THE ROOT SYSTEMS OF CEREALS. 121 



4.6 feet depth. The wheat roots had a working depth of 3.2 feet, a few 

 extending 0.5 foot deeper. 



In an adjacent field a crop of rye had been grown. It had been 

 drilled in the corn at the rate of 2 bushels per acre on September 1 . It 

 had a great abundance of straw, which averaged 4.2 feet in height, but 

 the heads did not fill out well. As in all of these fields, the dry surface 

 soil was very hard and filled with cracks often half an inch wide. These 

 were especially pronounced in the rye. However, at 0.7 foot depth the 

 soil became moist, and this condition prevailed through the "hardpan" 

 at 3.5 feet and to all depths examined. The soil was similar to but less 

 clayey than that in the wheat. The working depth of the rye roots 

 was 3.8 feet, although some extended 0.8 foot deeper. 



SUMMARY. 



For comparison these data on root development and height growth of 

 the cereal crops are summarized in table 10. A statement of grain 

 yield would also have been very desirable had it not involved either 

 an amount of work incommensurate with its value or the inclusion 

 of data furnished by a number of farmers and ranchmen. More- 

 over, as is well known, local conditions at the time of blossoming or 

 when the grain is maturing often materially affect, if indeed they do 

 not largely determine the yield. Undoubtedly the vegetative develop- 

 ment is the best criterion for our purpose. 



A study of table 10, which records the development of rye, shows 

 striking relationship between the growth of the crop and the degree of 

 xerophytism of the plant association. Not only the height of tops and 

 the working depth of the roots, but also the maximum root-depth, in- 

 creases consistently from short-grass plains through mixed prairie to 

 true prairie. In fact, this was found to be the case with oats and also 

 with wheat. Except for the greater development of both roots and 

 tops at Burlington (a phenomenon which is clearly related to an unusual 

 local moisture-supply) the averages for rye would have been much less 

 in short-grass plains. Through this association the maximum root 

 penetration, not only for rye but also for the other cereals, is clearly 

 related to the depth of water penetration. The root penetration in 

 mixed prairie in all three soil types was markedly greater than in 

 short-grass plains. Likewise, the height of tops, with the exception 

 of the crop grown in pure sand, and the working root depth were 

 greater in every instance but one in true-prairie soils than was the 

 average development under mixed-prairie environment. 



Using oats as the indicator, the average differences are just as con- 

 sistent even if not so great. The shorter growing period of this crop 

 probably accounts for these smaller differences. Here, again, the 

 averages of root depth in short-grass plains are increased by the greater 

 root penetration at Burlington. 



