June 26, 1916 Water Requirement of Corn and Sorghum 



477 



SCREENED INCLOSURE 



The plants were grown in a screened shelter in order to protect them 

 from the hailstorms and severe winds that are frequent in this region. 

 The inclosure was 20 feet square and had a flat top 10 feet from the 

 ground. It consisted of a framework of 2 by 4 inch studding spaced 

 3 feet apart and covered on both the top and sides by a wire netting 

 with a X-inch mesh. Cheesecloth w^as placed around the sides of the 

 inclosure to a height of 4X f^^t from the ground. This was held in 

 position by poultry netting tacked over the outside (PI. LXX, fig. i). 



The bottom of the inclosure was provided with a smooth, rigid floor 

 made of matched pine lumber. The cans were placed in three double 

 rows running north and south inside the inclosure, with a space of 2 feet 

 between each row. The height of the floor was such that the upper sur- 

 face of the cans came to within i^ feet of the top of the cheesecloth. 



The rate of evaporation inside and outside the shelter was determined 

 by two Livingston * porous-cup atmometers. These were renewed every 

 three or four weeks. They were connected with burettes which were 

 graduated to o.i c. c, and readings were made twice each day. The 

 atmometer outside the inclosure was placed at a distance of 2 feet from 

 the ground in the center of a plot that was planted to com. The atmom- 

 eter in the inclosure was placed a few inches above the upper surface 

 of the cans during the early part of the growing season and 2 feet above 

 their tops when the plants had reached 3 feet in height. The monthly 

 evaporation for the two seasons from the porous-cup atmometers, 

 having a coefficient of 0.74 is given in Table II. 



Table II. — Monthly evaporation (in cubic centimeters) inside and outside the screened 

 inclosure for igi4 and igi^ 



Period. 



Ratio. 



1914 



June 10 to July 10 



July 10 to Aug. 10 



Aug. 10 to Sept. 10 



1915- 



June 10 to July 10 



July 10 to Aug. 10 



Aug. 10 to Sept. 10 



The rate of evaporation within the inclosure as measured by the 

 porous-cup atmometers, was only approximately two-thirds as high as 

 that in the field. Briggs and Shantz ^ found that plants grown in such 

 a shelter had a water requirement approximately 20 per cent lower than 



' Livingston, B. E. The Relation of Desert Plants to Soil Moisture and to Evaporation. 78 p., illus., 

 Washington, D. C, 1906. (CarneKie Inst. Washincton, Pub. 50.) Literature cited, p. 77-7H. 



Operation of the porous-cup atmometer. In Plant World, v. 13, no. 5, p. 111-119. 1910. 



» Briggs, L. J., and Shantz, H. L., 1913- Op. cit. 



