94 



NfTROCEAOUS MANURES 



[chap, 



the nitrification of the ammonia continues the supply 

 of nitrate at a later stage, and the injurious effects 

 upon the soil of the two manures, nitrate of soda as 

 a producer of alkali, and sulphate of ammonia as causing 

 acidity, neutralise one another. 



Several of the organic compounds of nitrogen, such 

 as those contained in Peruvian guano, rape cake, and 

 dried blood, arc almost as active sources of nitrogen as 

 the salts of ammonia, especially when used continuously, 

 so that the residues left in any one year are available 

 for succeeding crops. For example, the Rothamsted 

 barley plots receive equal weights of nitrogen as 

 nitrate of soda, sulphate of ammonia, and rape cake ; 

 and as the following table shows, the returns from the 

 rape cake are but little below those from the other two 

 manures. 



Taui.k .\ XV I. —Nitrogenous Manures with Minerals. 

 Average Yield of Barley (i852-I9oi> Rothamsted. 



These results do not, however, show how much 

 return from the given manure is obtained in the year 

 of application, but from other of the Rothamsted plots 

 we learn that on such a soil neither nitrate of soda nor 

 ammonium salts leave any appreciable residue behind. 

 On the wheat field, two of the plots receive in alternate 

 years cither 400 lb. of ammonium salts or a mixture of 

 complete mineral manures ; so that in any year there is 

 one plot with the ammonium salts and the residue of 

 the previous year's minerals, and another with mineral 



