446 NATURE AND PROPERTIES OP SOILS 



amount. Typical guano carries uric acid, urates, and am- 

 monium salts. The phosphorus occurs as calcium, potas- 

 sium, and ammonium phosphates. The potash is found in 

 the chloride, sulfate and phosphate forms. While guano 

 was once a very important fertilizer, the deposits are very 

 nearly exhausted and but little now appears on the market. 

 Process fertilizers are obtained by treating organic trade 

 wastes and refuse with acid or with steam under pressure 

 Hydrolysis of the proteins occurs with the formation of pro- 

 teoses, peptones, and simple amino acids. The water soluble 

 nitrogen of such materials has been shown by Lathrop of the 

 United States Bureau of Soils to be as readily available as 

 that of dried blood or tankage. 



These compounds vary greatly in their values as fertilizers. 

 Guano, process goods, and fish scrap when in the soil decom- 

 pose rapidly and are as effective ordinarily as blood or tank- 

 age. Untreated leather meal and wool and hair waste decay 

 very slowly and are of little value as fertilizing materials. 



246. Utilization of nitrogenous organic compounds by 

 plants. — One of the early beliefs in regard to plant nutrition 

 was that organic matter as such is directly absorbed by higher 

 plants. This opinion was afterwards entirely replaced by the 



