AOAC SPADA Meeting

Soil horizons:  •Consist of the O, A, E, B and C horizon •Not all horizons are present in a soil •Each horizon has different properties •The soil horizons and their properties identify  the soil •Soil on top of another soil is possible, usually  due to flooding

The 12 Soil Orders

• Entisol – Youthful soil with little profile development • Andisol – Not a well developed clay layer but prominent organic‐rich A  • Gelisol – Permafrost within 1 m of soil surface • Histosol – Organic accumulation of great depth due to anaerobic conditions • Inceptisol – More well developed clay layer or B horizon • Aridisol – Arid to semi‐arid ecosystems of shrub and short grasses • Vertisol – Highly‐active and swelling clay  • Mollisol – Semi‐arid or moist grassland ecosystem and deep organic‐rich A • Alfisol – Clayey B horizon with low acidity • Spodosol – Humic B horizon with high acidity and coarse texture (sandy)

• Ultisol – Clayey B horizon with high acidity • Oxisol – Oxic B hoizon with low‐activity clay