Chemical nature of soil organic matter under grassland and recently established forest

Carbon-13 (C-13) solid-state NMR spectroscopy was used to investigate the c hemical nature of organic C in mineral topsoil sampled under grassland and adjacent recently established (10-17 years old) coniferous forest (Douglas fir, Pseudotsuga menziesii; Ponderosa pine, Pinus ponderosa; Corsican pine, Pinus nigra) at two sites (Craigieburn, Cave Stream) in the South Island o f New Zealand. This involved using a Cross-Polarized/Magic-Angle Spinning ( CP/MAS) technique to identify different chemical forms of soil organic C, w hilst Proton Spin Relaxation Editing (PSRE) was used to determine different 'pools' of soil organic C. Results obtained from the Craigieburn soils (0- 5 cm) were more promising than those obtained from the Cave Stream soils (0 -10 cm) because the total Fe content was smaller, and indicated a shift tow ards more recalcitrant forms of organic C in soil under trees compared with grassland, which might reflect reduced inputs of fresh organic matter to t he soil under trees.