84 MASSACHUSETTS AGRICULTURE. 



ing, and the crop is diminished over what it might be were 

 the conditions reversed. Indeed, Baron Liebig asserts, that 

 a soil must contain at least twenty-five times as much phos- 

 phoric acid as is required by the plant, before we apply the 

 extra amount as a manure for the plant. The nitrogen of 

 barn-yard manure seems to be f:ir less effectual, according to 

 the Rothamsted experiments, than the nitrogen furnished by 

 pure chemicals, and even chemical nitrogen must be applied 

 for at least three times the necessities of the plant ; i. e. , the 

 plant removes but one-third of the applied nitrogen. 



We can usually find more phosphoric acid and more potash 

 in our soils than can possibly be required for the use of one 

 crop, yet despite this, the crops fail. This is, perhaps, the 

 normal condition of our New England cultivated fields. The 

 soluble constituents of fertility are present in the soil in 

 absolutely large amount, but as absolutely in quantities so 

 small compared with the bulk of inert matter, that in a given 

 root-area not enough is afforded to the plant for continuous 

 growth. That the soil should contain fertile elements in large 

 abundance, is necessary for the continuance of a succession of 

 crops, and these considerations may explain why it is more 

 expensive to bring up a "run down" field, than it is to con- 

 tinue it under good culture after it has received condition. 



If, therefore, we should add to a field whose fertile constit- 

 uents arc present, yet too widely distributed for the roots of 

 our plant to collect, the elements necessary for a full crop, 

 and all these elements in such a form and in such a condition 

 that they may be within reach of the plant throughout the 

 season of growth, we should expect results, not accurately 

 representing a balance between fertility supplied and removed, 

 but proportionate to the amount supplied and the fertility 

 already existent, but just below the minimum requisite 

 amount in the soil ; this result only, be it understood, being 

 predicated on known conditions of plant-habit and plant-yield. 

 To illustrate : In the corn plant, the size of ear and the num- 

 ber of ears on a stalk, are largely determined by variety of 

 seed. No matter how much fertility be supplied to a given 

 crop, the yield cannot be proportionately increased beyond 

 this limitation of variety ; for the number of ears cannot be 

 increased, and their size but very slightly, if at all, by an 



