the (mainly climate-controlled) distribution of kauri (Agathis
australis). Limited areas of Ultic Soils occur in the
Wellington, Marlborough, Nelson, Otago, and Southland
regions. Ultic Soils cover 3% of New Zealand (Fig. 16.2).
Beyond the north Waikato and Auckland-Northland regions,
Ultic Soils occur on generally stable hills or old terraces in
landscapes where the weathering surfaces have survived for
at least hundreds of thousands, possibly millions, of years.
16.1.3 Variation Within the Ultic Soil Order
Five soil groups are defined within the Ultic Soil order in the
New Zealand Soil Classification (Fig. 16.3) as follows.
Densipan Ultic Soils—have a densipan (an Ed horizon)
which is usually just below the topsoil (upper subsoil). The
densipan has a high soil dry bulk density, very high soil
strength, and high penetration resistance although it is not
Fig. 16.2 Distribution of Ultic
Soils
16.1 Important Features of Ultic Soils
251
australis). Limited areas of Ultic Soils occur in the
Wellington, Marlborough, Nelson, Otago, and Southland
regions. Ultic Soils cover 3% of New Zealand (Fig. 16.2).
Beyond the north Waikato and Auckland-Northland regions,
Ultic Soils occur on generally stable hills or old terraces in
landscapes where the weathering surfaces have survived for
at least hundreds of thousands, possibly millions, of years.
16.1.3 Variation Within the Ultic Soil Order
Five soil groups are defined within the Ultic Soil order in the
New Zealand Soil Classification (Fig. 16.3) as follows.
Densipan Ultic Soils—have a densipan (an Ed horizon)
which is usually just below the topsoil (upper subsoil). The
densipan has a high soil dry bulk density, very high soil
strength, and high penetration resistance although it is not
Fig. 16.2 Distribution of Ultic
Soils
16.1 Important Features of Ultic Soils
251