Multivariate Analysis of Ir, Nir, and Nmr Spectra of Soil Samples from Different Land Use Conversions: Native Forest, Pasture, and Plantation Forest

Mid infrared (IR), near infrared (NIR), and 13C nuclear magnetic resonance (NMR) spectra were recorded on solid soil samples from three neighbouring sites with similar history but different current land use — namely, native podocarp forest, pasture land cleared from native forest, and exotic softwood plantation converted from improved pasture. Principal component analysis and projection to latent structures regression of the spectra showed changes in carbohydrate and phenolic fractions reflected the current land use, with the introduction of pasture and plantation forest decreasing the aliphatic and increasing the aromatic fractions of the soils. Fractional areas for NMR spectra ranged between 0.16 and 0.34 for aliphatic, 0.33 and 0.50 for carbohydrate, 0.12 and 0.40 for aromatic, 0.04 and 0.11 for phenolic, and 0.01 and 0.17 for carbonyl carbon. High carbon concentrations in native forest micro-sites exhibiting low pH occurred predominantly as aliphatic and carbohydrate fractions, even at depths down to 0.5 m. Soil carbon protection following land use diversification was evident for at least 80 years.