31G MIMONIA AND NITRIC ACID. 



weight of farm-yard manure, if we ascribe the effect of 

 the latter merely to the amount of ammonia which it 

 contains, then the unfruitfulness of the field at Schleissheim 

 is entirely inexphcable. 



We assume that the entire quantity of nitrogen in 

 farm-yard manure has a definite share in its operation ; 

 and as the nitrogenous matters in the arable soil are ori- 

 ginally identical with the substances which form the 

 constituents of manures, it is impossible to ascribe to the 

 one an effect which does not equall}^ ^pplj to the other. 



There can be no doubt that the nitrogenous compounds 

 m the ground often exert no influence in increasing the 

 crops, Avliile those in the manures undoubtedly produce 

 a favourable effect. Hence the operation of the nitro- 

 genous compounds in the manure must have depended 

 upon causes which the ground did not supply; and it is 

 clear that the same efficacy can be given to the nitro- 

 genous compounds in the soil, if the farmer will take 

 care to bring into play the causes which produced the 

 favourable operation in the maniu"es. 



If we consider, for example, the crops yielded (see 

 pp. 147 and 150) by the two fields at Schleissheim in an 

 unmanured condition, and compare them with the quan- 

 tity of nitrogen in the soil, the result is — 



jSfitrogen, per hectare (= 2-^- acres). 

 To the depth of 10 inches. 



In Field 1 (p. 150), 1858 

 In Field 2 (p. 147), 1857 



Those who maintain that the crops depend upon the 

 nitrogen in the soil, would judge the results of these two 

 experiments somewhat in the following way : — 



The amount of nitrogen in both fields is as . , . 100:160 

 The corn crops as 100 : 560 



