136 ACTION OF SOIL ON FOOD OF PLANTS IN MANURE. 



soils for what it has received. The nitrogenous 

 manures, such as wool, horn-shavings, "bristles, and 

 blood, which, as we know for a certainty, act by the 

 formation of ammonia, frequently exercise a far more 

 favorable influence upon many plants than ammonia 

 itself. In other cases, bone-earth acts more powerfully 

 upon the future crop than superphosphate of lime ; and 

 sometimes ash will prove more fertilising than if the 

 amount of potash contained in it were directly laid 

 upon the field. 



All these facts are most intimately connected with 

 the faculty of arable soils to extract or absorb phos- 

 phoric acid, ammonia, potash, and silicic acid from 

 their solutions. The restoration of the productive 

 power to an exhausted field by the mechanical opera- 

 tions of tillage and fallowing alone, without manure, 

 presupposes that in certain parts of the field there must 

 have been an excess of nutritive substances which dis- 

 persed in the soil and extended to other places where 

 such substances were deficient. 



This distribution demands a certain time. The 

 excess of nutritive elements must first be dissolved, that 

 they may be able to move towards those parts which 

 have lost their elements of food by a previous harvest. 

 The closer these superabundant deposits lie to each 

 other, the shorter is the way over which the substances 

 have to travel ; and the less the absorptive power of 

 the intervening earth particles for these nutritive sub- 

 stances, the more speedily will the productive power 

 of the soil be restored. 



Every arable soil possesses, for potash and the other 

 substances mentioned, a determinate power of absorp- 

 tion, which may be expressed by the number of milli- 

 grammes absorbed by 1 cubic decimetre ( = 1000 cubic 

 centimetres) of earth. Thus, for instance : 



Cubic Cubic 

 decimet. inches. Milligrammes. Grains. 



1 = 61 of lime soil from Cuba absorbed 1360 = 21 potash. 



1 " loam " Bogenhausen " 2260 = 35 " 



1 " soil " Weihenstephan " 2601 = 40 " 



1 " soil " Hungary " 3377 = 52 " 



1 " garden mould " Munich " 2344 = 36 " 



