124 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Amount of Water Required by Plants. The amount of water 

 transpired during the growth of a plant may be calculated as parts 

 of water per one part of dry matter of the plant, and may be 

 considered to represent the amount of water required by the 

 plant. This quantity will vary considerably according to the con- 

 ditions surrounding the plant, as we have seen in the preceding 

 paragraphs. An estimate of the amount of water required to 

 produce a given weight of dry matter is, therefore, only approxi- 

 mate. Such an estimate may, however, aid in the consideration 

 of problems relating to the water content of the soil. The figures 

 given in the table were secured in experiments of four 

 investigators. 1 



POUNDS OF WATER EVAPORATED BY THE PI,ANT PER POUND OF 

 DRY MATTER PRODUCED. 



In some of the arid states of the United States, fair crops of 

 wheat are grown with an annual rainfall of 13 to 18 inches, most 

 of which falls in the winter before the growing period of the crop 

 begins. This small quantity of water is effective, partly because 

 the soils are rich in soluble plant food, partly because the saline 

 matter in solution decreases transpiration. 



1 Exp. Sta. Record 4, 532, Rep. Wis. Station, 1894; Jour. Hort. Soc. 

 Eng. , 1850. See also Widstoe, Utah Bui. No. 105 ; Montgomery, Proc. Am. 

 Soc. Agri., 1911, p. 261. 



