FERTILIZERS. 57 



But need so much of all these ingredients be used ? The crop 

 maj' have the power of making use of the compounds of nitrogen 

 alread}' stored in the soil or supplied by the atmosphere, so that at 

 least a part of the $15.40 worth of nitrogen will be superfluous. 

 The application of g3'psum is often equivalent to the addition of 

 potash, since gypsum tends to liberate this from its combinations 

 in the soil, and thus render it available to plants, and so we may 

 get our potash at a good deal less cost than in the So. 20 worth of 

 potash salts. Or, for that matter, the soil will very likely supply 

 plent}' of potash and we may leave it out of account entirely in our 

 formula. The ph3'sical condition of the soil affects ver}' materiall}' 

 the feeding of plants and the action of fertilizers. For these, and 

 various other reasons which this is not the place to discuss, and 

 which are, in the present state of our knowledge, very imperfectly 

 understood, the formula, however attractive in theory' , might be far 

 from the most economical, in fact. 



One of the chief defects of formulas on this plan is that they take 

 no account of what we may call the feeding capacities of the crops. 

 A vast deal of experience in the laboratory and in the field bears 

 concurrent testimony to the fact, though we know as yet very little 

 about how or why it is so, that different kinds of plants have 

 different capacities for making use of the stores of food that every 

 soil contains. Clover will get plent}' of nitrogen where wheat will 

 fail for lack of it. Nitrogenous manures help clover but little, and 

 are almost a specific for wheat ; and this, notwithstanding clover 

 contains a great deal, and wheat but little nitrogen. Lawes and 

 Gilbert found that a soil -from which a clover crop had just been 

 removed, contained more nitrogen than it did before the clover was 

 put in ; that, in other words, the soil, to the depth of nine inches 

 at least, was positively enriched b}- the growth and removal of a 

 highly nitrogenous (clover) crop. The nitrogen for a clover crop 

 of two tons on this plan would cost perhaps $16. To bu^' and use 

 it — at least so much of it — would be absoluteh' wasteful. 



The analysis of a plant is a ver}' incorrect standard for the fer- 

 tilizer to appl}' to it. The idea of fertilizing on this basis is old, 

 simple, attractive, costly, partly rational, and often profitable. It 

 is a step in advance of the common plan of using fertilizers at ran- 

 dom. But it is uneconomical in the extreme. 



The next step in advance would be to fit the fertilizer to the 

 actual demands of the crops. This may be done by classifying 



