388 



SCIENCE. 



[N. S. Vol. XXIV. No. 613. 



should be able to give positive advice. 

 Hence, this is a problem for the chemist, 

 and one worthy of his best thought— he 

 must find out what the cause of apparent 

 exhaustion is, and he should be able to 

 show the farmer what his sources of loss 

 are and be able to suggest a remedy. It 

 has been shown by many experiments that 

 in the ordinary and common methods of 

 farm practise, there is a loss of the im- 

 portant element nitrogen, from the soil, 

 greater than that accounted for by the re- 

 moval of crops, and, furthermore, that the 

 judicious application of commercial fertil- 

 izer or of yard manures does not result in 

 proportionately increasing, or even main- 

 taining the content of nitrogen in such 

 soils. The chemist, with his present 

 knowledge, advises that the loss may be 

 due to either of three causes, or of one or 

 more combined, viz., percolation into the 

 drains, oxidation, or denitrifieation, but 

 they are unable to suggest a method of 

 practise which will remove the cause of 

 loss. This is a problem of the first im- 

 portance, the solution of which must rest 

 with the chemist. 



It is true that one phase of the nitrogen 

 problem has been solved, but it has refer- 

 ence to the possible gain of nitrogen to 

 soils, and thus in a sense compensates for 

 the losses, though it makes the question of 

 losses none the less important. I have 

 reference, now, to discoveries that have 

 been made, in regard to the symbiotic ac- 

 tion of certain bacteria, which give to the 

 leguminous plants their power of absorb- 

 ing nitrogen from the air, and dispose of 

 the question, in the sense that so long as 

 the farmer judiciously uses any one of this 

 class of crops in his rotation, it will be 

 possible for him to, not only maintain, 

 but to even increase the nitrogen content 

 of his soils, and thus make the question of 

 exhaustion from that standpoint one not to 



be feared. It seems to me, however, that 

 we have but reached the threshold in these 

 investigations, for while as a matter of 

 fact such a practise will result in adding 

 this important element to the soil, it does 

 not dispose of the question of the full util- 

 ization of the nitrogen acquired. We have 

 many instances of attempts made to im- 

 prove soils, or to maintain their fertility 

 by the introduction of leguminous crops, 

 which have proved disastrous, rather than 

 helpful, in promoting plant growth, or of 

 permanently increasing fertility in this re- 

 spect. Furthermore, we have no definite 

 knowledge as yet, as to the conditions 

 which are necessary in order that the 

 plants shall appropriate nitrogen from the 

 air, rather than from the soil, nor have we 

 any definite information as to how large a 

 proportion of the nitrogen so gathered is 

 retained in the soil for the use of cereal 

 and other crops which depend entirely 

 upon soil sources for their nitrogen. I 

 feel certain that no agricultural chemist 

 of the present day would dare to risk his 

 reputation on a positive statement, in refer- 

 ence to any one of these phases of the ques- 

 tion. The nitrogen question in agricul- 

 ture is far-reaching in its influence, affect- 

 ing not only those who cultivate the soil, 

 but those who depend upon its products 

 for their sustenance and profit ; it is a ques- 

 tion which has occupied the student of 

 chemistry from the earliest times, and the 

 various theories advanced have caused no 

 end of controversy among them, yet in 

 many of its phases it is still a problem to 

 be solved. 



Another question, closely associated 

 with this one of nitrogen, if not intimately 

 connected therewith, is that of the impor- 

 tance of humus in relation to fertility. It 

 has been recently stated by an eminent 

 experiment station director that 'the min- 

 eral elements form but the skeleton of the 



