Making use of knowledge obtained in preceding papers of the turbulent diffusion of both continuous fixed-source-type and instantaneous floating-source-type, the applications of diffusion theories to several agricultural techniques are theoretically dealt with. The dusting procedure of agricultural chemicals with the dusting machine and the extending procedure of smoke screen to prevent the frost damage to agricultural products are dealt with from the theoretical viewpoint following the continuous fixed-source-type diffusion theory. The surface distribution of concentration of chemicals from the dusting machine on the ground is expressed by the gaussian profiles and the area of the effective dusting region, whithin which the concentration is greater than a certain critical value χ_0*, is shown to be
A∞(Q/Uχ_0*)^2/(1+m),
where Q and U denote the source strength of dusting machine and the appropriate mean wind speed at the dusting outlet, respectively, and m is a number depending upon the thermal stratification of the atmospheric surface layer. From the preceding paper m is shown to be 1.5, 0.8 or 0.5 under the thermally unstable, neutral or stable conditions, respectively. The effective shading region of smoke screen is analogously discussed with the vertically integrated smoke concentration. In this case, the region does not depend upon the vertical characteristics of smoke screen and the area is shown to be in proportion to (Q²/‹v²›^1/2Uχ_z*), where ‹v²›^1/2 and χ_z* denote the lateral component of wind turbulence and a certain critical value of vertically integrated smoke concentration over which the shading is effective. The problems of diffusion area due to a battery of several smoke machines and to moving machines are discussed, too.
The aerial dusting from aircrafts of agricultural chemicals is dealt with as the floating-source-type diffusion during the time t from the release. The width l_* of effective swath is shown to be
l_*=√2/3ε^1/4t^3/4(ln3Q/√2πχ_*ε^1/2t^3/2),
where χ_* is the critical value of concentration and ε is the mean rate of turbulent energy dissipation within the height from the ground surface to the dusting aircraft. The maximum of the effective swath is obtained under the condition of t=0.477 (3Q/√2πχ_*ε^1/2)^2/3. This problem is similar to that of the smoke dissipation time and the application of smoke dissipation time as a measure to the aerial dusting procedure is discussed. The importance of micrometeorological elements, such as the mean wind velocity, the fluctuations in wind direction, and the temperature difference between two heights, are stressed, and the possibility of artificial control of diffusion phenomena through the modification of micrometeorological conditions is pointed out. Finally, the general calculation methods of air pollution are discussed only briefly.

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