﻿6 BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 



from nitrogen starvation when growing in acid humus. For such 

 crops the neutralization of the acidity by lime is of vital impor- 

 tance, for not until this is done can the nitrogen of the humus, how- 

 ever abundant, be changed into nitrates. Whatever other direct 

 injurious effect acidity may have on crops, the fact that it checks 

 the nitrification of humus is of itself sufficiently important and sig- 

 nificant to justif}^ all the investigation that the subject has received. 



SOURCE OF NITROGEN FOR ACID-LAND PLANTS. 



•There is another phase of the acidity question. Many plants thrive 

 in soils which are acid and which therefore theoretically can produce 

 no nitrates. There are three possible methods by which these plants 

 may secure their nitrogen : 



(1) Although a sample of soil when tested as a whole shows an 

 acid reaction, there may exist in it innumerable minute tracts, sur- 

 rounding particles of lime, where the reaction is alkaline and where 

 nitrates are in process of manufacture. It is to be hoped that inves- 

 tigators will find some means to determine the possibility of such 

 a method of nitrogen nutrition in acid soils. 



(2) Many acid soils contain a large amount of nitrogen in the 

 form of ammonia, and while hitherto scientific opinion has been much 

 divided over the question whether ordinary crop plants can utilize 

 ammonia nitrogen directly, without transformation hj bacteria into 

 nitrates, careful chemical investigation under such conditions as 

 to eliminate the possibility of bacterial action should enable us to 

 determine which of our crop plants can feed on ammonia nitrogen 

 and which can not. Intelligent agriculture needs this information. 



(3) It is conceivable that a crop plant might utilize nitrogen that 

 existed in organic form in the humus of the soil, having not yet 

 reached the ammonia stage of decomposition. It is agreed by plant 

 physiologists that ordinary plants, those bearing green foliage, are 

 unable to do this. It is also agreed by plant physiologists that fungi 

 not only can but habitually do use organic nitrogen. These two facts 

 warrant the consideration of a remarkable partnership that exists 

 between certain leaf-bearing plants and certain fungi, a partnership 

 the significance of which has only recently begun to be appreciated by 

 botanists and is almost unknown in agricultural literature. 



The subject is well illustrated in the blueberr}'. The possibility of 

 the culture of this wild berry has been under investigation for several 

 years, the experiments having now reached a successful conclusion. 1 



1 Experiments in Blueberry Culture, United States Department of Agriculture, Rureau 

 of Plant Industry, Bulletin 193, 1010; also Directions for Blueberry Culture, United 

 Slates Department of Agriculture, Bureau of riant Industry, Circular 122, pages 3 to 11, 



101::. 



