DECOMPOSITION OF ORGANIC MATTER IN THE SOIL. 261 



The influence of temperature on nitrate formation has been observed 

 by many investigators. Already Schloesing and Miintz recorded that 

 at 5 nitrification is quite feeble, at 12 marked and at 37 at its best. 

 Other investigators have obtained substantially the same results, except 

 that the optimum has been found to be considerably lower, often between 

 25 and 30. Under field conditions nitrification seems to take place at 

 relatively low temperatures, as is indicated by the rapid oxidation of 

 ammonium salts in the Rothamsted experiments in England; and the rapid 

 decay and nitrification of clover and of other legume residues in the 

 experiments at the New Jersey Experiment Station. These facts have, 

 therefore, an important bearing on the nitrogen feeding of crops in tropical, 

 subtropical and temperate zones. 



The influence of lime and of other basic substances including the 

 carbonates of magnesium, potassium and sodium, and of the oxides of 

 iron is of far-reaching importance in all nitrification processes. It is 

 well known that applications of magnesian and non-magnesian lime, 

 marl or wood ashes promote nitrification in the soil and in compost 

 heaps, a fact that was well recognized by the ancient niter refiners. The 

 favorable action of lime is readily explained by its ability to neutralise 

 organic and mineral acids and to render, thereby, the soil reaction 

 favorable for the rapid growth of ammonifying, as well as of nitrifying 

 bacteria. Furthermore, the reserve of basic material serves to neutralize 

 the acid formed by the bacteria and prevents thus the accumulation of an 

 undue amount of acidity. 



The role of certain mineral salts in promoting nitrification is quite 

 significant. Small amounts of sodium chloride have been found to favor 

 nitrification in the experiments of Pichard and also those of Lipman. 

 The former showed also that sulphates not only promote nitrification, 

 but that different sulphates display marked variations in this respect. 

 In the same manner nitrate formation was shown to be favorably affected 

 by phosphates in bone meal, Thomas slag, and acid phosphates. Gener- 

 ally speaking, therefore, nitrifying bacteria are stimulated in their de- 

 velopment by a proper supply of available mineral nutrients. 



The exact relation of organic matter in the soil to the activities of 

 nitrifying bacteria is but beginning to be properly understood. Earlier 

 observations made it manifest that heavy applications of animal manures, 

 or of green manure may not only retard nitrification, but may actually 

 cause the disappearance of a part or of all of the nitrate in the soil. Sub- 



