No. 4.] CHEMICAL AND FARM MANURES. 157 



fact that in the process of decomposition much of the bac- 

 terial food is destroyed, and in consequence the subsequent 

 tendency to decompose nitrates is reduced. In recent green- 

 house experiments at the Rhode Island station, where stable 

 manure only partially rotted was applied at the rate of 

 seventy-five tons per acre, it ceased to support the growth 

 of plants after the removal of two crops of radishes and one 

 of lettuce, and experiments revealed the fact that it was due 

 to the absence of nitrates. Where chopped hay was mixed 

 with the soil, nitrate nitrogen practically disappeared in a 

 comparatively short time, which was not the case where 

 organic matter was not applied. It is recorded that Lawes 

 and Gilbert found a marked lack of durability in the nitro- 

 gen of stable manure when large quantities were applied to 

 the land annually for several years, which is unquestionably 

 explainable upon the same ground. 



The more perfectly herbivorous animals digest their food, 

 the less is the tendency of the manure to cause the reduction 

 of nitrates. The ground for this is that, with the more 

 thorough digestion, less food suitable for the growth of the 

 denitrifying organisms remains in the ffBces. This may ex- 

 plain why, for certain purposes, sheep manure is preferred 

 by many in greenhouse work (where much manure is incor- 

 porated into a small body of soil) to cow manure, and par- 

 ticularly to horse manure. 



Magnesia. 



Magnesia, though essential to plant growth, is not usually 

 looked upon as sufficiently lacking in soils to render its ap- 

 plication to them necessary. In all probability, sulfate and 

 perhaps other salts of magnesia may act like gypsum (land 

 plaster) in setting free potash and other manurial substances 

 for the use of plants. It is possible, also, that magnesia 

 may be lacking in certain soils to a greater extent than is 

 usually supposed. Larbaletrier and Malpeaux * report sev- 

 eral trials in which marked benefit from its use in France 

 was observed ; and recent unpublished experiments, con- 

 ducted at the Rhode Island station in natural soil liberally 

 supplied with the customary manurial substances have given 



* Annales Agronomique 22 (1896), pp. 20-32. 



