12 



that ammoniacal nitrogen cannot be directly used by plants. 

 That this, however, is not the case has been shown by many 

 investigators. A. Muntz grew various plants in a soil the 

 only nitrogen of which was in the form of sulphate of 

 ammonia ; and though taking full precautions against nitri- 

 fication, he found that the plants took up large quantities 

 of the nitrogen." About thirty years ago Hampe had 

 come to the same conclusion,! but found that, in the early 

 stages of growth, plants seemed less able to use ammoniacal 

 nitrogen ; and Wagner and others have obtained similar 

 results. We may assume, however, that ammonia is not 

 taken up so readily as nitric nitrogen i.e., nitrogen in the 

 form of nitrates ; and under practical conditions the ammonia 

 of manures is almost always converted into the nitric form 

 before being used by plants. 



Though nitric nitrogen is stored up in the plant for a time, 

 until circumstances allow of its being utilized, ammonia 

 compounds are not to any appreciable extent, but are con- 

 verted at once into a substance called asparagine. This 

 can only be formed when carbohydrates are present. If 

 they are deficient, compounds of ammonia act as plant 

 poison sulphate of ammonia perhaps least so. J 



In connection with this action, and the importance of the 

 presence of carbohydrates in the plant when ammoniacal 

 manures are used, it is worth repeating that mineral manures, 

 and potash particularly, are necessary to enable the plant 

 to form carbohydrates. The results of many experiments 

 seem to show, as we shall see, that by withholding a full 

 supply of potash from the soil, the action of ammonia com- 

 pounds is more injuriously affected than that of other forms 

 of nitrogenous manures. 



The asparagine and other amides formed are not the final 

 product from the nitrogen which the plant takes up. In the 

 mature plant particularly, albuminoids are found in consider- 

 able quantities, these being formed from the amides. Among 

 other requirements for their formation, besides those already 

 mentioned, it is worth noticing that the presence of a sulphate 

 is essential. As Liebig pointed out, sulphate of ammonia 

 may gain in effect from this cause ; but the cases in which 

 it does so must be few, for sulphates are practically always 

 present in the soil in sufficient quantity for the plant's require- 

 ments. 



ABSORPTION OF AMMONIA BY SOILS. 



We may now pass on to consider what happens w r hen sul- 

 phate of ammonia is applied to the soil. The actions and 

 changes to be described take place in the same way with 

 other compounds of ammonia, but the sulphate is the form 



* " Comptes Kendus," 109. f Vs. St., 10. + Bui. Coll. Ag. Imp. Univ. 

 Tokyo, 1895. " Chemistry of Agriculture and Physiology." Third Ed. 



