THE WATER IN A SOIL. 73 



ration always takes place, these substances become more 

 concentrated. 



The composition of the water present in a soil can be 

 deduced from analyses of drainage water, though doubtless the 

 former is richer in dissolved substances. 



Many analyses of drainage water have been made at 

 Eothamsted by Warington,* and at Grignon by Deherain. At 

 Eothamsted the average rainfall and drainage through 5 feet of 

 bare soil were as follow : 



Average of 16 years. 18711886. 



Rainfall. Drainage. 



Inches. Inches. 



March ... ... 1-58 -66 



April ... ... 2-32 -75 



May ... ... 2-21 -54 



June ... ... 2-56 -54 



July ... ... 2-88 -61 



August ... ... 2-50 -53 



September ... 2-98 -88 



October ... ... 3'39 1-71 



November ... 3'13 2-09 



December ... 2-55 1-94 



January ... ... 2-69 2-10 



February ... 2-25 1-60 



Total, whole year ...31-04 13-95 



March to September... 17-03 4-51 



October to February... 14-01 9-44 



According to later results at Eothamsted the average for 

 20 years gives rainfall, 30 inches ; drainage from uncropped 

 land, 14 inches. From a soil bearing a vigorous crop the 

 amount of drainage is very much less (not much more than 

 half), especially in summer, when drainage is often entirely 

 suspended, except after very heavy rain. The composition of 

 the drainage water will thus be altered, even if the crop does 

 not actively exert any influence, for the dissolved matter 

 should become more concentrated. But the plant exerts an 

 influence in taking up and retaining much of the dissolved 

 matter in the water, particularly the nitrates. 



* J.C.S. Trans. 1887,500 



