320 



MICROBIOLOGY OF SOIL 



limed the humic acids and acid humates are changed into neutral com- 

 pounds and are then subject to more rapid decomposition by micro- 

 organisms. According to the investigations of Blair the average acid 

 soil in Florida requires 1,500 pounds of lime (CaO) per acre to neutralize 

 the acidity to a depth of 84 mm. (9 inches). This means an acidity 

 equivalent to more than one ton of hydrochloric acid per acre. In 

 peat and muck soils the acidity is equivalent to many times this 

 amount of hydrochloric acid. 



Protein Bodies 



Amount and Quality. — ^The protein content of farm crops that 

 leave residues in the soil is variable, but in all cases quite considerable. 

 Dried corn stalks contain 5 per cent of protein, timothy hay 6 per cent, 

 red clover hay 12 per cent or more, alfalfa hay 15 or 16 per cent. Even 

 wheat and rye straw may contain as much as 3 per cent of protein. 

 Cotton-seed meal and other oil cakes, tankage, ground fish, hair and 

 wool waste and dried blood (all used more or less extensively as sources 

 of nitrogen to crops) are made up in a large measure of protein 

 compounds. 



Being derived from plant residues, from microorganic, insect and 

 animal remains, and from fertilizers and manures applied, the nitrogen 

 in the soil humus exists, for the most part, in the form of protein com- 

 pounds. Hilgard reports the following humus and nitrogen content, 

 as based on the analyses of a large number of samples of humid, 

 semi-arid and arid soils. 



(Humus), 

 per cent 



(Nitrogen in 

 humus), 

 per cent 



(Nitrogen in 



soil), 



per cent 



Arid uplands 



Sub-irrigated arid soils 



Humid soils from humid and arid regions 



(California) 



Humid soils from other states 



0.91 

 1 .06 



2 -45 

 7.01 



15-23 

 8.38 



S-29 

 3.78 



0-I3S 

 o.ogg 



013s 

 0.29s 



Taking the weight of an acre-foot of dry soil at 2,000,000 kg. 

 (4,000,000 pounds) and multiplying the nitrogen by 6.25 (the factor 

 usually employed for converting nitrogen into protein) we find the 

 protein content of thpse soils to range from about 11,339 ^Z- (25,000 



