126 



Plant Physiology 



water supplied and the resulting yield, but also the pro- 

 tein and ash content of the grain and the total amount 

 of these components (protein as N) taken from the soil. 

 From the preceding table it is evident that, in general, 



FIG. 40. Springs and reservoir for irrigation of date-palms, Figuig, 



Morocco. 



irrigation water up to thirty acre inches increased the yield 

 of grain and diminished the nitrogen content. The effect 

 of an increase of over thirty inches of water is greatly to 

 diminish the yield; but the percentage, the composition, 

 and the total removal of soil constituents per acre remain 



