AGRICULTURAL TEXT-BOOK. 



35 



available for a growing crop, yet by means of rest, by the action of car 

 bonic acid, and of the atmosphere, or by fullomng, and by the appl ca- 

 tion of chemical or dissolving manures, they may, to a certain extent, be 

 rendered soluble in water, and the producing power of the soil be restor 

 ed. Thus, shut up, there are materials enough to grow twice the amount 

 of crops already taken fiom the land. The third table gives the inor 

 ganic constituents, which are not soluble by any available means ; and 

 therefore they must be considered only as the basis for the others. 



Another fact to be observed is the very small proportion of such con 

 stituents available at any one time for the growth of plants ; and the 

 facility with which soils may be impoverished. In each 100 Ibs. of the 

 soil, free from moisture, only about 2 Ibs. can be converted into vegeta 

 tion. 



This table will be again referred when we coma to consider the sub 

 ject of manures : but it is necessary to remark that, in actual growth, a 

 plant may receive more than the above of necessary nutrition by means 

 of water evaporating from below. ($111.) 



114. III. Fertile pasture soil (A), 

 or unfruitful soil (C). (Johnston.) 



Silica, Quartz, Sand, and Silicates, 



Alumina, ... 



Oxides of iron, 



Oxide of Manganese, 



Lime, - 



Magnesia, ... 



Potash and Soda, 



Phosphoric acid, - 



Sulphuric ncid, 



Chlorine, 



Humicacid, - 



Insoluble humus, 



Organic matter, containing nitrogen, 



Water, .... 



Carbonic acid united to the lime, 



Fertile arable soil (B). Barren 



0.080 



trace 



The first is from a fertile alluvial district of Hanover, from the banks 

 of the West-r ; the second, from the banks of the Ohio River, is celebra 

 ted for yielding successive crops of corn for a long period without ma 

 nure : and the third is from a moor in East Freisland. 



