DRY-LAND GRAINS IN THE GREAT BASIN. 7 



EVAPORATION. 



Closely connected with the rainfall as a factor in cliy-land farming 

 is the evaporation. Tliis is determined by measuring daily the amount 

 of water that is lost from an open cylindrical tank placed in the 

 ground sO that the surface of the water in the tank is approximately 

 level with the surface of the ground. Where the evaporation is high 

 the amount of water required by crops and the difficulty of conserving 

 soil moisture are greater than where the evaporation is low. Hence 

 the danger of loss through drought is relatively greater. 



The evaporation at the Neplii substation, as determined during the 

 seasons of 1908 and 1909, is approximately 40 inches for the six 

 months beginning A\n-[\ 1. At Amarillo, Tex., for the same period it 

 is 50 inches; at North Platte, Nebr., 42 inches; and at Edgeley, 

 N.Dak., 28 inches.'' Neplii has an evaporation which is about the 

 average of the amounts determined at the various dry-land experiment 

 stations of the West. 



The amount of evaporation depends principally upon the relative 

 dryness of the atmosphere, the amount of wind, and the temperature. 

 When the dryness of the air or the amount of wind increases, or when 

 the temperature rises, the evaporation is greater. The substation is 

 now equipi)ed with instruments for determining the amount of 

 moisture in the atmosphere, the amount of wind, and the tempera- 

 tures. The work is done in cooperation with the Phj^sical Laboratory 

 of the Bureau of Plant Industry, by which the equipment is furnished. 



WIND. 



The amount of wind was determined at the substation from April 



1 to October 31, 1909. The anemometer was placed about 2 feet 

 above the ground near the evaporation tank. This determines the 

 amount of wind that passes directly over the water in the tank and 

 hence the amounts that directly affect the soil. During the seven 

 months beginning April 1 the wind recorded was 20,621.4 miles. 

 This gives an average velocity of 4 miles an hour for the entire season. 

 The average hourly velocity, as determined daily, varied from about 



2 miles to 8 miles. This shows that the wind at the substation is not 

 very high for any length of time. Compared with wind velocities on 

 the Great Plains, those at Nephi arc exceedingly low. They repre- 

 sent fairly the wind condition in the valleys of the Great Basin area. 



""Physical Problems in Connection with Dry Farming," by L. J. Briggs and 

 J. 0. Belz, in Proceedings, Third Dry-Farming Congress, Cheyenne, Wyo., 1909. 

 [Clr. 61J 



