Investigations at All Stations. 91 



air-dried the vegetation yielded an average of 196 grams per square meter 

 at Burlington, 306 at Phillipsburg, and 444 at Lincoln. Wheat-grass, during 

 1921, gave an average yield per square meter of 400, 457, and 606 grams respec- 

 tively. These data are typical of those obtained during a series of years 

 (Weaver, 1921). 



Similar relations hold as regards the extent of the roots of native vegetation. 

 The roots of seedUng grasses and certain subdominant herbs penetrate the 

 mellow loess soil at Peru more rapidly and to a greater depth than at Lincoln, 

 while at BurUngton the shallowest root-growth was recorded. Similarly, 

 numerous mature prairie plants were found to penetrate from 2 to 4 feet 

 deeper at Peru than at Lincoln or Phillipsburg. Regarding the normal 

 depth of root penetration in the several plant associations, the following 

 data from "Root development in the grassland formation" are instructive. 

 Of 43 species studied in the prairies of eastern Nebraska, 14 per cent had roots 

 which seldom extended beyond the first 2 feet of soil; 21 per cent were rooted 

 well below 2 feet but seldom below 5 feet; while 65 per cent penetrated to 

 depths greater than 5 feet and sometimes to 12 or even 20 feet. 



Among 36 species excavated in mixed prairie (hard lands) , 1 1 per cent were 

 rather superficially rooted, 45 per cent were of intermediate depth (2 to 5 feet), 

 and 44 per cent had roots which extended well below the fifth foot of soil, 

 many in fact to a depth of 7 to 9 feet. Of these, 71 per cent are well adapted 

 to absorb water even when the surface soil only is moist. 



Of 8 of the most impoitant species of the short-grass plains, all but one are 

 adapted for water absorption in the surface soil. Three are shallow rooted, 

 and only one or two normally extend their roots beyond a depth of 5 feet. 



This increasingly greater root depth as one goes eastward from the short- 

 grass plains into regions where the deep subsoil is constantly moist is in 

 agreement with determinations made on the root depth of cereals at 14 

 stations during 1919. Using root extent in the true prairie as unity, the 

 relative depth in mixed-prairie and short-grass plains was as follows : Working 

 depth of rye, 100 : 92 :69; oats, 100 : 95 :79; winter wheat, 100:93:61. 

 Maximum depth of rye, 100:90:65; oats, 100:94:77; winter wheat 

 100 : 80 : 51. 



From the foregoing data a direct correlation may be seen between the 

 development of the tops and roots of crops and that of the native vegetation 

 growing in the same general environment. 



