406 REID AGRICULTURE ALLIED TO CHEMISTRY. 



of all well tilled soils. The other gaseous or aerial constituents ^ 

 and a large portion of the nitrogen are not so renewed, and hence 

 need the most frequent repletion and must be furnished in the 

 largest percentage by the most profitable manures. In fact we 

 have returned to the previous theory of Boussingault. 



The ash of plants contains potassa, soda, lime, magnesia, iron, 

 phosphoric and sulphuric acids, silica, &c,, &c. , derived from the 

 soil. Liebig taught *' supply these in a soluble form in sufficient 

 quantity and the plant demands nothing more in the way of food ; 

 with these it is able to assimilate carbonic acid, water and ammonia 

 from the air, without them it cannot." Liebig's '* Mineral Man- 

 ures" were the natural outcrops of such teaching, — much was 

 expected from them, but comparative failure resulted. 



Farmers voted sientific agriculture a delusion and returned to 

 the good old way that had been handed down from father to son for 

 ages, and yet they could see that their lands were getting run out 

 thouofh knowino' not how to correct their condition. 



JSfo country demands more from its soil than Great Britain, and 

 no people are better qualified to reduce theories to a financial basis ; 

 hence it is natural that we should look to England for correct 

 practical as well as scientific agriculture. To get the grains of 

 truth out of the mass of chaff abounding in all theories, and as well 

 to still farther enlarge the domain of our knowledge, an experi- 

 mental farm at Rothamsted, England, was carried on for over 20 

 years (from 1843 to 1864, when reports were given) by Lawes 

 and Gilbert. They gave to the world the most practical and 

 scientific agriculture that had yet obtained, and whose results stand 

 the test of continued experience. Every conceivable theory and 

 experiment was tried and the results given in plain and explicit 

 figures and opinions. To these as I am able to understand them, 

 and as briefly as possibly, I would wish to direct your attention. 



Continued crops of the same kind without manure and from 

 the same soil, exhaust the soluble ash constituents demanded by 

 that plant and as well the organic elements it requires for food, and 

 that are present in more or less quantity in all soils. 



Rotation of crops is good husbandry, because different plants 

 require different mineral food, and a soil deficient for one plant 



