Rethinking soil precompression stress: Separating resistance, mechanical yield and functional limitation

Precompression stress is widely used to assess soil load-bearing capacity, yet its physical threshold meaning remains uncertain. Resistance, mechanical yield and functional limitation are related but distinct. Breakpoint regression is treated here only as an operational estimator of mechanical yield when the observed stress-strain curve supports two local regimes; curve shape, stress scale, test protocol and breakpoint uncertainty must be declared. A function-specific limiting stress is then defined as the applied stress at which a selected soil capacity crosses a process- or management-based limit. The difference between this limit and the mechanical breakpoint—the mechanical-functional gap—shows whether hydraulic, aeration, microbial or root-related capacity becomes limiting before or after mechanical yielding, while its confidence interval determines whether the ordering is distinguishable from zero. Water status, drainage, loading history and recovery make both quantities protocol- and time-dependent. Existing function-based limit systems are complemented, not replaced. A synthetic illustration and an experimental workflow show how the two stress estimates and their gap can be quantified for field traffic and tillage management.