area which gives the Organic Soils high cation exchange
capacities (CEC) mostly ranging from 40 to 170 cmol
(+)
kg
−1 . The high net negative charge varies markedly with pH.
Soil nitrogen levels are usually low and hence C/N ratios
range from 18 to as high as 70 in unfertilized and uncultivated Organic Soils.
Nutrient deficiencies are common (including nitrogen,
phosphorus, potassium, and sulphur). The trace elements
copper, selenium, and molybdenum are also frequently
deficient for crops and pasture.
8.4.5 Biological Properties
Restiad bogs were historically present from near Kaitaia to
the low-lying land south of Hamilton and between
Fig. 8.9 Median and upper and
lower quartile of clay content, soil
dry bulk density (t m
−3
), and soil
total available water holding
capacity for Organic Soils in the
New Zealand Soil Data
Repository
Table 8.2 Example of physical
properties of an Acid Fibric
Organic Soil under pasture
(Rukuhia series, SB09948,
SWAMP)
Horizon
Depth (cm)
Dry bulk density (t m
−3
)
RAW
a (%)
TAW
a (%)
Total porosity (%)
Of1
0–7
0.25
19.0
51.7
84
Of2
7–15
0.23
16.7
52.0
85
Of3
15–37
0.10
25.5
63.2
93
Om
37–49
0.15
26.1
61.8
93
2C
49–52
0.16
25.2
58.9
91
3Of
52–80
0.08
27.2
64.3
94
a RAW = Readily available water, TAW = total available water, percentage by volume
Fig. 8.10 Median and upper and
lower quartiles of soil pH, organic
carbon, and phosphorus retention
for Organic Soils in the NZ Soil
Data Repository
124
8 Organic Soils