
%0 Journal Article
%A Carter, M. R. 
%A Skjemstad, J. O. 
%A MacEwan, R. J. 
%T Comparison of structural stability, carbon fractions and chemistry of krasnozem soils from adjacent forest and pasture areas in south-western Victoria
%J Soil Research
%D 2002/03/13
%V 40
%N 2
%P 283-297
%K macroorganic carbon, soil aggregation, charcoal, photo-oxidation, potato rotation, CP/MAS 13C NMR spectroscopy.
%R https://doi.org/10.1071/SR00106
%U https://www.publish.csiro.au/paper/SR00106 
%X Basalt-derived krasnozems are generally well-structured soils; however, there is a concern that intensive agricultural practices may result in an adverse decline in soil organic carbon, organic matter chemistry, and structural quality over time. A study was conducted on loam to silty clay loam krasnozems (Ferrosols) near Ballarat in south-western Victoria to assess changes in soil C, soil structural stability, and C chemistry, at the 0&#8211;10 cm soil depth, under 3 paired sites consisting of adjacent long-term forest (Monterey pine or eucalyptus) v. 30 year cropping &lsqb;3 year pasture&#8211;2 year crops (potato and a root crop or grain)&rsqb;. Soil structural stability was also characterised in the A and B horizons under long-term eucalyptus and several cropped sites. Organic C levels in the A horizons for all the soils were relatively high, ranging from 46 to 89 g&sol;kg. A lower organic C (30&percnt;), associated mainly with loss of the sand-sized (>53 m) macro-C fraction, and a decrease in exchangeable Ca and Mg was found in the agricultural soils, compared with forest soils. Physically protected C in the <53 m fraction, as indicated by UV photo-oxidation, was similar among soils. Wet sieving indicated a decline of both C and N concentration in water-stable aggregates and the degree of macro-aggregation under agricultural soils, compared with the forest soils. However, soil structural changes under cropping were mainly related to a decline in the >5 mm sized aggregates, with no deleterious increase in the proportion of 0.10 mm aggregates. Solid state 13C NMR spectroscopy indicated a decrease in O-alkyl and alkyl C under pasture and cropping compared with forest soils, which was in agreement with the decline in the macro-C fraction. Characterisation of C chemistry following UV photo-oxidation showed that charcoal C (dominant presence of aryl C) accounted for 30&percnt; of the total soil organic C, while other functional groups (polysaccharides and alkyl C) were probably protected within micro-aggregates. Based on soil organic C and aggregate stability determinations alone, the implications for soil physical quality, soil loss, and diffuse pollution appear minimal. macroorganic carbon, soil aggregation, charcoal, photo-oxidation, potato rotation, CP&sol;MAS 13C NMR spectroscopy. 
