Water Needed for a Given Crop 97 



Table showing the least amount of water required to produce different yields of 

 wheat per acre when the ratio of grain to straw is 11.5 



-Yield pei- acre- 



Wgt. of grain Wgt. of straw Total wgt. Water used 



No. bushels TONS TONS TONS ACRE-IN. 



15 .45 .675 1.125 4.498 



20 .6 .9 1.5 5.998 



25 .75 1.125 1.875 7.497 



30 .9 1.35 2.25 8.997 



35 1.05 1.575 2.625 10.495 



40 1.2 1.8 3 12 



These amounts of water, given in the last column 

 of the table, are so small that they appear false, for the 

 quantity given for 15 bushels to the acre is almost 

 covered by the rainfall of the most arid parts of the 

 world. Several statements need to be made in order 

 to put them in their true light. 



In the first place, the figures could only be true 

 when the amount and kind of plant -food in the soil 

 is all that the crop can use to advantage, for no amount 

 of pure water can make up for such deficiencies except 

 in so far as it makes more rapid the solution of other- 

 wise unavailable plant -food in the soil. Then, again, 

 the data for the table were procured under conditions 

 which permitted no loss of moisture from the soil, 

 either by surface drainage or by downward movements 

 beyond the depth of root action. Further than this, 

 no account is taken of the water which may have been 

 given to the soil in bringing it to the proper moisture 

 conditions previous to planting the crop in it. Water 

 enough was given to the soil to put it in the right 

 condition to start with, and the amounts in the table 



