The object of this study was to compare the electropotential-time patterns (PHYTOGRAMS) of invasive electrochemical sensors placed in the main stem of cotton subjected to two different irrigation regimes. The potentials were monitored every fifteen minutes for one hundred and five days. Results indicate the potentials dropped with irrigation and/or rainfall with variable magnitude and timing. The potential variations were first interpreted independent of any causative mechanism. Then, under the oxygen hypothesis, the potentials were interpreted in terms of oxygen utilization. The date set was processed into a daily PHYTOGRAM INDEX, PG1O. This numerical index indicated that the block with more abundant water and higher yield had a higher and more steady "respiration" rate than the dry block but the respiration rate of the two blocks converged following the main growing season.