Soil storage changes enzyme activity magnitudes but preserves activity sensitivity to long-term crop rotations and tillage practices

Abstract Soil samples are often stored prior to enzyme activity assays, but storage-induced changes could compromise the ability to differentiate activities among management practices. We used two field experiments in north-central USA – 27 y crop rotation × tillage on an Endoaquoll-Argiudoll and 53 y tillage on an Endoaqualf – to quantify the effects of storage by refrigeration (4 °C), freezing (-20 °C) and air-drying (≈ 24 °C) over 24 mo on activities and sensitivity of activities to field treatments relative to field-fresh soils (≤ 3 d at 4 °C) for β-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG), acid phosphomonoesterase (acid PME), alkaline PME, and arylsulfatase (SUL). Storage effects and in particular storage duration generally exceeded field treatment effects on activities. Depending on the enzyme, activities fluctuated irregularly across storage duration from + 220% to -90% relative to field-fresh soils. Sensitivity of enzyme activity to field treatments increased or decreased irregularly across duration on both Endoaquoll-Argiudoll and Endoaqualf compared to field-fresh soils. Higher NAG activity under maize-maize than soybean-soybean was well preserved in frozen and air-dried soils, and to some extent in refrigerated soils. Higher SUL activity under no‑tillage than chisel tillage on the Endoaquoll-Argiudoll was preserved across all storage methods. In the Endoaqualf, differentiation between no-tillage and moldboard tillage by BG, NAG, acid PME, and SUL activities was maintained in stored soils. Despite substantial changes in activities and sensitivity to field treatments, storing soils by refrigeration, freezing, or air‑drying for up to 24 mo preserves the ability to distinguish activities among contrasting crop rotation and tillage in representative soil types of north-central USA.