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ORIGINAL RESEARCH

Can Apparent Electrical Conductivity Improve the Spatial Characterization of Soil Organic Carbon?

Gonzalo Martineza,*, Karl Vanderlindena, Rafaela Ordóñezb and José L. Muriela

a IFAPA, Centro Las Torres-Tomejil, Junta de Andalucía, Ctra. Sevilla-Cazalla, 41200 Alcalá del Río, Sevilla, Spain
b IFAPA, Centro Alameda del Obispo, Junta de Andalucía, Avda. Menéndez Pidal, s/n, 14080 Córdoba, Spain

Correspondence: * Corresponding author (gonzalo.martinez{at}juntadeandalucia.es).

Received for publication 29 August 2008. Ancillary information, such as apparent electrical conductivity (ECa), can improve the spatial and temporal estimation of soil properties. The purpose of this study was to determine if ECa could be used for the spatial characterization of soil organic C (SOC) within a long-term tillage experiment. Apparent electrical conductivity was measured using an electromagnetic induction sensor, the EM38DD, and its predictive potential for mapping SOC was evaluated. The ECa maps showed clear differences between the conventional tillage and direct drilling plots, with higher ECa and SOC in the direct drilling plots. A normalized ECa difference ({Delta}ECa), calculated as the difference between the normalized vertical and horizontal dipole ECa values (ECaV and ECaH, respectively) successfully classified the SOC observations according to their corresponding management systems. Maps of {Delta}ECa (FKM1) and ECaV and ECaH (FKM2) classified by fuzzy k-means accounted for 30% of the total SOC variability, whereas the individual plots and management strategy explained 44 and 41%, respectively. Simple kriging with local varying means using either FKM2 or plot-average SOC as secondary information reduced the RMSE by 8% and increased the efficiency index by about 70% compared with ordinary kriging. Despite the low point-to-point correlation between ECa and SOC, ECa was shown to be useful for the spatial estimation of SOC.

Abbreviations: CT, conventional tillage • DD, direct drilling • ECa, apparent electrical conductivity • ECaV, vertically sensed apparent electrical conductivity • ECaH, horizontally sensed apparent electrical conductivity • EMI, electromagnetic induction • FKM, fuzzy k-means • FKM1, fuzzy k-means classification for normalized apparent electrical conductivity difference data • FKM2, fuzzy k-means classification for vertically and horizontally sensed apparent electrical conductivity data • OK, ordinary kriging • SKlm, simple kriging with varying local means • SOC, soil organic carbon • {Delta}ECa, normalized apparent electrical conductivity difference






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