Classify a pedon under the South African soil classification (1991)

Keys a PedonRecord to the soil forms of the South African soil classification of 1991 (Soil Classification Working Group, 1991; the "Blue Book"). Experimental: the book itself is not available to soilKey; the key is read from its open pages (the AGIS key and form pages, the general rules, the topsoil pages), SASRI (1999) and van Huyssteen (2020). It keys the 73 forms and, since v0.9.359, their 404 families.

Usage

classify_za1991(
  pedon,
  rules = NULL,
  on_missing = c("warn", "silent", "error"),
  gapfill = FALSE
)

Arguments

pedon

A PedonRecord.

rules

Optional pre-loaded rule set (load_rules("za1991")).

on_missing

One of "warn" (default), "silent", "error".

gapfill

Opt-in within-pedon gap-fill, as in classify_usda.

Value

A ClassificationResult with system_id "za1991": the form in rsg_or_order, the full name (form, family, texture) in name, the form and the family in levels (with name_en, soilKey's gloss of the form: the sequence of its horizons), the family read in qualifiers$za_family (its code and name, the partial code of an undecided family, the texture, and every criterion read: its class, the layers read, the stand-ins and the attributes missing), the sequence read in qualifiers$za_sequence and the identified layers in qualifiers$za_horizons (with za_truncated, za_land_class and za_nearest when they apply), the general rules applied, the stand-ins used and the nearest forms in warnings, and provisional_because.

Details

Each layer is read as one of the 30 diagnostic horizons and materials (see identify_horizons): from the name written in diagnostic_za (or in the designations of a profile declared with site$designation_system = "za"), else by soilKey's tests on the recorded data, three-valued, with WRB numbers standing in, flagged, where no open source gives the book's (the podzol B, the placic pan, the dorbank, the carbonate horizons and the colours of the subsoil). The profile is first read by the general rules: only horizons whose top lies above 1500 mm count; a recent deposit thinner than 500 mm over a buried soil is set aside and the buried soil classified, a thicker one is classified alone (recent_deposit, else its origin, flagged); a profile with no topsoil whose first horizon is a red or yellow-brown apedal B, a neocarbonate B, a dorbank or a hard plinthic B is read as truncated, an orthic A supplied.

A form holds when its horizons are the first of the profile's, in order (layers of no diagnostic horizon skipped), and the horizon that follows is not one that would make another form (Hutton over hard rock is Hutton; Hutton over a soft plinthic B is Bainsvlei). A description that stops above 1500 mm leaves the longer forms undecided, so the shorter one is provisional. When no form passes and some are undecided, the name lists them in the order of the key, provisional ("[Undecided in the South African soil classification (1991): Inanda ([Ia]), Arcadia (Ar), or not classified]", v0.9.402). The 500 mm rules of the form pages are tested too (Valsrivier, Sepane, Swartland, the podzol forms; Witbank, Dundee, Namib over a buried soil). A sequence no form has gives no form, with the nearest forms in the warnings; an orthic A under 100 mm thick over nothing diagnostic is the land class "rock and lithosols" (general rules). Lichtenburg (orthic A, red apedal B, hard plinthic B) is named by van Huyssteen (2020) but not by the AGIS key of 1991: it is keyed, always provisional. The readings soilKey makes where the open sources are silent are in system.file("rules", "za1991", "readings.yaml", package = "soilKey").

The families (v0.9.359) are read by the 19 family criteria of the book, each on the horizon its family names (the B1 of the red apedal B, the E, the upper G, the layer under the placic pan ...), as the form key identified it: the first family whose classes all hold is the family; with a criterion undecided for lack of data, the result names the families left possible and soilKey's partial code, an "x" for each undecided digit ("Hutton, [Hu1x00]"). The name follows the identification of the book: the form, the family code and name, and the USDA texture class of the A when its clay, silt and sand are recorded (with the sand grade of sand_grade): "Hutton, Hu1200 Kelvin, sandy loam".

References

Soil Classification Working Group (1991). Soil classification: a taxonomic system for South Africa. Memoirs on the Agricultural Natural Resources of South Africa No. 15. Department of Agricultural Development, Pretoria.

See also

make_za1991_example, identify_horizons, soilkey_systems.

Examples

res <- classify_za1991(make_za1991_example("hutton"), on_missing = "silent")
res$name
#> [1] "Hutton, Hu1100 Lillieburn, sandy loam"
res$qualifiers$za_sequence
#> [1] "OA - RAB"