COMMERCIAL FERTILIZERS 351 



nitrogen plays a most important part in producing an abun- 

 dance of tender succulent leaves. It is the most expensive 

 element of plant food. 



Nitrogen may be purchased in many forms. Nitrate of 

 soda is used in comparatively small amounts and applied 

 at intervals of ten days to two weeks. If applied all at 

 one time, a large proportion is lost by leaching before the 

 plants are ready to take it up. A common practice is to 

 use a little at the time of planting, followed by other applica- 

 tions as the crop develops. Sulphate of ammonia, not so 

 quickly available, is used to supply nitrogen during a longer 

 season of growth. All the organic forms of nitrogen, as 

 dried blood and tankage, must decay before the nitrogen 

 becomes available. 



Phosphorus. Phosphorus aids in maturing the crop 

 and producing maximum yields. Many soils are lacking 

 in this element. Acid phosphate, bone meal, and raw 

 rock phosphate are common sources of this element. 



Potassium. Sandy soils and muck lands are likely to 

 be low in potassium. Root crops require a bountiful sup- 

 ply of this important substance. Muriate of potash and 

 sulphate of potash are the most common forms used by 

 commercial gardeners. 



The amount of commercial fertilizer that can be profitably 

 used varies from 300 pounds to one or two tons per acre. 

 Where two or more crops are grown annually upon the 

 same land, the commercial grower endeavors to apply a 

 small excess of all the essential fertilizer elements needed 

 by the crops. One ton to the acre for a single crop is 

 considered a liberal application, and it is seldom that 

 larger amounts are profitable. 



Lime. Few crops thrive in sour soils. It is highly 



