Near-infrared reflectance spectroscopy (NIRS): a practical tool for the assessment of soil carbon and nitrogen budget

The assessment of greenhouse gas emissions from soils requires an accurate knowledge on the fate of carbon (C) and nitrogen (N) in soils. This knowledge shouldn't be limited to C and N stocks in soils but should incorporate the quantification of functional soil organic matter (SOM) fractions with different turnover rates. Conventional analysis can't be used to assess such functional properties of SOM over large geographical areas. Near-infrared reflectance spectroscopy (NIRS) is a rapid and cheap method that could achieve this goal. This technology has proven its efficiency to discriminate among functional SOM fractions and to predict C, N on large sets of soil samples at a large regional scale. NIRS can be used for the detailed analysis of decomposition and aggregation of SOM, two key ecosystem processes that control C and N budget in soils. This review points up the improvement of NIR prediction models by the technique of local calibration and the potential of NIR analysis to assess the ontogeny and heterogeneity of detritus in soils. Mapping soil C, N and SOM fractions at the European level is a challenge that NIRS can help to take up.