Transpiration as a Factor in Crop Production. 
155 
These apparently contradictory and yet very logical water 
relationships may be clearly brought out in Charts XIX and 
XX. 
There is a rather prevalent popular theory that the absorption 
of food materials from the soil is dependent upon the transpira- 
tion rate; that in an infertile soil containing a weak nutrient 
solution, the crop must transpire at a relatively much more 
rapid rate in order to obtain the necessary amount of nutrients; 
that the plant exercises control over this transpiration rate and 
thereby can control the amount of nutrients absorbed; and 
that in a fertile soil containing a strong nutrient solution the 
necessary amount of nutrient materials may be absorbed with a 
relatively small amount of water, thus making it possible for the 
plant to thrive on a much smaller amount of water. Indications 
are, however, that the transpiration rate is independent of the 
strength of the soil solution, and that a more fertile soil does not 
lower the total amount of water necessary for the plant but 
rather increases the production thru increased vigor of growth, 
and thereby coincidentally reduces the amount of water used 
per unit dry matter. 
80 % 
4o% 
i 
i 
1 
i 
I 
/ // 
f 
i 
'%\ 
4 
/// 
'/// 
/brf/fe so// so/7 
Chart XIX. — Effect of manure on the water requirement per unit of dry 
matter with corn. Average of 1911 and 1914. Graph from Table 65. 
