•322 Afjricnltural CJiemistrij. 



But Messrs. Lawes and Gilbert have, without being aware of 

 it, supplied the most decisive proof that the accumulation of am- 

 monia in the soil, in one year, has no influence on the crop in the 

 succeeding year. They manured a field in 1845 with 336 lbs. of 

 ammoniaral salt, of which no more than 72 lbs. could be employed 

 in the increase of produce obtained. The residue, 254 lbs., which 

 remained in the soil, had no influence on the crop of 1846. After 

 a new manuring with ammoniacal salt, there was a new residue 

 of 206 lbs. ; but even the two together (=634 lbs.) was equally 

 without eflfect in 1847. At last the residue of ammoniacal salt in 

 the soil amounted to 1192 lbs. ; but even this had lost all influence. 

 In all these trials with ammoniacal salts, even when an enormous 

 excess was used, the accumulation of ammonia in the soil was 

 found to have no effect in the following season. 



But if in this way clear proof is obtained that the accumulation 

 of am.monia in the soil does not increase its fertility in the follow- 

 ing year ; if, moreover, the ammonia be added to the soil in the 

 form of a non-volatile salt, how can it rationally be supposed that 

 the quantity of ammonia which is possibly conveyed to the soil by 

 the air and rain, which is from three to five times smaller, can 

 have a perceptible influence on the fertility of the soil ? when 

 we know, in addition to all this, that the soil contains many hun- 

 dred times, nay often a thousand times, as much ammonia as is 

 required for a full crop of wheat. From this want of effect, these 

 writers draw the conclusion, tliat the ammonia has evaporaied and has 

 been dissipated through the leaves and stalks ! But this conclusion 

 is not a fact ; it is a pure fancy ; and has been imagined in order 

 to save their so-called theory. In a similar way do they proceed 

 in a series of experiments on the cultivation of turnips. They 

 manured a field for several years with superphosphate of lime. 

 In 1843 it received 504 lbs."; in 1844, 560 lbs. ; and in 1845, 

 1232 lbs. ; in all, 2296 lbs. of superphosphate of lime. In the 

 three crops of turnips there were removed from the soil, in each, 

 about 112 lbs. of superphosphate, in the three years therefore 

 336 lbs., and there remained in the soil 1960 lbs. of superphos- 

 phate for the crop of the fourth vear. But now v.as presented 

 the strange circumstance, that this field, though it contained after 

 the third crop, nearly four times as much superphosphate as was 

 supplied in the first year, yet required to be manured, in the fourth 

 year, with 280 lbs. of superphosphate, in order to yield a fourth 

 crop. While 504 lbs. in the first vear had a most marked effect, 

 1960 lbs., present, after the third crop, had no effect on the crop of 

 the fourth. There is no room for supposing a want of phosphoric 

 acid ; for the soil contained, in the fourth vear, four times as 

 much as in the first, and yet lost its productive power. The 

 phosphoric acid lost its eflScacy ! This case is quite parallel to 



