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ORIGINAL RESEARCH

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

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

Received 29 August 2008.

Ancillary information, such as apparent electrical conductivity (EC_a), can improve the spatial and temporal estimation of soil properties. The purpose of this study was to determine if EC_a 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 EC_a maps showed clear differences between the conventional tillage and direct drilling plots, with higher EC_a and SOC in the direct drilling plots. A normalized EC_a difference (EC_a), calculated as the difference between the normalized vertical and horizontal dipole EC_a values (EC_aV and EC_aH, respectively) successfully classified the SOC observations according to their corresponding management systems. Maps of EC_a (FKM1) and EC_aV and EC_aH (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 EC_a and SOC, EC_a was shown to be useful for the spatial estimation of SOC.

Abbreviations: CT, conventional tillage • DD, direct drilling • EC_a, apparent electrical conductivity • EC_aV, vertically sensed apparent electrical conductivity • EC_aH, 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 • EC_a, normalized apparent electrical conductivity difference