94 THE SOIL. 



that the diminution in the quantity of potash in the 

 water of the second lysimeter resulted from its absorption 

 by the roots of the barley, we should be necessarily led to 

 infer that the plants received — 



By the agency of tlie percolating water 0'082 grammes 1"3 grs. 

 Direct from the soil . . . 2-151 „ 33-2 „ 



Total . . 2-233 ,, 34-5 „ 



and, accordingly, 96*4 per cent, dii'ect from the soil, and 

 3'6 per cent, from the water ; that is, 27 times more from 

 the former than from the latter. 



Let us now assume, from the results obtained ^vith the 

 third lysimeter, which was filled with earth richly 

 manured with cow-dung, that the rain-water faUing on a 

 surface of one hectare (2^ acres) of land, dissolves, out of 

 a layer of arable sm-face soil 6 inches deep, 12-65 kilo- 

 grammes (27*8 lbs.) of potash ; and let us compare with 

 this the quantity of potash withdrawn fi'om a hectare of 

 ground by a potato or turnip crop. We know that an 

 average potato crop from a hectare contains in the 

 tubers 204 kilogrammes (449 lbs.) of ash, of which 100 

 kilogrammes (220 lbs.) are potash ; and an average 

 turnip crop, 572 kilogrammes (1258 lbs.) of ash, of 

 which 248 kilogrammes (545 lbs.) are potash ; and we 

 easily perceive tliat, even had the entire amount of the 

 potash dissolved by the rain been conveyed into the 

 plants to serve as food, yet this would be sufficient to 

 supply, with the necessary potash, only the eighth part of 

 the potato tubers and the twentieth part of the turnips 

 severally produced on a hectare of land. The amount of 

 potash in the percolated water shows the quantity of 

 potash which the water could possibly absorb ; and as 

 comparatively but a small portion of the percolating 



