Oct. IS, 1914 Water Requirement of Plants 23 



The least efficient variety tested in the sorghum group is Sudan grass 

 (PI. V, fig. i), a forage plant which has recently received consider- 

 able attention in the southern Great Plains. Only one year's meas- 

 urements are available for Sudan grass, but the results so far indicate 

 that it is not the equal of other well-known varieties of sorghum in 

 efficiency in the use of water. Sudan grass required 40 per cent more 

 water than Brown kaoliang for the production of the first crop. 

 The second crop was light at Akron and had a much higher water require- 

 ment. On the basis of the two cuttings combined, the water require- 

 ment of Sudan grass was 62 per cent higher than Brown kaoliang. As a 

 forage crop, however, the shorter and more slender stalks of Sudan grass 

 may offset the disadvantage of its higher water requirement. 



In the production of grain the Minnesota Amber' variety gave the 

 lowest water requirement ratio so far recorded for a sorghum crop, viz, 

 607 ±15. The Minnesota Amber produced a pound of grain at Akron 

 in 1 91 2 with less water than was required by alfalfa in the production of 

 a pound of hay. The high water requirement for grain production in 

 Red Amber sorghum, Dwarf milo, milo, and White durra (PI. IV, 

 fig. 3) is largely due to an attack of aphids, which caused many of the 

 flowers to fail to produce seed. The parasites were killed by spraying 

 early enough to prevent any serious reduction in total growth. 



The 1 91 3 water requirement measurements of sorghum were confined 

 to two varieties, Red Amber and Minnesota Amber, both of which were 

 included in the 191 2 measurements. The two varieties gave in 191 3 

 practically identical water-requirement ratios — namely, 296 ±1 and 

 298 ±2. The results from individual pots were in excellent agreement 

 as indicated by the small probable error. A similar agreement was 

 observed in 191 2. Each variety in 191 3 showed an increase of 25 per 

 cent in the water requirement as compared with 191 2. 



A series of water-requirement measurements were made at Amarillo, 

 Tex., in 1913, for the purpose of determining the influence of climatic 

 environment on the water requirement. These measurements also 

 included a number of sorghum varieties, the water requirement of which 

 had never before been determined. Plants have a higher water require- 

 ment at Amarillo than at Akron, so that measurements of different 

 plants at the two stations are not directly comparable. The water 

 requirement of Red Amber and Minnesota Amber sorghum was meas- 

 ured at both stations in 1913, and the ratio of these measurements affords 

 a means for reducing the Amarillo values to the basis of the Akron meas- 

 urements. The mean water requirement of these two varieties at Akron 

 was 85 per cent of that at Amarillo. The Amarillo water-requirement 

 measurements as given in Table XVI have been reduced accordingly 



' This variety was represented by a strain selected for its drought resistance by Mr. A. C. Dillman. of the 

 Oflice of Alkali and Drought Resistant Plant Investigations. 



