15 



power of dung by the additioa of such substances as phosphoric acid and 

 potash, but it would appear to be reasonable to suppose that it is due to 

 the better nourishment of the denitrifying bacteria under the influence 

 of abundance of available phosphatic and potassic food. They have 

 shown chut the organisms can be largely destroyed (a) by frequently 

 turning dung-heaps, so as to induce rapid fermentation, oxidation, and a 

 high temperature, and (b) by adding certain substances, of which the 

 most effective were found to be sulphuric acid and copper sulphate. 

 And similarly, as has been indicated, there are doubtless substances that 

 favour the growth and development of the organisms, and it would ap- 

 pear that some of our commoner artificial manures must be placed 

 amongst the number. The whole subject is of such far reaching impor- 

 tance to agriculturists that it is to be hoped it will in the near future re- 

 cieve in this country, the scientific attention that it appears to deserve 



William Somerville, 

 Durham College of Science, Newcastle-ou-Tyne. 



DENITRIFICATION AND FARMYARD MANURE. 1 



In the preceeding article Dr. Somerville has given a clear account 

 of the very remarkable conclusions arrived at by modern German inves- 

 tigators respecting the behaviour of farm yard manure when applied 

 tinder various circumstances to the soil. These conclusions, if established, 

 would seriously modify our ideas as to the value of this manure, and as 

 to tl e conditions under which it can be most profitably employed. The 

 German experiments have been not only numerous, but have been con- 

 ducted with great care and skill. We have, however, always to distin- 

 guish between the facts proved by experiment, and the conclusions 

 drawn from them. The results of the experiments are undoubtedly true, 

 and demand most careful consideration ; but to interpret these results, 

 to grasp the principles which underlie the actions observed, we must 

 first of all be thoroughly acquainted with all the circumstances of the ex- 

 periments, and we must at the same time take into account any other 

 facts bearing on the question at issue. A true theory is one which will 

 explain all the facts, and not merely some of them. 



The conclusions arrived at by Wagner and Maercker, with which we 

 have in the first place to deal, are briefly the following : — 



1. The solid excrement of the horse and cow is practically without 

 value as a manure for plants. 



2. When applied to the land, fresh horse or cow dung (2) destroys 

 the nitrates naturally contained in the soil, or added to it in the form 

 of nitrate of sodium, and the crop which immediately follows is con- 

 sequently less than if no dung had been applied. 



(1) From Journal of Royal Agricultural Society of England, Vol. VIII 



(2) In this paper the term u dung" is used to designate the solid excre- 

 ments unmixed with urine or litter ; while " formyard manure" is employed in 

 its usual sense, as the name for the mixture of the solid and liquid voidings of 

 the animal with litter. 



