CHAPTER VI 



THE WATER REQUIREMENTS OF CROPS 

 AND OF VEGETATION 



FROM what has been said respecting the use of water by 

 plants, more especially transpiration, it is obvious that 

 the requirements of vegetation and of crops will be most 

 diverse, and that any particular crop or type of vegeta- 

 tion will show a modified use dependent upon temperature, 

 light intensity, strength of soil solution, texture of soil, 

 and the like. 



66. Relative requirements of a few crops. Lyon and 

 Fippin have compiled a statement of the water needs of 

 several crops which is suggestive. These crops were tested 

 by the different observers under dissimilar conditions, and 

 close agreement is not to be expected. Moreover, the 

 methods of controlling or estimating the evaporation of 

 water from the surface of the soil has not been the same 

 with the different observers, and this might easily lead to 

 important differences. See table on opposite page. 



Taking 300 pounds of water as an average amount 

 transpired by crop plants, in order to produce 1 pound of 

 dry matter under conditions in England, Hall has prepared 

 a table giving the precipitation necessary to supply the 

 water used by certain crops. For conditions in the central 



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