New Zealand Soil Classification (NZSC)

Horizon notations and diagnostic characteristics

Selected horizon notations and related diagnostic horizons of the NZSC

Definitions of the diagnostic horizons or diagnostic features are more restrictive than definitions of horizon notations (for example, thickness limits are imposed on many diagnostic horizons). The relationships shown here are therefore only approximate. Complete lists and definitions of soil horizon notations are given in Milne et al. (1995), and diagnostic horizons, soil materials and soil features are given in Hewitt (2010).

Horizon NotationDefinitionRelated diagnostic horizon or feature
O Organic material, accumulated under wet conditions Peaty topsoil, organic soil material
A Mineral horizon (topsoil) formed at the soil surface characterised by incorporation of humified organic matter  
Ah Topsoil undisturbed by ploughing Distinct topsoil
Ap Topsoil disturbed by ploughing Distinct topsoil
E Horizon below the H, O, or A horizon that has lost clay, iron or aluminium (eluviated) leaving it relatively pale  
A/B Zone of mixing between A and B horizons, frequently caused by worms  
B A mineral horizon that has been altered by the formation of soil structure, brighter colours (than horizons above or below), or by enrichment in mineral or organic material  
Bw B horizon, altered by weathering, evidenced by contrast in colour or structure Weathered-B horizon
Bt B horizon enriched in clay Argillic horizon
Bh Dark B horizon enriched in humus Podzolic-B horizon
Bs B horizon enriched in oxides of iron, aluminium with humus Podzolic-B horizon
Bo B horizon enriched in kaolin-group clays with iron and aluminium oxides Oxidic horizon
Bg B horizon with mottled grey and yellow/orange colours indicative of reduction (gleying) Mottled profile form, gley profile form, perch-gley features
Br B horizon with strong reduction due to intense gleying and predominant grey colours. Gley profile form, perch-gley features
Bk B horizon enriched in calcium carbonate Calcareous horizon
BC Transitional between B and C horizons  
BCx BC horizon that is compact but not cemented Fragipan
C Underlying unconsolidated material, usually showing some weathering but minimal biological activity  
R Underlying bedrock Lithic contact