318 HOW CROPS FEED. 



1,500 tons must remain to give to the plant all that it liolds 

 in solution. These 1,500 tons of water must, if they have 

 the same composition as that which escapes, contain only- 

 two and a lialf pounds of potash and less than a pound 

 of ammonia. It may be alleged that the water which re- 

 mains lying longer in contact with the soil may contain a 

 larger quantity of matters in solution ; but even admit- 

 ting this to be the case, it cannot for a moment be sup- 

 posed that they can ever amount to more than a very 

 small fraction of what is required for a single crop." 



The objection to this conclusion which Anderson al- 

 ludes to above, but which he considers to be of little mo- 

 ment, is, perhaps, a serious one. The soil is saturated 

 with water sufficiently to cause a flow from drains at a 

 depth of 4 to 5 ft., for but a small part of the grow- 

 ing season. The Indian corn crop, for example, is planted 

 in New England in the early part of June, and is harvest- 

 ed the first of October. During the four months of its 

 growth, the average rain-fall is not enough to make a flow 

 from drains for more, perliaps, than one day in seven. 

 During six-sevenths of the time, then, there is a current of 

 water ascending in the soil to supply the loss by evapora- 

 tion at the surface. In this way the solution at the sur- 

 face is concentrated by the carrying upward of dissolved 

 matters. A heavy rain dilutes this solution, not having 

 time to saturate itself before reaching the drains. Ac- 

 cordingly we find that the quantity of matters dissolved 

 by water acting thoroughly on the surface soil is greater 

 than that washed out by an equal .amount of drain-water ; 

 at least such is the conclusion to be gathered from the 

 experiments of Eichhorn and Wunder. 



These chemists have examined the solution obtained by 

 leaving soil in contact with Just sufficient water to saturate 

 it for a number of days or weeks. ( Vs. St., II, pp. 107- 

 111.) 



The soil examined by Eichhorn was from a garden near 



