UNCORRECTED PROOF 1 2 Laboratory, field and airborne spectroscopy for monitoring organic 3 carbon content in agricultural soils 4 Antoine Stevens a, ⁎ , Bas van Wesemael a , Harm Bartholomeus b , Damien Rosillon c , 5 Bernard Tychon c , Eyal Ben-Dor d 6 a Department of Geography, Université catholique de Louvain, Place Pasteur, 3, 1348 Louvain-La-Neuve, Belgium 7 b Centre for Geo-Information, Wageningen University, Droevendaalsesteeg 3, NL 6708 PB, Wageningen, The Netherlands 8 c Department of Environmental Sciences and Management, University of Liège, Campus of Arlon, 185, avenue de Longwy, 6700 Arlon, Belgium 9 d Department of Geography and Human Environment, Tel Aviv University, P.O. Box 39040 Ramant Aviv, Tel Aviv, 69978, Israel 10 11 Received 22 December 2006; received in revised form 15 August 2007; accepted 12 December 2007 12 Abstract 13 The temporal evolution in Soil Organic Carbon (SOC) content is often used in estimations of greenhouse gas fluxes and is an important 14 indicator of soil quality. Regional estimates of SOC changes can only be obtained by analyzing very large number of samples over large areas due 15 to the strong spatial variability in SOC contents. Visible and Near Infrared Spectroscopy (VNIRS) provides an alternative to chemical analyses. 16 The benefits of this technique include a reduction of the sampling processing time, an increase of the number of samples that can be analyzed 17 within time and budget constraints and hence an improvement of the detection of small changes in SOC stocks for a given area. Carbon contents 18 are predicted from spectra through Partial Least Square Regressions (PLSR). The performance of three different instrumental settings (laboratory, 19 field and airborne spectroscopy) has been assessed and their relative advantages for soil monitoring studies have been outlined using the concept 20 of Minimal Detectable Difference. It appears that ground-based spectrometers give Root Mean Square Errors of Cross-Validation similar to the 21 limit of repeatability of a routine SOC analytical technique such as the Walkley and Black method (±1 g C kg - 1 ). The airborne spectrometer, 22 despite its greater potential to cover large areas during a single flight campaign, has some difficulties to reach such values due to a lower Signal-to- 23 Noise Ratio. Because of its statistical nature, the method and its potential rely on the stability of the calibrations obtained. It appears that 24 calibrations are currently site-specific due to variation in soil type and surface condition. However, it is shown that PLSR can take into account 25 both soil and spectral variation caused by different measuring campaigns and study areas. Further research is needed to develop regional spectral 26 libraries in order to be able to use VNIRS as a robust analytical technique for precisely determining the SOC content and its spatial variation. 27 © 2007 Elsevier B.V. All rights reserved. 28 29 Keywords: Soil Organic Carbon; Reflectance Spectroscopy; Partial Least Square Regression; Visible and Near Infrared Diffuse Reflectance Spectroscopy; Soil 30 carbon monitoring 31 32 1. Introduction 33 In the context of global environmental change, the estimation 34 of carbon fluxes between soils and the atmosphere has been the 35 object of a growing number of studies (Ryan and Law, 2005). 36 This has been motivated notably by the possibility to sequester 37 CO 2 into soils by increasing the Soil Organic Carbon (SOC) 38 stocks (Lal, 2004) and by the role of SOC in maintaining soil 39 quality. Within the EU soil thematic strategy, the decline of 40 organic matter is mentioned as one of the major threats to the 41 soil resource (Van-Camp et al., 2004). Even if a number of 42 studies have already demonstrated the impact of specific 43 management practices or land use changes on SOC stocks 44 (e.g. Johnson and Curtis, 2001, Guo and Gifford, 2002; West 45 and Post, 2002), several difficulties in estimating SOC stocks 46 and their temporal evolution remain challenging (Post et al., 47 2001). One of them is linked to the spatial variability of SOC 48 that masks its slow accumulation or depletion. Even at the field Available online at www.sciencedirect.com Geoderma xx (2008) xxx – xxx GEODER-09833; No of Pages 10 www.elsevier.com/locate/geoderma ⁎ Corresponding author. 3, place Pasteur, 1348 Louvain-La-Neuve, Belgium. Tel.: +32 10 47 28 61. E-mail address: antoine.stevens@uclouvain.be (A. Stevens). 0016-7061/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.geoderma.2007.12.009 ARTICLE IN PRESS Please cite this article as: Stevens, A., et al., Laboratory, field and airborne spectroscopy for monitoring organic carbon content in agricultural soils, Geoderma (2008), doi:10.1016/j.geoderma.2007.12.009