[393] SCIENTIFIC MANUAL. 107 



though intended as ' 'complete fertilizers." Others, in re- 

 sponse to a demand for superphosphate for composting 

 with stable manure and cotton seed, have omitted both pot- 

 ash and ammonia, assuming that these latter substances 

 would be sufficiently supplied by material already on the 

 farm. 



Much depends upon the source from which manufac- 

 turers derive the "three elements" of their compounds, as 

 well as upon the forms in which they exist when offered for 

 sale. 



The price of nitrogen is estimated, according to its source, 

 at from 25 cents down to 15 cents per pound, phosphoric 

 acid from 12.5 to 3,5 cents, and potash from 9 to 6 cents 

 per pound. 



Nitrogen is the most costly element which enters into 

 the so-called complete manures. 



The expense of purchasing this, may, to a large extent, 

 be avoided if all of the home manurial resources are hus- 

 banded. 



By a liberal use of pea-vines as a soil fertilizer, and by 

 supplementing the cotton seed and animal manures of the 

 farm with superphosphate containing a small per cent, of 

 potash, lands may be either improved in fertility, or their 

 normal condition maintained with but little expenditure for 

 nitrogen. 



The principal products removed from the farm in Geor- 

 gia, and sent to market, carry off very little plant-food. 



If, therefore, all refuse products are either returned di- 

 rectly to the soil, or fed to animals whose manure, solid 

 and liquid, is applied to the soil, it will require many years, 

 if surface washing is prevented, to become exhausted, even 

 if no artificial fertilizers are used. The true system to be 

 pursued by Georgia farmers is to turn under a crop of pea- 

 vines (or allow them to decay upon the ground) every three 

 or four years; compost with superphosphate, having a small 

 per cent, of potash, all the animal manures and surplus cot- 



