86 Development and Activities of Roots of Crop Plants. 



is normal for eastern Nebraska (Weaver, 1920), while the moist subsoil at 

 the latter station may have resulted from the heavy precipitation (11 inches 

 above normal) during 1919. At BurUngton a total of 2.3 inches of rain 

 fell on June 18 to 21, but by June 30 no moisture was available for growth at 

 any level (table 25). 



Soil-temperatures were much higher during this period, especially in 

 the drier soils at PhilUpsburg and Burhngton, where an increase of 4* or 

 5° F., even at depths of 3 or 4 feet, occurred. Air-temperatures remained 

 relatively high, with the characteristic sequence of day and night temper- 

 atures for the several stations already noted (fig. 37). The great range 

 of temperature and humidity at BurUngton from day to night and the low 

 night temperatures were not inducive to rapid growth. Average daily 

 evaporation during the period ranged from 24 to 62 c. c. at Burhngton, from 

 22 to 28 c. c. at PhilUpsburg, while at Lincoln it varied from 8 to 17 c. c. 

 Table 28. — Relative development of crops, 1921. 



» Many stalks were only 2 to 4 inches tall and had been dead for some time. 

 » Average length of heads without awns. 



Data on the development of the crops at the several stations at the time 

 of harvest is given in table 28. An examination of table 28 shows in every 

 case, as in 1920, a decrease in height of the crop from the more humid to the 

 more arid stations. The same general relation holds for the average number 

 of stalks per square meter, except at BurUngton, where many tiny stalks, 

 only 2 to 4 inches taU, started growth relatively early and soon dried out, but 

 remained until harvest. During 1920 the average number of stalks per 

 square meter at BurUngton was from one-third to one-half less than at the 

 other stations, although the number at PhilUpsburg often exceeded that at 

 Lincoln. The average number of stalks per plant (1921) was in direct rela- 

 tion to the water-content of soil and other factors favorable or unfavorable 

 to plant-growth. In general, this relation held also during 1920. The 

 average number of heads per square meter and the average length of heads 

 or panicles decreased from Lincoln to PhilUpsburg and BurUngton respectively. 



