Investigations at Burlington, Colorado. 



63 



uted rainy periods gave a total of 1.2 inches. In fact this, coupled with the 

 high fertility of the soil (table 16), undoubtedly accounts for the very marked 

 early growth and the abundance of tillers, both phenomena being detri- 

 mental to the crops at a later period. 



Table 17. — Water-content in excess of hygroscopic coefficient in crop plats at Burlington, 1920. 



On June 3 a small margin of available water (3 to 5 per cent) still occurred 

 in the first 3 feet of soil, but by June 12 a deficiency was indicated by the 

 behavior of the plants. As a result of the drought (no rain in sufficient 

 amount to wet the soil had fallen from June 1 to 12), many of the leaves 

 were rolled and some did not recover their turgidity even during the night. 



Temperatures during the last half of April were low, falhng below 32° F. on 

 11 nights. The mean monthly temperatures for April and May were 41.2° 

 and 57.8° F. respectively. Frost occurred on May 15 and did some injury 

 to the crops. Only 3 clear days occurred in April and 5 in May. During 

 the last week of this interval the soil-temperature at a depth of 6 inches (in 

 an adjacent area of grassland) averaged 65° F. while the air temperature 

 gave an average of 80° F. during the day (maximum 100° F.) and 57° F. by 

 night (minimum 43° F.). The evaporating power of the air was 47 c. c. per 

 day, 85 per cent of which normally occurs during the hours of daylight, 

 the humidity often falling to 15 per cent or less. These aerial conditions, 

 coupled with the low water-content of the soil, readily explain the semi- 

 wilted condition of the crops. The soil in the plat where the wheat was 

 excavated was underlaid at a depth of 2.7 feet with a rather poorly devel- 

 oped, hght-colored hardpan, which, like the more ashy loess beneath, was 

 very dry. 



Root counts were made on a large number of plants. The number of 

 roots varied from 15 to 19. Not infrequently 5 to 9 of the younger ones had 

 grown an inch or two and died, apparently from drought. The extreme 

 depth reached by several roots was 2.5 to 2.7 feet, although a single root was 

 traced in the soil of an ancient rodent's burrow, where water had penetrated, 

 to a depth of 3.3 feet. However, the working depth of the root system as a 

 whole was only 1.3 feet. The plants had a wide lateral spread, and not in- 

 frequently roots extended laterally for 10 or 12 inches in the surface 6 inches 

 of soil. Others gave a maximum horizontal spread of 1.2 feet in the surface 

 foot. The entire root system was much more profoundly branched than 



