WATER OF SOIL IN ITS BJSLATION TO PLANTS 249 



greater is likely to be the wind velocity. All this would 

 tend to raise the transpiration ratio. 



171. Effect of soil moisture on transpiration. — From 

 the soil standpoint, however, the factors inherent in the 

 soil itself are of more vital importance as regards 'tran- 

 spiration, since they can be controlled to a certain extent 

 under field conditions. An increase in the moisture con- 

 tent of a soil usually results in an increased transpiration 

 ratio. The work of HellriegeP with barley grown in 

 quartz sand containing a nutrient solution may be cited 

 in this regard, together with the data obtained by Mont- 

 gomery^ at Lincoln, Nebraska, with corn grown in a 

 loam soil : — 



EFrccT OF Soil Moisture on Transpiration 



Barley — Hellriegel 



Corn — Montgomery 



Soil Moisture Per- 

 centage of Total 

 Capacity 



Transpiration 

 Ratio 



Soil Moisture Per- 

 centage of Total 

 Capacity 



Transpiration 

 liatio 



80 

 60 

 40 

 30 

 20 

 10 



277 

 240 

 216 

 223 

 168 

 180 



100 



80 



60 



45 



35 



290 

 262 

 239 

 229 

 252 



These data show clearly that an excessive amount of 

 water in the soil is not a favorable condition for the 



^Hellriegel, H. Beitrage zu den NatunvissensehaftlicliGn 

 Grundlagen des Aekerbaus, Seite 639. Braunschweig. 1883. 



2 Montgomery, E. G, Methods of Determining the Water 

 Requirements of Crops. Proe. Amer. Soe. Agron., Vol. 3, 

 p. 276. 1911, 



