Ultic Soils [U]
Probably the first New Zealand soil to be cultivated by steel implements, by men under the command of Marion de Fresne in 1771 in the Bay of Islands.
Ultic Soils are strongly weathered soils that have a well-structured, clay enriched subsoil horizon. An E horizon, which is relatively depleted in clay, frequently occurs immediately beneath the topsoil. The soils are acid and strongly leached, with generally low levels of calcium and other basic cations. They occur in clay or sandy clay material derived by strong alteration of quartz-rich rocks over long periods of time.
Ultic Soils are most common in the northern North Island, and in the Wellington, Marlborough, and Nelson regions. They cover 3% of New Zealand.
Clayey subsoils with slow permeability are characteristic. Soils have dispersible surface horizons susceptible to livestock treading damage, and are prone to erosion.
Soils are strongly acid with low nutrient reserves. There is a small content of weatherable minerals. Kaolin and vermiculite are the dominant clay minerals.
Soils have a large and active population of soil organisms in topsoils.
Soil orders are divided into soil groups based on variation in factors such as drainage status, parent material, chemical and physical properties