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Absolute values and precision of emerging soil health indicators as affected by soil sieve size

ABSTRACT Permanganate-oxidizable carbon (POXC), mineralizable carbon (C), and protein are rapid and inexpensive soil health indicators, which focus on the fast-cycling labile soil organic matter. We tested the effect of soil processing (sieve size) on measured values and analytical variability (i.e., precision) of each indicator. Soil samples were hand-sieved to < 8-mm, < 2-mm, or ground to pass through a 2-mm sieve. Mean values of POXC, protein and mineralizable C were higher in < 2-mm than in either ground or < 8-mm soils. Soils sieved to < 8-mm were significantly more likely than either < 2-mm or ground soils to result in higher analytical variability of POXC and protein, but sieve size did not affect the analytical variability of mineralizable C. These results collectively demonstrate that the use of larger size fractions like 8-mm sieved soils for measuring POXC and protein not only leads to lower absolute values, but also increases analytical variability and therefore minimize their precision.