On Agricultural Cliernidry. 



247 



than that of the amount of ammonia required to produce a bushel 

 of corn, they will enable any one to judge of the probable exact- 

 ness of the estimate which has just been made. It should be 

 remembered, however, that as the season of 1846 was more than 

 usually favourable to the production of corn, any calculations 

 founded upon the results of that year might lead to an over- 

 estimate of what the ammonia would produce in an average of 

 years. The produce of the unmanured space and that of farm- 

 yard dung was — 



Bush, plis, gals. Straw in lbs. 



No manure . . 17 3 3 1513 

 14 tons of dung . . 27 0 3 2454 



It was my intention to conclude this paper with some experi- 

 mental evidence relative to the influence of climate and manures 

 upon the turnip and leguminous crops ; but, having extended my 

 observations upon the corn-plants to a greater length than I had 

 at first contemplated, I shall defer the consideration of that 

 subject to a future period. I wish, however, to make a few ob- 

 servations upon the general principles of practical agriculture. 

 Some of them are apparent from the evidence I have already 

 brought forward, but some of them are indicated by the results 

 of other branches of the investigation than those which I have dis- 

 cussed in the foregoing pages. 



I have said that soil and atmosphere are the two great natural 

 sources from which plants derive the elements of their growth ; 

 the former supplying the inorganic and the latter the organic 

 elements. Besides the minerals of which soils are principally 

 composed, they contain a certain amount of organic matter ca- 

 pable of yielding carbon and ammonia to plants ; and the annual 

 amount of ammonia which a soil is competent to yield under the 

 influence of the atmosphere must to a certain extent determine its 

 natural fertility. A Russian soil, said to be one of the inost fertile 

 in the world, and which yields fine wheat without manure, gave 

 when analysed by M. Peyen, 24J^ lbs. of nitrogen in 1000 lbs. of 

 soil, or nearly 2 J per cent. A very fertile soil sent to me by Sir 

 John Tylden from Somersetshire, and said to yield 40 bushels 

 of wheat annually without manure (a statement afterwards proved 

 to be incorrect), was analysed by Dr. Gilbert in my laboratory, 

 and gave 6 • 2 lbs. of nitrogen in 1000, or rather more than \ per 

 cent. ; whilst from the soil of my experimental field, which yields 

 about 17 bushels of wheat annually without manure, he obtained 

 in 1000 parts only 2*0 of nitrogen, equal to l-5th per cent. Al- 

 though the amount of nitrogen in a soil, independently of any 

 immediate supply, may determine to a certain extent its powers of 

 producing corn, it is not a sure criterion of the value of different 

 descriptions of soil. The rich clayey soils, in which the largest 



