New York Agricultural Experiment Station. 51 



which potash can usually be obtained. It_is the effect of the potash, 

 not otV; the chlorine, that is desired. An excess of compounds of 

 chlorine in soils renders them baiTen. 



Silicon, in the form of silica and silicates, is abundant in all soils, 

 and does need special attention in connection with fertilizers. 



Calcium. — All plants require calcium or, as it is more commonly- 

 called, lime. Most soils appear to contain an inexhaustible supply" 

 of this' element, and only in exceptional cases does it need special 

 attention in connection with furnishing a supply of plant-food. Cal- 

 cium is Tiot, therefore, regai-ded as an essential constituent of a direct 

 fertilizer, but some of its compounds are known to be valuable 

 under certain conditions as indirect fertilizers. 



Potassium. — Experiments show that when potassium (or potash) 

 compounds are lacking in the soil, the plant suffers greatly, though 

 it does notjiecessarily die. The development of the woodv pai'ts 

 of plants and the fleshy portions of fruits seems to be largely 

 dependent on the influence of potassium compounds. As potash is 

 taken up by vegetation, most soils under constant cultivation sooner 

 or later become deficient in potash, and this loss must be supplied 

 by means of fertilizers. Tlierefore, potassium (potash) compounds 

 are regarded as essential constituents of dii-ect fertilizers. 



Sodium in the form of sodium chloride (common salt) is found 

 in small quantities in all soils. While it appears as a regular, though 

 small, constituent of plants, it is generally held that it is not a neces- 

 sary constituent of plant-food, and that the requirements of plants 

 do not call for the addition of sodium compounds to fertilizers. In 

 the case of nitrate of soda, it is not the sodium, but the nitrogen in 

 the form of nitrate, which gives the compound its value as plant- 

 food. It merely happens that the nitrate can be furnished most 

 cheaply in this form. The application of sodium chloride as an 

 indirect fertihzer has been found, under some conditions, to be 

 attended with beneficial results. 



Magnesium is a necessary constituent of plants, but, so far as 

 known, it rarely needs to be added to a soil. There are some mag- 

 nesium compounds existing as impurities in tlie German potash salts, 

 and when these latter are used, some magnesium is added to the soil 

 incidentally. 



Iron, though used by plants in very small quantities, is an essen- 

 tial constituent of plant-food. It is rarely, if ever, absent from 



