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Spread Surface: If fertilizer is added calculate carefully how much (See Chapter 19) to get the right amount per 1,000 square feet when the top-dressing is spread surface. The top-dressing should cover the soil to a depth of about a quarter of an inch. It is spread surface evenly, usually in spring or early fall, when the grass is dry, and is worked down among the grass with rake or broom.
Top-dressing not only supplies nutrients, it builds up a new surface layer of soil, stimulates and provides anchorage for new roots, covers the stolons of creeping bent and other grasses that spread surface by creeping surface stems. It fills minor depressions and restores evenness. On banks and sloping lawns this is of especial importance.
Bulk organic matter is important and of various kinds.
Where the surface is not permeable or wv"° impervious lenses intervene, surface spread surface; ineffective and recharge wells must be use^. ., survey has shown that this method has heen only moderately successful, however; wells may be more successful in resisting saltwater intrusion. Sewage reclamation for groundwater recharge appears to be thoroughly feasible if the heavy development costs are spread surface over a long period and if careful control is maintained to prevent pollution by poorly treated influents. A well system is more complicated and expensive than surface recharge, but in some regions it is the only practicable method, as in the rice fields of Arkansas, where an annual rainfall of 50 inches cannot percolate through the impermeable clay and silt on the surface.
The advancing light disturbance is at any moment spread surface over CD, the wave front. According to Huygens' principle, each point on the surface CD sends out a spherical pulse and we may construct the wave front an instant later when it reaches the water surface at E by constructing spheres of equal radii about all points in the surface CD. One such set of spheres will give the surface EF as its envelope, which is the new wave front at the instant considered. |
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