7
Melanic Soils
The Melanic Soil looks just fine
with a pH near to alkaline
formed on limestone or on marble
the black topsoil is a marvel
Abstract
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.
7.1 Important Features of Melanic Soils
7.1.1 Concept and Key Features of the Soil
Order
Melanic Soils are formed from parent materials rich in calcium carbonate (lime), mainly limestone, marble, and calcareous sandstone, or dark-coloured basic (magnesium- and
iron-rich) volcanogenic rocks (basalt, tuffaceous greywacke)
or ultramafic rocks (dunite, serpentinite, peridotite).
Melanic Soils are well structured and naturally fertile
with particularly dark to black, deep, A horizons (topsoils),
thin B or AB horizons, and parent rock (R or CR horizons)
within about 60 cm of the soil surface (Fig. 7.1). The soil
clay is dominated by smectites, notably montmorillonite,
which cause the soil to shrink and crack markedly on drying,
and to swell on wetting. The clay mineralogy, together with
the high soil organic matter content, promotes a
well-developed resilient soil structure.
The high natural fertility is indicated by high saturation of
the cation exchange capacity, especially with calcium and
magnesium ions. Due to the lime-rich parent materials, soil
acidity is generally mild and some Melanic Soils are even
slightly alkaline, helping enable humus to spread through the
topsoil.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. E. Hewitt et al., The Soils of Aotearoa New Zealand, World Soils Book Series,
https://doi.org/10.1007/978-3-030-64763-6_7
101
Melanic Soils
The Melanic Soil looks just fine
with a pH near to alkaline
formed on limestone or on marble
the black topsoil is a marvel
Abstract
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.
7.1 Important Features of Melanic Soils
7.1.1 Concept and Key Features of the Soil
Order
Melanic Soils are formed from parent materials rich in calcium carbonate (lime), mainly limestone, marble, and calcareous sandstone, or dark-coloured basic (magnesium- and
iron-rich) volcanogenic rocks (basalt, tuffaceous greywacke)
or ultramafic rocks (dunite, serpentinite, peridotite).
Melanic Soils are well structured and naturally fertile
with particularly dark to black, deep, A horizons (topsoils),
thin B or AB horizons, and parent rock (R or CR horizons)
within about 60 cm of the soil surface (Fig. 7.1). The soil
clay is dominated by smectites, notably montmorillonite,
which cause the soil to shrink and crack markedly on drying,
and to swell on wetting. The clay mineralogy, together with
the high soil organic matter content, promotes a
well-developed resilient soil structure.
The high natural fertility is indicated by high saturation of
the cation exchange capacity, especially with calcium and
magnesium ions. Due to the lime-rich parent materials, soil
acidity is generally mild and some Melanic Soils are even
slightly alkaline, helping enable humus to spread through the
topsoil.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. E. Hewitt et al., The Soils of Aotearoa New Zealand, World Soils Book Series,
https://doi.org/10.1007/978-3-030-64763-6_7
101