Roughness lengths (z(o)) and displacement heights (d) are often assumed to be simple functions of canopy height. This study was designed to evaluate these canopy aerodynamic properties for cotton (Gossypium hirsutum L.) having partial ground cover. Both z(o) and d were calculated from wind profile measurements for neutral conditions as defined with a Richardson number over irrigated and rainfed cotton in 1984 and 1985. Throughout the season z(o) started at 0.01 m and increased to a maximum of 0.20 m then declined to a value of 0.06 m when the canopy reached 70% ground cover. This change throughout the season was caused by the individual rows first acting as discrete bluff-bodies and then as a more uniform surface as the foliage elements overlapped as the canopy developed. Displacement heights increased linearly throughout the season as the canopy increased in height and leaf area.
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