The concept of field capacity revisited: Defining intrinsic static and dynamic criteria for soil internal drainage dynamics

Across many soil types and conditions, post wetting soil internal drainage exhibits predictable dynamics that lead to a stable and repeatable hydration state termed “field capacity” ( FC ). Soil regulation of internal drainage toward FC has long been recognized as producing a useful hydrologic benchmark for modeling and for estimation of plant available soil water. To overcome ambiguities and inconsistencies in various ad hoc definitions of FC , we propose using a soil intrinsic characteristic length (a matric potential value derived from drainable soil pore size distribution) to characterize the loss of hydraulic continuity associated with the attainment of FC . The resulting static criterion for FC was extended to formulate a self‐consistent dynamic criterion based on soil internal drainage dynamics. A systematic evaluation of the proposed definitions of FC using numerical simulations and experimental data reveals remarkable consistency and predictability across a wide range of soil types. The new metrics add definitiveness and robustness of this widely used concept with potential expansion to additional agronomic, hydrologic, ecological, and climatic applications.