Geoscience Reference
In-Depth Information
more emphasis on the vertical soil variation, such as topsoil thickness (Kitchen et al., 1999) and
depth of sand deposition (Kitchen et al., 1996).
Fields on morainic soils, which represent a significant proportion (>25 percent) of the areas used
for cereal production in Norway, typically show high variability in texture and organic matter, both
laterally and vertically. Nevertheless, most interest is normally paid to lateral variation in topsoil
properties. Reasons for this are that such variation may be directly observed in the field, and that
more quantitative information, such as soil analyses, usually exists for the upper layer than for those
below. Using the EM-EC
a
technique, however, the effective measuring depth goes much deeper than
the topsoil layer. Consequently, subsoil soil properties may affect the EM-EC
a
signal significantly.
It is thus of interest to explore how soil variation in deeper layers affects such measurements. The
objective of this study was to establish relations between measurements of EC
a
, soil texture, and
ignition loss at different depths on two morainic soils in southeast Norway, in order to evaluate the
suitability of the EM-EC
a
technique to map the texture and organic matter content of such soils.
12.2
MAteRIAl And MethodS
12.2.1 l
o c a t i o n is
Two locations were selected: a field at Apelsvoll Research Centre (60°42′ N, 10°51′ E, 250 m above sea
level) and the long-term experiment at Møystad (60°47′ N, 11°10′ E, 150 m above sea level). The soil at
both locations is an imperfectly drained brown earth (Gleyed melanic brunisolls, Canada Soil Survey)
with dominantly loam and silty sand textures (see Table 12.1), which is typical for the region.
12.2.2 eM-ec
a
d
e v i c e
The device used to measure EC
a
(EM38) has an intercoil spacing of 1 m and may be operated in
one of two measurement modes. In vertical mode (coil axes perpendicular to soil surface), the effec-
tive measuring depth is approximately 1.5 m, whereas in horizontal mode (coil axes parallel to soil
surface), the effective measuring depth is approximately 0.75 m. In the following, measurements of
tAble 12.1
Mean Soil properties at Apelsvoll (
n
= 18) and Møystad (
n
= 16)*
depth (cm)
Apelsvoll
Møystad
Soil
property
a
0-20
30-50
60-80
0-20
20-40
40-60
Gravel
b
200 (355)
236 (640)
182 (449)
163 (125)
202 (146)
228 (224)
Coarse sand
78.9 (210)
127 (580)
97.8 (320)
75.6 (40)
83.8 (60)
81.9 (70)
Medium sand
242 (130)
273 (290)
274 (270)
224 (60)
233 (50)
267 (170)
Fine sand
224 (100)
235 (210)
254 (310)
223 (40)
233 (50)
241 (280)
Total sand
b
544 (210)
631 (100)
628 (530)
558 (170)
544 (210)
554 (220)
Coarse silt
134 (80)
126 (130)
134 (140)
132 (30)
128 (40)
129 (70)
Medium silt
108 (80)
90.6 (110)
88.3 (110)
143 (40)
134 (40)
126 (50)
Fine silt
72.8 (40)
60.0 (70)
56.7 (100)
73.1 (30)
69.4 (30)
63.1 (60)
Total silt
b
316 (160)
273 (300)
276 (310)
344 (40)
330 (70)
316 (120)
Clay
b
142 (150)
95.0 (180)
96.7 (260)
121 (120)
121 (120)
118 (110)
Ign. loss
62.2 (51)
37.8 (41)
32.3 (46.7)
50.7 (60)
48.7 (57)
48.0 (57)
*
Ranges in parenthesis
a
Units: gravel given in g kg
−1
bulk soil, and other components in g kg
−1
fine earth (<2 mm).
b
Particle size of gravel: >2000 μm, total sand: 60 to 2000 μm, total silt: 2 to 60 μm and clay: <2 μm.
