐ignition. Soil protein has smaller analytical variability similar to Mehlich‐3 extractable nutrients. Soil health indicators exhibit spatiotemporal variability to a similar extent as routine nutrient tests. Soil health indicators do not require greater soil sampling densities within a field. Ideal indicators suitable for routine soil health evaluation would be rapid, cost‐effective, sensitive to management, and exhibit low analytical variability. Permanganate‐oxidizable C (POXC), mineralizable C, and soil protein are rapid and emerging soil health indicators of labile organic matter (OM), but their repeatability and spatiotemporal variability remain largely unknown. We examined the repeatability and spatiotemporal variability of each indicator relative to routine soil nutrient tests. Grid soil samples were collected three times during a corn (Zea mays L.) growing season at three sites in Ohio. Analytical variability of indicators ranked from highest to lowest mean coefficients of variation (CVs): mineralizable C (13–23%) > OM via loss‐on‐ignition (OM‐LOI; 11–16%) = POXC (9–19%) > protein (2.6–3.2%) = Mehlich‐3 P (1.8–2.6%) = Mehlich‐3 K (3.0–3.8%) > pH (≤1%). Temporal variability of indicators ranked from highest to lowest mean CVs: mineralizable C (22–37%) > OM‐LOI (16–25%) = POXC (9–21%) = Mehlich‐3 P (14–33%) = Mehlich‐3 K (6–33%) ≥ protein (7–13%) > pH (1.7–3.6%). Almost all soil properties exhibited moderate to strong spatial autocorrelations, occurring at range distances ≤76 m. Our results collectively suggest: (i) mineralizable C and POXC have analytical variability similar to that of OM‐LOI, whereas soil protein similar to Mehlich‐3 extractable nutrients; (ii) the soil health indicators exhibit temporal variability to a degree similar to routine soil nutrient tests; and (iii) the soil health indicators display spatial variability to a similar extent as the routine soil nutrient tests and therefore do not require greater soil sampling densities within a field.