7. Melanic Soils

Melanic Soils make up about 1% of New Zealand’s soils and are scattered throughout the country where soils are developed on calcium- or magnesium-rich rocks. Melanic Soils form on limestone, marble, calcareous sandstone, and mafic to ultramafic rocks. Melanic Soils occur on limestones that outcrop throughout New Zealand, but particularly along the east coast in Hawke’s Bay, Wairarapa, Marlborough, and Otago. They also form on ultramafic rocks in northwest Nelson. The most extensive areas of Melanic Soils are in coastal North Otago on limestone and mafic volcanic rocks (basalts and tuffaceous greywackes). Topsoils are black (giving the soil order its name), deep, and rich in soil organic matter, and smectite clays, that bind the soil together forming strong stable aggregates. The upper subsoil is often relatively thin grading into the underlying parent rocks. Melanic Soils are rich in calcium and/or magnesium which contribute to high natural fertility and near neutral to slightly alkaline soil pHs. The underlying rock forms a physical barrier, limiting root penetration, but water may drain through the cracks. The clayey materials of Melanic Soils are used for cricket pitches because of their strong shrink-swell character. Truffles can form a niche crop on some alkaline Melanic Soils.