24 CHARACTERISTICS OF AMMONIA SALTS 



As no examination of the soils was made until 12 days had 

 elapsed, we have here no indication of the minimum time 

 required for nitrification to commence. Wagner's method 

 moreover always underrated the extent to which the ammonia 

 salt had nitrified. He apparently arrived at the amount of 

 ammonia which had nitrified by deducting from the nitric acid 

 in the manured soil the quantity found at the same date in a 

 similar unmanured soil. This method always leads to low 

 results, as experiments have shown that the organic matter of 

 a soil nitrifies very little while the nitrification of added 

 ammonia is in progress. The action of the nitrifying organisms 

 in a soil is in fact limited, and they attack by preference the 

 ready formed ammonia present. 



In the case of the autumn application of ammonia salts in 

 the Rothamsted Wheat field, it is evident from the figures 

 already quoted (Table I.) that nitrification had distinctly com- 

 menced forty hours after the dressing had been ploughed in. 

 In Schloesing's numerous laboratory experiments, in which the 

 ammonia salts were dissolved in water before they were 

 added to the soil, nitrification was completed in 8 to 15 days ; 

 and this was the case when a far larger proportion of ammonia 

 was added to the soil than would ever be used in practice. If 

 therefore the soil is in a suitable condition of tillage, and rain 

 falls abundantly immediately after the application of the sul- 

 phate of ammonia, so as to at once distribute it throughout 

 the soil, we may probably assume that nitrification will be 

 concluded in a fortnight after the application. On the other 

 hand, in the absence of rain, or from the lack of other favour- 

 able conditions already mentioned, the time required for com- 

 plete nitrification may be very considerably prolonged. 



3. Exhaustion of Lime. In describing the changes 

 which sulphate of ammonia undergoes in the soil, we have 

 seen that, in the first place, the sulphuric acid of the salt 

 combines with the carbonate of lime in the soil ; and that, 

 in the second place, the nitrous acid formed by the oxidation 

 of the ammonia also combines with carbonate of lime. Lime 

 may not be demanded for these reactions if the soil contains 

 in the place of lime other bases, as alkalies and magnesia, 



