80 BOARD OF AGRICULTURE. 



the minutest quantities. It is very rare to detect it in waters, 

 except those which have passed through a very heavily ma- 

 nured soil, or unless it is otherwise especially abundant. Pot- 

 ash, for another example, rarely wastes from the soil, unless 

 it is from light, coarse, sandy land, having but little fine ma- 

 terial in its tilth. 



If the substances which feed the crop, one or all, have be- 

 come reduced in quantity or are not in proper condition as to 

 solubility, we may remedy the exhaustion either by applying 

 the materials in the form of some fertilizer which contains 

 them, or we may omit that, and rely upon those processes 

 by which the original rocks of the earth's surface have been 

 converted into nutritive soil ; the processes by which those 

 substances, once totally unavailable for crops, have been made 

 available. We can wait the operation of the natural agencies 

 which are involved in what we call " weathering;" the action 

 of water, and of the carbonic acid and oxygen in the air. 

 When we leave land in fallow — a thing which is practiced 

 much less now than formerly — these processes go on in the 

 soil, and prepare a quantity of plant-food for the crop of an- 

 other year. This " weathering" process is in constant pro- 

 gress and is of great importance in supplying the materials 

 which our crops demand. If that process should be sus- 

 pended, farming would become a very difficult business. That 

 certain fields will produce crops of the same kind for years 

 and years without any fertilizing adiition whatever, is due to 

 the fact, that as fast as the crop requires and removes the 

 materials given in our table they are supplied by the soil itself; 

 they exist in the soil, were originally stored up there, and 

 they are made soluble day by day, as the crop may need. The 

 rate at which this weathering process goes on determines, 

 other things being equal, the natural yield in a given case. 

 By active tillage, throwing up the soil, so that it is exposed 

 more fully to the air, and by drainage, if this be necessary to 

 ensure access of the atmosphere, this process can be hastened. 

 Most saline fertilizers, such as common salt, nitrate of soda, 

 superphosphate of lime, and plaster of Paris, also act in a 

 similar way to dissolve the elements of the soil, and thus pre- 



