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Two 70‐day‐old cotton plants (Gossypium hirsutum L. ‘Auburn 7‐683’) were subjected to a 26‐day drying cycle at the Auburn rhizotron in order to quantitatively study water relations and growth of both root and shoot as the soil dried. Measurements were made of rooting density changes; stem diameter and height increase; and soil water content (neutron meter), soil water potential (thermocouple psychrometer), and plant water potential (pressure chamber). Marked diurnal flurtuations in plant hydration and soil water potential were observed, especially during the middle of the drying cycle. Plant height increase and stem diameter growth slowed drastically after 17 days even though 35% of the root system was in soil wetter than −1 bar and the plant was rehydrating to a water potential of −3 to −5 bars. Plant water potential in the early morning did not equilibrate with the water potential of the wettest horizon of soil. The pattern of rooting with depth shifted during drying; initially, there were more roots in the upper layers of soil but, as a result of death of old roots in the top layers and production of new roots in the lower horizons of soil, rooting density increased with depth by the end of the drought. Cotton plants grown at the same time in a similar profile that was maintained moist did not show this reversal in rooting density.

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