304 AMMONIA AND NITRIC ACID. 



duction. When the price of guano exceeds a certain 

 limit, so that the crop realised does not bear a proper 

 proportion to the outlay of capital and labour, this very 

 circumstance prevents its. application. 



From this point of view farmers might long ago 

 have perceived that the question about the necessity of 

 supplying ammonia to increase the crops of corn, in- 

 cludes another question, whether, on the whole, prog- 

 ress in this respect is, or is not, possible in agricultural 

 practice. 



A few considerations only are necessary to bring 

 the farmer to the conviction, which I myself entertain, 

 that if increased production depends upon an augmen- 

 tation of nitrogenous food in the soil, we must at once 

 renounce all idea of improvement. For my own part, 

 I am much more inclined to believe, that progress is 

 only possible and attainable if the farmer restricts him- 

 self to that store of nitrogen which he can collect upon 

 his own ground, avoiding as much as possible all pur- 

 chase of nitrogenous food from other quarters. 



On the average, all the experiments of Lawes in 

 England have shown, that/b/* one pound of salts of am- 

 monia in manures, two pounds of ivheat may ~be reaped. 



These results, we -must remember, were obtained 

 from a field in which one acre without manure of any 

 kind was able to yield, for seven years consecutively, 

 1125 Ibs. of corn and 1Y56 Ibs. of straw ; and that all 

 the plots manured with salts of ammonia also received 

 phosphate and silicate of potash.* 



On an average, Lawes manured his fields with 3 

 cwt. of salts of ammonia, and thereby he obtained half 

 as much corn again as the unmanured plot yielded. 



We will now assume that the extra crop obtained 

 was exclusively due to the salts of ammonia ; we will 



* On this point Lawes says (' Journal of the Royal Agr. Soc. of Eng.,' 

 v. xiv. p. 282), that for the production of one bushel of wheat (=64 to 65 

 pounds, containing 1 pound of nitrogen) which the soil was made to yield 

 above its natural power, 5 pounds of ammonia were requisite ( = 16 pounds 

 of sal ammoniac, or 20 pounds of sulphate of ammonia). He adds, how- 

 ever, that in no single experiment -did the extra crop obtained correspond 

 to this estimate. 



