COMMERCIAL FERTILIZERS 495 



has been demonstrated by KeJlner * and later by Kelley. 2 

 On upland soils, however, it is presumable that rice plants 

 utilize nitrate nitrogen, wjrich would indicate that some 

 plants, at least, may adapt themselves to the use of the 

 more abundant form of nitrogen. 



Hutchinson and Miller 3 found that peas obtained 

 nitrogen from ammonium salts as readily as from sodium 

 nitrate, but that wheat plants, although able to obtain 

 nitrogen directly from ammonium salts, grew much better 

 in a solution containing nitrates. One feature brought 

 out by the numerous experiments with ammonium salts 

 is the difference between plants of various kinds in respect 

 to their ability to absorb nitrogen in this form. 



419. Utilization of humus compounds by plants. — 

 One of the early beliefs in regard to plant nutrition was 

 that organic matter as such is directly absorbed by higher 

 plants. This opinion was afterwards entirely replaced 

 by the mineral theory propounded by Liebig; and still 

 later the discovery of the nitrifying process almost dis- 

 posed completely of the belief that organic matter, is a 

 food for higher plants. It is quite certain, however, that 

 some organic nitrogenous compounds furnish suitable 

 nutrient material for some higher plants without under- 

 going bacterial change. 



Hutchinson and Miller, in the paper just referred to, 

 give the following list of the organic substances used in 



1 Kellner, 0. Agrikulturchemische Studien liber die Reis- 

 kiiltur. Landw. Vers. Stat., Band 30, Seite 18-41. 1884. 



2 Kelley, W. P. The Assimilation of Nitrogen by Rice. 

 Hawaii Agr. Exp. Sta., Bui. 24, pp. 5-20. 1911. 



3 Hutchinson, H. B., and Miller, N. IT. J. The Direct 

 Assimilation of Inorganic and Organic Forms of Nitrogen by 

 Higher Plants. Centrlb. f. Bakt., II, Band 30, Seite 513-547. 

 1911. 



