. Soil physics and management. e. 304 SOIL PHYSICS AND MANAGEMENT Time Required and the Number of Plants that Came Up in the Soils of DifferentColors. One Hundred Seeds Were Planted in Each ^ Wheat Oats Corn Melons Days after planting Light Dark Light Dark Light Dark Light Dark 7 s 2951586265 4 758686868686 27 707575 75 6 80100100100100100 1 66 7272 684 959595 4 3257 8 9 10 21 11 60 12 85 13 86 With black the absorption is almost complete. The soils of what-ever color tend to cool to the temperature of the surroundingatmosphere during the night or in cloudy weather. The table onpage 302 shows
. Soil physics and management. e. 304 SOIL PHYSICS AND MANAGEMENT Time Required and the Number of Plants that Came Up in the Soils of DifferentColors. One Hundred Seeds Were Planted in Each ^ Wheat Oats Corn Melons Days after planting Light Dark Light Dark Light Dark Light Dark 7 s 2951586265 4 758686868686 27 707575 75 6 80100100100100100 1 66 7272 684 959595 4 3257 8 9 10 21 11 60 12 85 13 86 With black the absorption is almost complete. The soils of what-ever color tend to cool to the temperature of the surroundingatmosphere during the night or in cloudy weather. The table onpage 302 shows that the lowest temperatures of the dark-coloredsands were not as low as the light-colored ones. Color has littleinfluence in very wet soils since evaporation is a greater factor inlowering temperature than color is in raising it. 6. Latitude or Angle of the Suns Rays.—All flat areas ofthe earths surface have the same number of hours of possible sun-shine annually without regard to location on the earth. The effect i/erficat. Fig. 135.—Showing the comparative areas covered by the suns rays when vertical, 30, 60,and 80 degrees from the vertical. Compare AB, AC, AD, and AE. of the rays in warming the soil depends upon the angle at whichthey strike (Fig. 135). If a sunbeam striking the earths surfaceperpendicularly covers an area of 1, when this same beam strikesat an angle of 30 degrees from the vertical, it will cover an area ; at 60 degrees it will cover an area of 2, and at 80 degreesan area of 6. The heat will be spread over a larger area the greaterthe distance from the vertical, and the effect on temperature wouldbe inversely as the angle. The atmosphere absorbs some heat. The TEMPEEATURE 305 vertical ra3s pass through a thinner stratum of air than the other,and more heat will reach the surface from a vertical sun. Theeffect of greater inclination is compensated for in summer to someextent bj the longer sunshine period in tTvent5^-four hours for highlatitudes. 7.
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