246 THE FARMER OF TO-MORROW 



much immediate importance to the plant as 

 the water that comes up the capillary water. 

 Gravitational water passes quickly through a 

 well-drained friable soil, seeking the water 

 level below. This may be a matter of inches 

 or feet, according to the nature of the par- 

 ticular soil. After a heavy rainstorm the 

 drains are filled not by water from above, 

 but by the rising of the so-called water-table 

 from below. 



Drain waters for this reason contain, as a 

 rule, much less "plant food" than do capillary 

 waters, having remained in contact with the 

 soil for only a brief period. Yet, if one ad- 

 heres to the theory that the mineral resources 

 of the soils are so limited in quantity as to 

 be exhaustible in the history of man on earth, 

 he must also subscribe to the belief that the 

 loss from leaching through drainage is in time 

 enormous. We have already quoted an esti- 

 mate as to the amount of fertility lost in this 

 way potassium, 51 pounds; magnesium, 16 

 pounds; calcium, 5 pounds, and phosphorus, 

 42 pounds per acre in four years' time. Ac- 

 cording to many estimates, these quantities 

 are sufficient to grow a crop ; and, thus, every 

 fourth year the equivalent of five crops have 



