Fig. 1. Dye and ammonium carbonate infiltration into two initially dry soils. Pictures (a), (b), (c) show wetting front propagation in the Hanford sandy loam; (d), (e), (f) show the process in the Delhi sand. Pictures (c) and (f) show that the wetted but unstained areas by the blue dye became red after application of the proposed pH indicator.

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