III.] DOMINANT FERTILISERS 89 



When various crops are considered in relation to 

 manures, they are found to show considerable difft^rences 

 in their response to the individual elements of nutrition, 

 differences which arc only to be ascertained by trial, 

 but which are not determined by the greater or less 

 amount of the fertilising ingredient in question taken 

 up from the soil. For example, Ville introduced the 

 idea that for each plant there is a "dominant" element 

 of fertility, and if the requirements of the plant in this 

 respect are satisfied it is generally capable of obtaining 

 the other necessary constituents from the soil. For 

 wheat, grass, and mangolds, nitrogen is the dominant ; 

 under ordinary conditions of farming if the wheat crop 

 is well supplied with nitrogen it is waste of money 

 to give it any phosphatic manure or potash salts, 

 because neither will result in any adequate increase 

 of crop, supposing the soil to show no abnormal 

 deficiencies. Without pushing the idea too far, it may 

 generally be recognised that when the land is in good 

 condition most of our crops require a special, rather 

 than a general manuring ; the plant, owing to some 

 peculiarity in its habit of growth, finds a particular 

 difficulty to obtain one of the constituents of its nutri- 

 ment from the soil ; if that weak spot is repaired by 

 the manure employed, the soil will furnish the other 

 essentials for growth. For example, wheat and barley, 

 cereals that are so similar in their general character, 

 demand entirely distinct treatment ; under ordinary 

 farming conditions, wheat, as we have stated above, 

 requires an active nitrogenous manure and little else; 

 barley requires comparatively little nitrogen, but is very 

 responsive to a supply of phosphates. 



This contrast between wheat and barley is due to 

 the differences in the time and growth of the two 

 plants : wheat is generally grown in the autumn after 



