
TY  - JOUR
A1  - Clough, A. 
A1  - Skjemstad, J. O. 
T1  - Physical and chemical protection of soil organic carbon in three agricultural soils with different contents of calcium carbonate
JF  - Soil Research
JO  - Soil Res.
Y1  - 2000
VL  - 38
IS  - 5
SP  - 1005
EP  - 1016
KW  - charcoal, photo-oxidation, CP/MAS 13C NMR.
UR  - https://doi.org/10.1071/SR99102 
N2  - The amount of organic carbon physically protected by entrapment within aggregates and through polyvalent cation&#8211;organic matter bridging was determined on non-calcareous and calcareous soils. The composition of organic carbon in whole soils and &#60;53 m soil fractions was determined by 13C NMR analysis. High energy photo-oxidation was carried out on &#60;53 m fractions and results from the NMR spectra showed 17&#8211;40% of organic carbon was in a condensed aromatic form, most likely charcoal (char). The concept that organic material remaining after photo-oxidation may be physically protected within aggregates was investigated by treating soils with a mild acid prior to photo-oxidation. More organic material was protected in the calcareous than the non-calcareous soils, regardless of whether the calcium occurred naturally or was an amendment. Acid treatment indicated that the presence of exchangeable calcium reduced losses of organic material upon photo-oxidation by about 7% due to calcium bridging. These results have implications for N fertiliser recommendations based upon organic carbon content. Firstly, calcium does not impact upon degradability of organic material to an extent likely to affect N fertiliser recommendations. Secondly, standard assessment techniques overestimate active organic carbon content in soils with high char content. 
ER  -

