The soil redox potential (Eh) can provide essential information to characterise soil conditions. In practice, however, numerous problems may arise regarding: (i) Eh determination in soils, especially aerobic soils, e.g. variations in the instrumentation and methodology for Eh measurement, high spatial and temporal Eh variability in soils, irreversibility of the redox reaction at the surface electrode, chemical disequilibrium; and (ii) measurement interpretation. This study aimed at developing a standardised method for redox potential measurement in soils, in order to use Eh as a soil quality indicator. This paper presents practical improvements in soil Eh measurement, especially regarding the control of electromagnetic perturbations, electrode choice and preparation, soil sample preparation (drying procedure) and soil:water extraction rate. The repeatability and reproducibility of the measurement method developed are highlighted. The use of Eh corrected at pH7, pe+pH or rH2, which are equivalent notions, is proposed to facilitate interpretation of the results. The application of this Eh measurement method allows characterisation of soil conditions with sufficient repeatability, reproducibility and accuracy to demonstrate that conservation agriculture systems positively alter the protonic and electronic balance of soil as compared to conventional systems.

Agrotest fyto Kromeriz Institute Havlíckova 2787 76701 Kromeriz Czech Republic

CIRAD PERSYST UPR 115 AIDA and AfricaRice Centre 01 BP 2031 Cotonou Benin

CIRAD US 49 Analyse Avenue Agropolis TA B 49 01 34398 Montpellier Cedex France

ENSAT INRA INP UMR AGIR BP 52627 Chemin de Borde Rouge 31326 Castanet Tolosan Cedex France

IDEEAQUACULTURE Parc Euromédecine 2 39 Rue Jean Giroux 34080 Montpellier France

La Boisfarderie Brives 36100 France

Le Cazals Castanet 81 150 France

UMR CNRS UdS 7140 Université de Strasbourg Institut Le Bel 4 rue Blaise Pascal CS 90032 Strasbourg 67081 France

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