its death, leaving them in the surface soil. But even with the best of 

 management there is some plant food leached from the soil. 



However, according to a well known law, Nature allows nothing to 

 be lost, and these leached out materials are, through various agencies, at 

 least partially, made to accumulate in great beds of limestone, phosphatic 

 rock and potash salts. It is these accumulations of past ages that are 

 to-day furnishing the main constituents of fertilizers. Who knows but 

 what the plant food which is being annually leached from our fields will 

 come into use in future ages. 



Losses of Plant Food in Crops. 



But the leaching away of plant food is not the only way in which 

 these materials are lost from the soil. The vegetable and animal produce 

 of the land are frequently consumed off the land which reared them. A 

 partial return of the plant food thus taken from the soil is made by the 

 application of farmyard manures, but the sale of vegetables, fruit, grain, 

 animals, and animal products, the congregating of men in towns and 

 cities, and the difficulty in employing sewage with profit; and the loss 

 of fertilizing constituents from farmyard manure before it is applied to 

 the land, all tend to make the return of the manurial constituents to the 

 soil incomplete. 



Some soils are naturally so rich in the elements of plant food that 

 when the crops are properly rotated and "catch" crops used to economize 

 this natural wealth of fertilizing constituents, it may be a long time 

 before the soil needs special manures ; but, if the land is naturally poor, 

 or injudiciously cultivated, or if special crops of like nature have to be 

 grown year after year on the same ground, it may soon need some extra 

 manure. 



On naturally poor soils it may be necessary to make a complete return 

 of all the elements of plant food removed by crops ; but in most soils there 

 is an abundance of some one or more of these elements, and a partial 

 manuring will consequently suffice. With intensive farming, where 

 thorough cultivation is practised, a good system of rotation followed, 

 where little grain is sold and some food is purchased in its place, and 

 every care taken of the manure, the land may even gain in fertility. These, 

 however, are not the conditions which exist with the gardener and fruit 

 grower, and they must of necessity purchase manure of some kind. 



FERTILIZERS. 



For the purpose of the present discussion, fertilizers may be divided 

 into two groups. First, those which do not furnish in themselves any 

 needed plant food, but whose chief value depends upon the power they 



