On Agricultural Chemidrij. 



241 



season, and the description of the growing plant. It is known, 

 however, that although the climate of any place may vary one 

 year as compared with another, it nevertheless maintains a certain 

 average. It may be supposed therefore that the natural produce 

 of the soil, in any particular locality, would be uniform in a series 

 of years. 



The effect of rain is to dissolve a certain partion of the mineral 

 matter of the soil : it also supplies carbonaceous matter and am- 

 monia. Liebig found ammonia in the rain at Giessen. The rain 

 collected in a vessel placed on the top of a tree in my wheat-field, 

 at a distance from any building, gave, upon evaporation, a liquid 

 having a foetid smell, and yielding ammonia to suitable re-agents. 

 The rain collected in a rain-gauge placed in a garden at Mam- 

 head, in Devonshire, had the taste of soot, although the wind was 

 blowing direct from the sea during its fall. Rain is therefore 

 capable, to a certain ex:tent, of supplying plants with ammonia. 

 Carbonic acid is also a constant and important constituent in rain- 

 water, as well as in the atmosphere itself. The atmosphere may 

 thus be considered the natural source of organic, and the soil that 

 of inorganic, supply. It is the object of agriculture to increase 

 the produce of the soil beyond its natural yield, which can be done 

 by various means. The field may be fallowed — that is to say, 

 the natural produce of the soil for two years may be concentrated 

 into one — ^the repeated exposure of the soil to the atmosphere, by 

 means of ploughing, causing a decomposition of mineral matter, 

 while the ammonia in the rain unites with the various acids in the 

 soil. The produce of the soil may also be increased by means of 

 manures — that is to say, by supplying those ingredients which the 

 soil and the atmosphere are incapable of yielding in sufficient 

 quantity for an agricultural result. This process I shall now en- 

 deavour to explain. It will be remembered that the produce of 

 wheat and straw upon the unmanured portion of my experimental 

 field was greatest in the year when the atmosj)heric influence, 

 and therefore the supply of ammonia, was the most ; but in no 

 case was a full agricultural crop obtained. This may be attri- 

 buted to two causes : either that the wheat was incapable of assi- 

 milating what the atmosphere and rain could supply, for want of 

 an available amount of minerals in the soil ; or that the minerals 

 in the soil were in excess, but that the wheat was incapable of 

 assimilating them for want of a sufficient supply of ammonia, or 

 other organic substances. 



It has been argued by Liebig that the atmosphere can supply 

 the ammonia from which plants derive their nitrogen, in sufficient 

 quantity for agricultural purposes ; and his views on this subject 

 have been echoed through England by a host of his followers. 

 This point, upon which so much difference of opinion exists be- 



VOL. viir. R 



