76 



Development and Activities of Roots of Crop Plants. 



The evaporating power of the air, which integrates, to a certain degree, 

 the factors of radiant energy, humidity, and wind movement, was greatest 

 throughout the season (23 to 60 c. c. average daily evaporation) at BurUngton, 

 intermediate at Phillipsburg (11 to 32 c. c), and least (9 to 25 c. c. at Lincoln 

 (fig. 36). 



Thus the conditions for crop-growth as regards rainfall, water-content of 

 soil, temperature, humidity, wind, and evaporation were most favorable 

 at Lincoln, intermediate at PhilUpsburg, and least favorable at Burlington. 

 These conditions are indicated by the native vegetation and borne out by the 

 growth of crops. 



The relative height of the mature oats and barley at the several stations 

 is shown in plate 3 (c/. also, plate 2 b, for wheat). These plates also show 

 the comparative yield from an average square meter; the bundle on the right 

 was taken in every case from the lowland plats at Lincoln. In table 19 may 



Table 19. — Summary of cereal crop development, 1920. 



be found a summary of the height, yield, and root development of the cereals 

 at the several stations. The yield is the average of 25 to 30 square-meter 

 quadrats taken from the several plats at the three stations respectively, 

 that from Lincoln being from the lower crop area. All of the crops were 

 assembled in the botanical laboratories of the University of Nebraska and 

 thoroughly air-dried before weighing. A study of the table shows that the 

 crops are progressively shorter from Lincoln westward and that the average 

 yield is also less. The results correlate well with those obtained during 1919, 

 when data from a large number of fields in the different grassland associa- 

 tions were obtained (Weaver, 1920 : 123). 



Regarding weight of threshed grain, Lincoln is highest in every case, and 

 Burlington second except in the case of oats. The low yield at PhilUps- 

 burg was due in part to the rust epidemic. 



Root development, as regards both working depth and maximum extent, 

 is greatest in every case (except one) at PhilUpsburg, although these depths 

 average less than those found at Peru during 1919. The shortest roots 

 occurred at Burlington, where the hardpan demarked at once the limit of 

 water penetration and root extent. The greater root extent at Phillipsburg 



