PLANT NUTRITION. 35 



the leaves to take it from the air, and the roots to take from the 

 soil all the carboa that the plant wants. We need not feed plaats 

 with carbon. 



Now we come to the other organic element — nitrogen. This 

 enters largely into the general structure of plants, and is avail- 

 able in Nature only in small quantities. There is plenty of it in 

 the air, yet scientists are agreed that plants get little nitrogen 

 from the air. They get some from it — more from the decompo- 

 sition of organic substances — yet all scientists agree that the 

 farmer must supply nitrogen ; the plant cannot get enough of it, 

 and he may supply it any form he please, provided it is available. 



Turn now to the mineral elements. What will nature do in the 

 way of ash constituents, and what must I do? Now, with a full 

 knowledge of the fact that I may be in error, I say, that on the 

 average of our soils the farmer need never apply lime to feed his 

 plants. I know that you are in the habit of applying lime to your 

 soils ; keep on doing so, you are doing right, but I repeat that on 

 our New England soils the farmer need not apply lime for plant 

 food, except in certain cases, as in the production of tobacco — and 

 the same is true of magnesia. He need never apply soda, he need 

 never apply sulphuric acid, he need never apply chlorine, nature 

 has supplied abundant material to afford all these, save in excep- 

 tional cases. 



There are only two things left. One is potash, the other is 

 phosphoric acid. It is true that all granitic rocks contain more 

 or less potash in their feldspar. Plants take out of the soil so 

 much potash in their structure that the supply that is available in 

 the soil soon becomes exhausted, or nearly so, and of this the 

 minimum quantity will measure the maximum quantity of the 

 crop ; so the farmer is obliged to furnish potash. 



The other element is phosphoric acid. Phosphoric acid exists in 

 the soil in small quantities, obtained from the disintegration of 

 phosphoric rocks. Seed bearing plants, especially, take up large 

 quantities of phosphoric acid, and the consequence is, that it 

 must be applied, for the minimum quantity will measure the maxi- 

 mum quantity of your crops. 



You will bear in mind that I am speaking of feeding plants. I 

 am saying nothing about the construction of the soil ; I am con- 

 structing plants, and for the construction of plants on the average 

 soil of New England it is needful that the farmer shall supply 

 nitrogen of the organic elements, and potash and phosphoric acid 



