116 



MASSACHUSETTS HORTICULTURAL SOCIETY. 



soils. It seldom becomes exhausted, and while it is possible, and 

 doubtless true of some lands, that they are deficient in lime, yet 

 it is probably also true that the greater part of New England is 

 well supplied with this form of plant food. Lime maj', however, 

 act as a fertilizer on soils which, in themselves, are well charged, 

 and it seems certain that a part of the beneficial effects of liming 

 land are due to its indirect action on the soil, b}- which some of 

 the unavailable parts of the soil are rendered available. 



Soda is not regarded as a necessary constituent of plants 

 though it is usuallj^ present. 



Potash is not only essential, but is lacking in many soils that 

 have been cropped for a long time. Phosphoric acid, too, is 

 equally important and probably about equally deficient in soils, — 

 that is, in an available form. 



"Deficient Plant Food" Removed bt Various Crops. 



The above table shows what various common crops remove 

 from the soil, — that is, the parts which we have to consider, 

 when fertilizing to prevent exhaustion or to restore fertility, 

 namely ; Nitrogen, Phosphoric Acid, and Potash. The experience 

 of farmers and the experiments of scientists lead us to the same gen- 

 eral conclusion, namely: that these three substances are the ones 

 that become exhausted when soils once profitable become so far 

 reduced in producing capacity that they no longer pay. 



