98 



THE AGRICULTURAL NEWS. 



April 2, 1910. 



be converted, first into nitrites and then into nitrate.=, 

 by the nitrous and nitric nitrifying organisms, respect- 

 ively. It has now been ascertained definitely that this is 

 not invariably the case, for part of the sulphate of ammo- 

 nia can be absorbed directly. Thus it is not correct to 

 say absolutely that this manure is less available than 

 nitrate of soda. It acts more slowly because that part 

 which is used by plants is not all absorbed directly, but 

 some of it is converted into nitrates before it is taken 

 in by them. 



A great deal of work has been done in connexion 

 with the matter in the past, and several particular 

 conclusions have been obtained. It has been shown 

 that ammonium salts are absorbed as readily as 

 nitrates, by beans and maize. Other experiments 

 have demonstrated that ammonium salts can be utilized 

 directly by certain grasses, and that some plants can 

 thrive in the absence of nitrates. In the last case, 

 however, it was not conclusively shown that the only 

 source of nitrogen was salts of ammonia. 



The most recent investigations in connexion with 

 the subject have been conducted by Hutchinson and 

 Miller, of the Rothamsted Experiment Station, an 

 account of whose work appears in the Journal of 

 Agricultural Science, Vol. 3, Part 2. These experi- 

 menters raised sterile seedlings from sterile seeds and 

 grew them in various sterilized sand and water 

 cultures. The need for the conduct of the experiment 

 under sterile conditions is easily understood when the 

 importance is realized of eliminating those organisms 

 which can assist in the oxidation of ammonium salts to 

 nitrates. The trials were made with wheat grown in 

 sand, wheat grown in water cultures, and peas grown 

 in water cultures. The cultures, of course, contained 

 those substances that are necessary to the growth of 

 plants and, in each set of experiments, differed chiefiy 

 from one another in the presence or absence of chalk, 

 nitrifying organisms, ammonium sulphate or nitrates. 

 The results of the experiments showed (1) that 

 ammonium sulphate is absorbed directly by wheat and 

 peas, (2) that, under the conditions of the experi- 

 ment, peas thrive equally well whether they are 

 supplied with ammonium salts or nitrates, (3) that 

 wheat grows best when supplied with nitrates. 



A general summary of this work will make its 

 importance all the more evident. It shows that plants 

 of various kinds can grow in a normal manner when 

 ammonium salts are supplied to them under conditions 

 which preclude the possibility of the formation of 

 nitrates. Further, some plants grow equally well when 

 they are supplied either with ammonium salts or 



nitrates, as a source of nitrogen, but a number of these 

 appear to have a preference for nitrates. 



The investigations do not make it certain that 

 ammonium salts are ever capable of producing better 

 results than those which are obtained from the 

 use of nitrates. Nevertheless, there are indications 

 that the replacement of nitrates by them may 

 result in better yields. There are facts to show 

 that some plants prefer ammonium salts to nitrates for 

 early growth, but that nitrates are more suitable for 

 their later development. 



Attention has already been drawn to the power 

 possessed by plants to build up more complex sub- 

 stances from simpler ones. In the case of nitrogenous 

 bodies, an early step in the process is the formation of 

 compounds called amides, such as asparagin. From 

 the amides, either directly or indirectly, the complex 

 food-substances called proteids are made, and, from the 

 proteids, protoplasm is derived. In the present con- 

 nexion, the formation of amides is the important 

 consideration. These are more readily produced from 

 ammonium salts than from nitrates. It often happens 

 that plants well supplied with nitrates cease to absorb 

 them to any great extent after a time, becau.se of the 

 degree to which they have accumulated in the tissues. 

 This is not the case with ammonium salts, for these 

 will be quickly converted into amides, and thence into 

 proteids, after they have been absorbed. It is therefore 

 to be expected that plants fed on ammonium salts will 

 contain a distinctly higher percentage of nitrogen than 

 those supplied with nitrates, and the work of Hutchinson 

 and Miller shows this to be actually the case. The fact 

 is also of interest that, as has been stated above, many 

 plants prefer ammonium salts to nitrates when they are 

 young. It would seem that the reason for this, again, 

 is the circumstance that amides, and therefore proteids, 

 are formed more easily from ammonium salts than from 

 nitrates, so that, with the former bodies, the nutrition 

 of the young plant is carried on in a more speedy and 

 efficient manner. 



A similar explanation would seem to be capable 

 of application to the question as to why leguminous 

 plants usually contain a higher percentage of nitrogen 

 than plants of other kinds. The nitrogen that is hand- 

 ed on to them from the air by the bacteria in their 

 root nodules is probably in a state of combination such 

 that amides and proteids are easily formed. In any 

 case, the conclusion of value is that the efficiency of 

 the assimilation of nitrogen by plants in general may 

 be increased by employing ammonium salts as well as 

 nitrates, when it is desired to add to their nitrogenous 

 food. 



