20 



BULLETIN 981, U. S. DEPARTMENT OF AGRICULTURE. 



crops reported to have grown without rain are usually found to have 

 used soil moisture previously stored or to have been favored by the 

 natural run-off from adjoining areas. 



Sudan grass has sometimes given good returns under dry farming 

 in the Southwest at places where the normal annual rainfall is but 8 

 to 15 inches. It yields much more, however, in the southern Great 

 Plains area, where the annual rainfall is between 20 and 30 inches. 

 Growth is abundant in the Southeast, where the rainfall is 40 to 60 

 inches, but this humidity permits the sorghum midge to thrive, which, 

 as explained elsewhere, prevents seed production. Where the rain- 

 fall is about 60 inches and the altitude mostly below 100 feet, as in 

 Florida and other Gulf and Atlantic coast points, Sudan grass pro- 

 duction is usually not profitable, owing to the disease known as red- 

 spot, or sorghum blight. Heavy rainfall, in addition to cold, accounts 

 for the failure of Sudan grass reported within 10 or 20 miles of the 

 Pacific coast in northern California and Oregon. The crop has shown 

 ability, however, to survive inundation for several days as well as 

 corn or any of the sorghums if the soil is drained well. 



Table I. — The water requirements of Sudan grass and other staple crops, as determined 

 by experiments at Garden City, Kans., and Akron, Colo. 



[The data under " Ratio'' show the number of pounds of water required to produce 1 pound of dry matter.] 



Crop plant. 



At Garden City, Kans., 1915 (16, pp. 483-484). 



At Akron, Colo., 1912 (4, pp. 

 50-51). 





Varieties. 



Period of growth. 



Ratio. 



Varieties. 



Ratio. 





Pride of Saline 



Dwarf Blackhull 



May 22 to Aug. 25... 

 May 22 to Sept. 11... 

 May 22 to Sept. 3.... 



267 ± 2 

 221 ± 2 

 244± 3 



Average of 8 



Blackhull 



286 



Kafir 



259±5 



Milo 



Dwarf 



273 ±4 







/Minnesota Amber. . . 

 \Red Amber 



239±2 











237±4 



Millet 





248±7 







May 22 to Sept. 6.... 

 May 22 to Sept. 14... 



249 ± 2 

 306 ±15 



\Kursk 



187 ±2 















359 ±2 











The water requirements of Sudan grass and several other crops 

 were determined on the basis of the total dry matter, exclusive of that 

 in the roots, by Briggs and Shantz in 1912 at Akron, Colo., and by 

 Miller in 1915 at Garden City, Kans., as shown in Table I. These 

 results indicate in a general way that Sudan grass uses more water 

 in the production of a pound of dry matter when the supply of soil 

 moisture is abundant than the other sorghums, the millets, or corn. 

 In the tests at Garden City, Kans., and Akron, Colo., the plants 

 were grown under optimum soil-moisture conditions; that is, the soil 

 was supplied regularly with all the water the plant could use. This 

 condition, of course, did not simulate in the least degree the soil 

 conditions ordinarily found in a semiarid region, where drought 

 endurance is an important factor in crop production. It is impossible 



