Investigations at Lincoln, Nebraska. 



55 



tip. Nodules occurred to depths of over 3.5 feet. Little difference was noted 

 in the number or length of branches of roots excavated in the lowland. 



A final examination in the upland plats was made on August 10. At this 

 time the tallest plants were 1.5 feet high, while the crop averaged 1.3 feet. 

 Growth conditions had continued favorable, soil-moisture was abundant, 

 especially in the deeper layers, and root growth continued. Many of the 

 roots had reached a depth of 5 feet, while some penetrated 2 to 6 inches 

 deeper. The tap continued to assume the dominant role, and no change 

 occurred in branching habit. The older laterals were longer and extended 

 laterally often more or less parallel with the soil-surface for distances of 6 to 

 10 inches or turned obliquely downward, usually making wide angles with 

 the tap (fig. 25 a). Root development in both upland and lowland areas 

 during 1919 was very similar to that just described (Weaver, 1920 : 127). 



Sweet Clover, Melilotus alba. 



This crop was planted on the same day as alfalfa (March 31) in level plats 

 adjoining those of the cereals. On May 1, when the plants had reached a 

 maximum height of 0.5 inch, the root systems were examined. None of the 

 roots reached depths greater than 3 or 4 inches. 



A second examination was made on June 2, when the crop was 1.5 to 2 

 inches tall. Many roots extended to depths of 0.9 to 1.2 feet and a few 

 reached the 1.4-foot level. Secondary laterals were fairly abundant, as were 

 also the bacterial nodules. The branching habit was very similar to that of 

 alfalfa of the same age (cf. figs. 24 a and 24 b). 



On July 24, when the crop had reached an average height of about 1.3 

 feet, root development was again examined. Roots were abundant to the 

 5-foot level, while some penetrated the moist soil to a distance of 5.5 feet. 

 On the lowland, where the tops were better developed (average height about 

 2.2 feet) the root development was almost identical as regards depth of pene- 

 tration, abundance of branching and lateral spread, and presence of nodules 

 at all depths. The strong tap-roots varied from 4 to 6 mm. in diameter, 

 penetrated almost vertically downward, and tapered rapidly. Ma j or branches 

 were few, usually only 1 to 3 per plant. These originated at various depths, 

 sometimes near the surface and again as deep as 2 or 3 feet. Like the main 

 root, these larger branches, sometimes 2 or 3 feet long, were furnished with 

 rather numerous relatively short and mostly poorly branched sublaterals. 

 The most marked development of laterals on the tap occurred in the surface 

 foot of soil. No branches extended to horizontal distances greater than 8 

 or 10 inches from the tap and most of them were very much shorter (fig. 25 b). 



Comparison of Root Systems. 



Just as the native species examined in the prairies at Peru were found to 

 be more deeply rooted than those at Lincoln (Weaver, 1919 : 15), so too the 

 crop plants show clearly this difference in root habit. Table 12 summarizes 

 the development of the crops at Lincoln. When this is compared with a 

 similar summary for the Peru crops (table 1), striking differences are at once 

 apparent. Oats at Peru reached a maximum depth of 6.7 feet, at Lincoln 

 only 4.2 feet. The maximum lateral spread was 1.4 feet at the former sta- 

 tion and only 0.8 foot at the latter. Differences in the root development of 



