KIUIOR IN USING TOO MUCH MANUKIi. 215 



dust, rnpe-cake, and otlier substances containing only cer- 

 tain constituents of farm-yard manure ; and their opera- 

 tion is explained, in effect, by the doctrine of minimum, 

 which I have just laid down. 



But as the practical former is not acquainted with 

 the law which regulates the operation of these manuring 

 agents as affecting the increase of produce, he can, of 

 course, have no correct notion of their rational, which 

 means theii* truly economical, use ; he puts on his land too 

 much, or too little, or chooses the wrong agent. The 

 error of employing too little manure needs no expla- 

 nation ; for every one knows that the right proportion of 

 manure will, with exactly the same labour and at a 

 trifling additional outlay, ensure the maximmn produce of 

 which the land is capable. 



The error of using too much manure arises from the 

 mistaken notion that the action of manures is propor- 

 tionate to the quantities in which they are applied ; this 

 is true up to a certain limit, but beyond this all the 

 manure applied is simply thrown away, as far as any fer- 

 tihsing action is concerned. 



A manuring experiment made by Mr. J. Eussell, of 

 Craigie House ('Journal of the Eoyal Agr. Soc. of Eng- 

 land,' vol. xxii. p. 86), may, perhaps, serve to illustrate 

 our meaning. In this experiment a field was divided 

 into a number of plots of three rows each, all planted 

 with turnips, some of the plots being left uinnanured, the 

 remainder dressed severally with different manuring 

 agents, among others Avith superphosphate (bone-ash 

 dissolved in sulphuric acid). The produce, calculated 

 per acre, was as f(jl]o\\'s : — 



