near Mt Tarawera (Fig. 14.4) with a tephra fall-derived
parent material, the Rotomahana Mud erupted during the
Tarawera eruption of 10 June 1886, containing *30% clay
from weathering prior to its eruption. Soil dry bulk densities
tend to be relatively high in subsoils but somewhat lower in
topsoils. Recent Soils are usually deep rooting unless rock or
dense clay is present. Consequently, except for rocky or
stony soils, Recent Soils typically have high-profile
plant-available water capacity. Good drainage is common
except where there are shallow water tables.
14.4.3 Chemical Properties
Recent Soils generally have slightly acid to moderately acid
pHs, low organic carbon, and low P retention (Fig. 14.8,
Table 14.2). In Fluvial Recent Soils, organic carbon values
may fluctuate in the subsoil with the presence of buried
soils. Recent Soils are usually naturally fertile and base
saturations are usually high (meaning the cation exchange
complex of the soil is well supplied with the cations calcium, magnesium, potassium, and sodium) except in high
rainfall areas where soils are likely to be more leached and
acidic.
14.4.4 Biological Properties
A continuous cover of vascular plants is normally well
established. Recent Soils are among New Zealand’s most
productive and versatile soils, and if soil productivity is used
as an indicator of soil biological health, then under good
management the soils are expected to favourably support soil
biodiversity.
Fig. 14.7 Median and upper and
lower quartiles of clay content,
soil dry bulk density (t m
−3
), and
total available water holding
capacity for Recent Soils in the
New Zealand Soil Data
Repository
Table 14.1 Typical example of
physical properties for a
Weathered Fluvial Recent Soil
(Waimakariri series, SB10105)
Horizon
Depth
(cm)
Sand
(%)
Silt
(%)
Clay
(%)
Dry bulk density
(t m
−3
)
RAW
(%)
TAW
a
(%)
Ap1
0–18
33
49
17
1.2
12.7
26.0
Ap2
18–27
33
49
17
BA
27–38
41
46
12
1.4
11.5
18.4
Bw
38–46
48
43
8
1.3
13.3
20.3
Cu1
46–54
58
37
4
Cu2
54–80
76
19
4
1.4
9.2
17.0
Cu3
80–113
59
34
6
1.4
9.2
17.0
Cu4
113–124
60
32
7
2bBw1
124–134
14
63
22
2bBw2
134–160
24
57
18
a RAW = readily available water, TAW = total available water, both in % by volume
14.4 Key Soil Properties
225
parent material, the Rotomahana Mud erupted during the
Tarawera eruption of 10 June 1886, containing *30% clay
from weathering prior to its eruption. Soil dry bulk densities
tend to be relatively high in subsoils but somewhat lower in
topsoils. Recent Soils are usually deep rooting unless rock or
dense clay is present. Consequently, except for rocky or
stony soils, Recent Soils typically have high-profile
plant-available water capacity. Good drainage is common
except where there are shallow water tables.
14.4.3 Chemical Properties
Recent Soils generally have slightly acid to moderately acid
pHs, low organic carbon, and low P retention (Fig. 14.8,
Table 14.2). In Fluvial Recent Soils, organic carbon values
may fluctuate in the subsoil with the presence of buried
soils. Recent Soils are usually naturally fertile and base
saturations are usually high (meaning the cation exchange
complex of the soil is well supplied with the cations calcium, magnesium, potassium, and sodium) except in high
rainfall areas where soils are likely to be more leached and
acidic.
14.4.4 Biological Properties
A continuous cover of vascular plants is normally well
established. Recent Soils are among New Zealand’s most
productive and versatile soils, and if soil productivity is used
as an indicator of soil biological health, then under good
management the soils are expected to favourably support soil
biodiversity.
Fig. 14.7 Median and upper and
lower quartiles of clay content,
soil dry bulk density (t m
−3
), and
total available water holding
capacity for Recent Soils in the
New Zealand Soil Data
Repository
Table 14.1 Typical example of
physical properties for a
Weathered Fluvial Recent Soil
(Waimakariri series, SB10105)
Horizon
Depth
(cm)
Sand
(%)
Silt
(%)
Clay
(%)
Dry bulk density
(t m
−3
)
RAW
(%)
TAW
a
(%)
Ap1
0–18
33
49
17
1.2
12.7
26.0
Ap2
18–27
33
49
17
BA
27–38
41
46
12
1.4
11.5
18.4
Bw
38–46
48
43
8
1.3
13.3
20.3
Cu1
46–54
58
37
4
Cu2
54–80
76
19
4
1.4
9.2
17.0
Cu3
80–113
59
34
6
1.4
9.2
17.0
Cu4
113–124
60
32
7
2bBw1
124–134
14
63
22
2bBw2
134–160
24
57
18
a RAW = readily available water, TAW = total available water, both in % by volume
14.4 Key Soil Properties
225