44 BULLETIN" 355, U, S. DEPAETMENT OF AGRICULTURE. 



abnormal decomposition takes place, through bacterial action, result- 

 ing in a loss of free nitrogen from the soil. Such an abnormal de- 

 composition is called denitrification. An acid condition of the soil 

 is unfavorable, also, to nitrification. The farmer should recognize 

 that suitable conditions must be provided for normal bacterial growth 

 in the soil if good crops are to be expected. 



Commercial materials containing nitrogen (Ref. No. 1, pp. 190-196; 

 or No. 7, pp. 244-260). — Besides the natural methods discussed 

 above of keeping up the nitrogen supply of the soil, there are many 

 commercial products on the market which are used to a considerable 

 extent for certain soils and crops. These include mineral salts, 

 together with waste products of both animal and vegetable origin. 

 The principal mineral salts of nitrogen used on soils are sodium 

 nitrate and ammonium sulphate, together with calcium cyanamid 

 and calcium nitrate, which have recently been manufactured from 

 atmospheric nitrogen. 



Cottonseed meal is the principal organic source of nitrogen used as a 

 fertilizer in the United States. In fact, it is used to a larger extent 

 in this country than any other kind of nitrogenous fertilizer, notwith- 

 standing the fact that it is also a valuable stock food for which the 

 demand is steadily increasing. 



The commercial animal products used as fertilizer include slaughter- 

 house refuse, especially dried blood and tankage; fish not valuable for 

 human food, which has teen prepared for use as fertilizer by cooking 

 and extraction of oil; bird guanos; and stockyard manure. Peruvian 

 guano formed from the excrement of birds deposited in large quan- 

 tities on islands off the coast of Peru is rich in nitrogen and was once 

 extensively used in this country, but the original deposits are now so 

 nearly exhausted that there is little or none of the material avail- 

 able for export. 



Of the mineral nitrogen salts, ammonium sulphate is used to a con- 

 siderable extent in this country. Its long-continued use has been 

 found to produce unfavorable soil conditions, which, however, are easily 

 corrected by applications of lime. A mineral material largely used 

 to supply nitrogen to soils is sodium nitrate or Chile saltpeter, so- 

 called because it is obtained mainly from the nitrate deposits of Chile. 

 The great advantage of sodium nitrate as a plant food is that it is 

 readily soluble in water and quickly becomes available to growing 

 crops. When applied to a poor soil its effect can usually be quickly 

 seen in the rapid growth and the rich green color which the plants 

 take on. A disadvantage in the use of this material is its tendency 

 to leaph from the soil, as noted in a previous lesson. Sodium nitrate, 

 and other products rich in nitrogen as well, must be applied to the 

 soil with much knowledge and skill if they are to prove profitable. 

 Usually from 100 to 200 pounds per acre of the nitrate is used, and 



