218 THE WASTE AND CONSERVATION OF PLANT FOOD. 



loss of iiitroi>cii ])er acre. Tliose crops which require an immense 

 ainoniit of moisture for their growth, such as tlie sugar beet, would 

 tend tliereby to i)revent the loss of nitrogen in the drainage waters, the 

 nitrates being stored in the beet instead of being* given up to i^ercola- 

 tion. In general, it may be said tliat it is the (juantity of the drainage 

 water rather than its richness in nitrates wliicli determines the total 

 loss due to ])ercolatiou, and from this it may be inferred that the loss 

 by drainage is directly proportional to the rainfall and inversely pro- 

 l^ortional to the magnitude of the harvest. The season at which the 

 greatest loss takes j)la(*e is also, therefore, the one in which the growth 

 of the ]»lant is tlu' least vigorous, ])rovided that the vigor of nitritica- 

 tion and quantity of rainfall remain the same. When ]>lants grow 

 vigorously and when tliey occui)y the soil for a long time, the losses 

 due to drainagii are reduced to a mininuim. On the other hand, with 

 plants wiiich rapidly ripen, so that the harvest follows soon after the 

 sowing, the losses are greater. Tlie farmer, therefore, who suffers a fail- 

 ure of his crop, not only loses from the smallness of the harvest, but 

 also by the percolation of the water throiigh the soil. For this reason 

 it is obvious that leaving fields fallow is a very dangerous proceeding. 

 Deherain found that fallow fields during- tlie season lost as high as 50 

 kilograms of nitrogen x>er hectare, corresponding to 330 kilograms of 

 nitrate of soda, worth 70 francs. These figures show jilainly the mag- 

 nitude of the losses which take place in the one item of nitrogen alone, 

 due to the percolation of rain water through the soil. 



In this connection it may be of interest again to refer to the favorable 

 action of lime in a great many soils in regard to its power of increas- 

 ing the ability of a soil to hold the soluble plant foods against their 

 removal by water. This favorable action is particularly manifested in 

 many soils in the power of lime to increase their capacity for holding 

 potash. 



Warington explains this action of the lime salts, especially the car- 

 bonate, by suggesting that by combining with the acids of certain salts, 

 as the carbonates, sulphates, chlorides, and nitrates, they allow the 

 bases of these salts to unite with the hydrated metallic oxides. The 

 carbonate of lime also converts the soluble acid phosphates, applied in 

 manure, to the sparingly soluble calcium phosphates, which, as they 

 gradually enter into solution, are converted into ferric and aluminic 

 phosphates. An admirable description of the absorptive power of soils 

 has been given by Warington,^ and many other authors have also dis- 

 cussed this matter in detail. 



We can see from the data given above how" water continually acts 

 upon a soil in the removal of certain soluble plant foods. It might be 

 inferred from this that all arable soils exposed continually to rains 

 would soon be exhausted of all valuable soluble plant food. But it has 

 also been iiointed out how certain constituents of the soil have a faculty 



' Practice with Science, page 2. 



