MATTERS DISSOLVED BY BAIN WATER IN SOIL. 101 



grains). The difference is 0'082 gramme (1'3 grains). 

 f we think ourselves warranted in concluding "from 

 this, that the diminution in the quantity of potash in 

 the water of the second lysimeter resulted from its ab- 

 sorption by the roots of the barley, we should be neces- 

 sarily led to infer that the plants received 



By the agency of the 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, direct 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 with 

 the third lysimeter, which was filled with earth richly 

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

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

 of a layer of arable surface soil 6 inches deep, 12-65 

 kilogrammes (27'8 Ibs.) of potash ; and let us compare 

 with this the quantity of potash withdrawn from a hec- 

 tare 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 Ibs.) of ash, of which 

 100 kilogrammes (220 Ibs.) are potash ; and an average 

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

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

 easily perceive that, 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 tur- 

 nips 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 ab- 

 sorb ; and as comparatively but a small portion of the 

 percolating water comes in contact with the roots of 

 the plants, and can give up potash to them, it is clear 

 that the constituents of the solution moving about in 

 the soil have but a very trifling share in the process of 

 nutrition, while the absence from it of ammonia and 



