DECOMPOSITION OF ORGANIC MATTER IN THE SOIL 33 1 



oxidation of ammonium salts in the Rothamsted experiments in Eng- 

 land; 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 neutralize 

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

 favorable for the rapid growth of ammonif3dng, as well as of nitrifying 

 bacteria. Furthermore, the reserve of basic material serves to neutral- 

 ize the acid formed by the bacteria and prevents thus the accumulation 

 of an undue amount of acidity. 



The r61e of certain mineral «alts 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 phos- 

 phates. Generally speaking, therefore, nitrifying bacteria are stimu- 

 lated in their development 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. Subsequent experiments by Winogradski and by Winogradski 

 and Omelianski showed that in pure cultures the presence of even slight 

 amounts of soluble organic matter may depress or even suppress the 

 development of the nitrifying bacteria. It was, therefore, concluded 

 by these authors that relatively small amounts of soluble organic 

 matter may inhibit nitrification. These conclusions, based on the 



