The wind profile above a tall and very rough surface, in the case of adiabatic condition, is known to be represented by a formula such as u=u_*/k ln z-d/z_0 (1) where u is the wind velocity, z the height above the ground surface, u_*, the frictional velocity, d the zero-plane displacement, k von Kármán constant (=0.4), and z_0 the roughness length. Although d and z_0 were independently introduced into this formula, it seems from some observations i.e., Penman and Long (1960), Tani (1960), Udagawa (1966) and Allen (1968) that d and z_0 change with relation to each other. On the other hand, Takeda (1966) has theoretically deduced a following relation; 1/H-d ln H-d/z_0 = k^2/αH (2) where H is plant height and a constant (= 0.087). It is easily seen that three parameters which are characteristics to a very rough surface (H, d and z_0) are contained in eq. (2). Hence two of the three parameters, e.g., d and z_0 are intrinsically mutually independent. But if the variation of II due to the wind as in the case of the wind above the plant canopy is taken consideration, another condition will be imposed, and d and z0 will be no more mutually independent. Based on this consideration, Takeda shows that experimental results above mentioned can be theoretically explained. We also measured the wind profiles over a sorgo canopy in Fukuoka Prefecture, from July to August 1968, in succession to 1967. And obtaining d, z_0 and H from them, we have tried to find the relation between d, z_0 and H in the light of Takeda's theory (1966). Results obtained are summarized as follow: 1. The zero-plane displacement (d) decreased with the friction velocity (u_*) but increased with the pant height (H) and the mean leaf area density. These results are in accordance with those obtained by Udagawa (1963) over barley fields, but different from by Rider (1954) and Tani (1960). However, when the mean leaf area density decreased rapidly, a slight decrease in d was found though the plant height increased. 2. The roughness length (z_0) increased with u_*, H and rate of emergence, which is in agreement with the results obtained by Penman and Long (1960) over a wheat field and by Allen (1968) over a Japanese larch plantation. The change in z_0 with u_* became much larger after heading. The sorgo together with corn canopy seems to behave as a large leaf type according to Monteith's classification (1963). 3. The roughness height (H) decreased from the maximum value (almost equal to the measured plant height at low wind speed) to nearly constant value with the increase in u_*; the decrease is the fact that the theory expects. 4. Values of d and z_0 plotted on the rough surface diagram (Takeda, 1966) produced a curved line segment. The change of the place of the segment on the diagram brilliantly reflected the actual development of the plant canopy.
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