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Oxygen Flux Measurement in Unsaturated Soils¹

ABSTRACT

Because in unsaturated soil systems the plateau of the current-voltage curve is not well developed or is absent, O₂ reduction at the platinum microelectrode is not diffusion controlled and consequently measured current depends continuously on applied potential. To overcome this difficulty an O₂ flux meter has been designed which carefully controls and measures the applied potential and enables the effective potential at the electrode to be measured precisely. The instrument, which has facilities for measuring soil electrical resistance, electrode redox potential, and O₂ reduction current is fully described together with a circuit diagram. Because the surface oxide condition of the microelectrode is crucial to reproducible results, electrode pretreatment involving gentle abrasion in wet fine sand is necessary to standardize conditions prior to measurement. The results show that the instrument is suitable for measuring O₂ flux in unsaturated systems, and that measured current is closely related to soil airspace.

¹ Research supported by the Dep. of Soil Science and Agrometeorology, Univ. of Natal, Pietermaritzburg, South Africa, the Dep. of Research and Specialist Services, Ministry of Agriculture, Rhodesia and the Dep. of Agronomy, Univ. of Georgia, Athens, GA 30602.

² Agronomist, Malcomess Ltd., Isando, South Africa, formerly Research Soil Scientist, Ministry of Agriculture, Marandellas, Rhodesia; and Professor of Agronomy, Univ. of Georgia, Athens, GA 30602, formerly Professor and Head of the Dep. of Soil Science and Agrometeorology, Univ. of Natal, South Africa.

Received for publication October 3, 1977. Accepted for publication July 11, 1978.