The USDA oxic horizon is the diagnostic of Oxisols. Its central criteria match the WRB 2022 ferralic horizon closely enough that v0.2 simply delegates: every fixture that classifies as Oxisol via USDA also classifies as Ferralsol via WRB and vice-versa. The fine-grained differences (USDA's water-dispersible-clay test, the sand-fraction weatherable-mineral cut-offs) are tracked in the diagnostics.yaml for v0.8 refinement.
Arguments
- pedon
A
PedonRecord.- ...
Passed to
ferralic.
Value
A DiagnosticResult (with name = "oxic_usda").
Details
The CEC limit is inclusive here: KST 13 (Ch. 3, oxic horizon, criterion
6) asks for "an apparent CEC of 16 cmol(+) or less per kg clay", where WRB
2022's ferralic horizon asks for "< 16". Since v0.9.212 ferralic()
follows WRB and this function passes cec_inclusive = TRUE, so a
horizon at exactly 16 is oxic but not ferralic.