Amount of Water Used by Plants 89 



VARIATIONS IN THE AMOUNT OF WATER USED 

 BY PLANTS 



It is a matter of very fundamental importance to know what 

 factors or conditions may cause a variation in the amount of water 

 which is necessary to produce a ton of dry matter, because it is 

 only by knowing these that it will be possible to lay down any 

 general principles for determining the amount of water which 

 will be required to produce a given yield. 



If we examine the data which have been presented, it will 

 be observed that not only is there a rather wide variation in the 

 amount of water used by different crops, but, also, that there is, 

 further, a wide difference recorded as occurring with the same 

 species or variety, sometimes with the same species in the same 

 year, and sometimes for different years, and it is important to 

 know to what these differences are due. 



In the case of corn, for example, where we have grown it 

 under the cylinder conditions in the field, the following varia- 

 tions have been noted: 



In 1891, Pride of the North dent corn used in one case 295.95 

 pounds of water for a pound of dry matter, and in the other 307.03 

 pounds. But in the first case more dry matter was produced by 

 the individual plants, the first producing 4.369 per cent more than 

 the other did, but in doing this only .602 per cent more water 

 was taken ; that is, the most vigorous plants have produced the 

 most dry matter when measured by the amount of water used. 

 Indeed, it may be laid down as a general rule, that the more 

 favorable all conditions are for plant growth, the more effective 

 will be the water supplied to the crop. Good management, there- 

 fore, will look closely to all details, even to the minor ones, 

 for everything counts in plant feeding just as it does in animal 

 feeding. 



Not all varieties of the same species of plant use water in 

 the production of dry matter with the same degree of effective- 

 ness. In our work with dent and flint corn, for example, we have 

 found, as a mean of four trials, that Pride of the North dent 



