X.] DOMINANT MANURES 281 



the Swede crop will consist in the main of phosphatic 

 material, with but a small quantity of nitrogen and 

 rarely or never any potash. For example, 4 cwts. of 

 superphosphate or 5 cwts. of basic slag, according to 

 the soil {i.e., 50 to 100 lb. of phosphoric acid), together 

 with 12 to 15 lb. of nitrogen as contained in half a 

 hundredweight of sulphate of ammonia, will form a 

 very satisfactory mixture. Swedes are sown late in 

 the season after a very thorough preparation of the soil, 

 so that the nitrification alone of the nitrogenous residues 

 in the soil is capable of furnishing almost all the large 

 amount of nitrogen they require ; they are very shallow- 

 rooted, and must be supplied with an abundance of 

 phosphoric acid. It was considerations of this kind 

 which led Ville to suggest that for each crop there is a 

 " dominant " fertilising constituent, e.g., nitrogen for 

 wheat, phosphoric acid for Swedes, and that the parti- 

 cular dominant is the constituent which the plant finds 

 the most difficulty in appropriating from the soil, and 

 which is, therefore, more often indicated by a compara- 

 tive deficiency than by an abundance in the ash of the 

 plant. Such a theory is, however, not borne out by more 

 general experiments ; many plants do not exhibit such 

 idiosyncrasies as are shown by wheat and Swedes, but 

 require a general fertiliser, the composition of which is 

 determined more by the soil than the plant. Indeed, no 

 theory of manuring can be based upon the plant alone 

 but must also take the soil into account, so that a 

 fertiliser may be regarded as rectifying the deficiencies 

 of the soil as far as regards the requirements of the crop 

 in question. What those special requirements are can 

 only be decided by experiment, just as the soil con- 

 ditions are ascertainable by trial rather than from a 

 priori considerations of analysis. If an analysis be 

 made of any soil in cultivation it will be found to 



