COMPARISON OF 13C CPMAS NMR AND CHEMICAL TECHNIQUES FOR MEASURING THE DEGREE OF DECOMPOSITION IN VIRGIN AND CULTIVATED PEAT PROFILES

Abstract

Solid-state ¹³C CPMAS NMR was used to examine organic soils from virgin, 5-yr and 15-yr cultivated sites. In agreement with previous studies using other techniques, the chemical effects of cultivation were essentially confined to the plough layer. Cultivated sites had less carbohydrate, and increased lipid and methoxyl carbon; these changes were similar to those found with depth, due to natural decomposition. Changes in aromatic and phenolic carbon with depth or years of cultivation were small. When the NMR data were compared with other indicators of decomposition, there were no correlations between the pyrophosphate index and NMR parameters. Rubbed fiber correlated positively with carbohydrate, and negatively with lipid. This study supports the use of rubbed fiber as a routine indicator of the degree of decomposition, and the use of ¹³C CPMAS NMR for elucidating chemical changes in organic soils. It also illustrates the need to separate more clearly chemical changes occurring during decomposition or cultivation, from purely physical changes due to drying, compaction, and particle size diminution. Key words: ¹³C NMR, degree of composition, peat profile, organic soils