376 FIELD CROPS FOR THE COTTON-BELT 



464. Drought resistance, — The peculiar adaptation 

 of the sorghums, particularly the grain-sorghums, to 

 agriculture in semi-arid regions, is well known. As to 

 those qualities or factors that enable the sorghums to 

 successfully resist dry, hot weather, our knowledge is less 

 clear. These qualities cannot be attributed to the exten- 

 siveness or depth of the root-system as we have already 

 seen that the root-system of sorghum is less extensive than 

 corn, a crop not particularly adapted to dry regions. 

 Observations also indicate that- as much water is required 

 to produce a pound of dry matter in sorghum as in corn. 

 It would therefore seem that the rather prevalent belief 

 in the exceptionally low water requirement of sorghum is 

 not tenable. The most probable explanation of the pecul- 

 iar adaptability of the sorghums to dry, hot regions is to be 

 found (1) in the high degree of resistance of the sorghum 

 plant to injury from dry, hot weather and (2) the ability of 

 the sorghum plant to cease growing and become prac- 

 tically dormant during periods of severe drought, growth 

 being renewed without any apparent injury with the 

 coming of rain. 



465. Effects on the soil. — The sorghums, particu- 

 larly the saccharine varieties, are generally considered to be 

 hard on the land. The reasons for this are not clear. 

 Among the explanations so far advanced the following 

 seem to be the most reasonable: (1) The sorghums seem 

 to concentrate their feeding roots in the upper layers of 

 soil to a greater degree than most other crops, which 

 peculiarity probably results in exhausting the surface soil 

 of its available fertility. (2) Sorghum stubble often breaks 

 up cloddy on account of the fact that the soil is held to- 

 gether by the matted roots. (3) The slowness with which 

 sorghum stubble decays renders its immediate effects less 



