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ŠUMARSKI LIST 1-2/2011 str. 23     <-- 23 -->        PDF

M. Kobal, M. Urbančič, N. Potočić, B. De Vos, P. Simončič: PEDOTRANSFER FUNCTIONS FOR BULK DENSITY... Šumarski list br. 1–2, CXXXV (2011), 19-27


Table 1 Summary information of soil profiles included in the study, grouped
chloride following ISO 10390 on


pH was determined in calcium


according toWorld Reference Base soil reference groups (SRG)


Tablica 1.Zbirni podaci o profilima tla uključenim u studiju, grupiranima prema


automatic pH-meter Metrohm Ti-


WRB referentnim grupama tala (SRG)


trino, C and N content using dry


combustion using ISO 10694
and/or 13878 on Leco CNS-2000,
carbonates following ISO 10693
with Scheibler calcium-meter (Eijkelkamp)
and soil texture following
ISO 11277 with sedimentary method
and pipette according to Köhn.


SRG
Referentna grupa N
Soil depth, cm
Dubina tla, cm
Elevation, m
Nadmorska visina, m
tala prema WRB mean SD min max
Acrisol
Cambisol
Fluvisol
Histosol
Leptosol
Luvisol
Phaeozem
Planosol
2
23
1
2
1
9
6
1
135
77
120
73
33
83
57
100
21.2
24.0
23.3
30.6
20.6
110
262
188
1227
720
316
532
383
557
1318
188
1497
720
910
1208
383


2.2 Statistical analyses and model comparison


Statističke analize i usporedba modela


In total, 109 soil samples were included in the statistical
analyses.Three influential points (soil samples)
according to Cook’s distance were excluded from further
analysis.The simple and multiple regression models
were used to predict.b from different explanatory
variables. According to PTFs, developed by Hoekstra
and Poelman (1982), van Wallenburg
(1988) and Reinds et al. (2001), regression models
with segmented relationships were also tested. Only
variables that show statistical significance at the 0.05
level were included in the models. Models were compared
using partial F-test.


From the literature, four different published PTFs
were selected (Jeffrey, 1970; Harrison et al.,


1981; Tamminen, 1994; Kaur et al., 2002) using
following equations:


Jeffrey:


Harrison:
Tamminen:
Kaur:


and Loss-On-Ignition method, the equation according
toCraftet al.(1991)was used:


The local PTF was compared with published PTFs
using four validation indices: mean predicted error
(MPE), standard deviation of the prediction error
(SDPE), root mean square prediction error (RMSPE)
and coefficient of determination(R2 ).These indices are
defined as:


3


where.bis soil bulk density (g/cm),OCis OC concentrationby
dry combustion method,LOIis organic


ith


matter content (g/kg) by Loss-On-Ignition method, Where.b,i is measured bulk density of soil sam-
Clayis percentage of a clay fraction (0-2 µ) andSiltis ple,.bp,i is predicted bulk density ofith soil sample,nis
percentage of silt fraction (2-63 µ). For conversion of the number of soil samples,covis the covariance and
the data on OC obtained by dry combustion method varis the variance.


2.3 Carbon stock calculation (C )


Izračun zalihe ugljika (Cpool)
pool


Carbon stock per given area, hectare in our case, WhereOCiis organic carbon concentration of ith soil
ith


was calculated using following equation: horizon, is thickness of soil horizon (in m), is


di .b,i


ith 3


bulk densityof soil horizon (in g/cm),stoni is a corith


rection factor for stoniness in horizon and n is the
number of soil horizons for a given soil profile.