b] ratio indicates better oxidation during anodic scan and less accumulation of oxidisable
species on the catalyst surface.
Mean standard deviations for total organic carbon (Dumas method) and oxidisable
organic carbon (Walkley and Black method) Source Method Mean standard deviation (cg C [g.sup.-1] soil) Intra-laboratory quality Dumas 0.076 control data from repeated analysis of standard soil Walkley and Black 0.101 samples used at DEDJTR Macleod Inter-Laboratory Proficiency Dumas 0.122 Program reported by the Australian Soil and Plant Analysis Council from 1997 Walkley and Black 0.271 to 2011 Table 3.
Soil analysis revealed a strong trend towards increasing total C content of soil, but only minor increases in oxidisable
organic C (by Walkley-Black method) were detected.
The amount of SOC determined using 5, 10, and 20mL of concentrated [H.sub.2][SO.sub.4] when compared with TOC allowed separation of TOC into the following 4 different fractions of decreasing oxidisability: fraction I ([C.sub.frac1]) organic C oxidisable
under 12N [H.sub.2][SO.sub.4]; fraction II ([C.sub.frac2]), the difference in SOC extracted between 18N and 12N [H.sub.2][SO.sub.4]; fraction III ([C.sub.frac3]), the difference in SOC extracted between 18 N and 24 N [H.sub.2][SO.sub.4] (the 24 N [H.sub.2][SO.sub.4] is equivalent to the standard WB method); and fraction IV ([C.sub.frac4]), residual organic C after reaction with 24 N [H.sub.2][SO.sub.4] when compared with TOC.
Many reports have shown that during the initial phase of decomposition, O-alkyl C is the first SOC component to decrease, as it is dominated by easily oxidisable
organic compounds (Mathers et al.
Pool I ([C.sub.VL] > very labile) organic C oxidisable
by 12.0N [H.sub.2]S[O.sub.4]
DOC concentration in the filtrate was measured using a total oxidisable
C analyser (Shimadzu, Japan).
According to the modified BCR sequential extraction method, heavy metals exist in soil in four fractions: acetic acid-soluble, reducible, oxidisable
and residual (Rodriguez et al.
(D) Walkley-Black oxidation, determined colourimetrically, converted from readily oxidisable
C using a factor of 1.72.
Fraction 1 (very labile): organic C oxidisable
under 12 N [H.sub.2]S[O.sub.4]; Fraction 2 (labile): difference in oxidisable
organic C extracted between 18 N and 12 N [H.sub.2]S[O.sub.4] (18 N-12N [H.sub.2]S[O.sub.4]); Fraction 3 (less labile): difference in oxidisable
organic C extracted between 24 N and 18 N [H.sub.2]S[O.sub.4] (24 N-18N [H.sub.2]S[O.sub.4]); and Fraction 4 (recalcitrant): difference in organic C extracted with 24 N [H.sub.2]S[O.sub.4] and TOC (TOC-24N [H.sub.2]S[O.sub.4]) (Benbi et al.
Physical and chemical properties of the farm soil and sediment Sand Silt Clay >20 [micro]m 2-20 [micro]m <2 [micro]m (%) Farm soil 0-0.10 m 85 9 5 Stream sediment 63 17 19 BD (C) OC (A) TN (B) (g/[cm.sup.3]) pH (D) Farm soil 0-0.10 m 1.3 0.07 1.5 7.9 Stream sediment 2.1 0.13 1.4 4.7 (A) Oxidisable
carbon content soil.
In the present study we investigated changes in total SOC, as well as in the concentration and distribution of oxidisable
organic carbon fractions in rhizospheric and bulk soils of Chinese pine following N addition in pot experiments.