ARABLE SOILS ABSORB FUNERAL MATTERS. 133 



W\\en two fields are equally rich in nutritive substances, 

 it often happens that the one, by tillage alone, or by tillage 

 combined with manuring, will be brought much sooner 

 than the other into a condition to yield a succession of 

 remunerative crops of cereal or other plants. 



On a hght sandy soil, all kinds of manure act more 

 rapidly and effectively than on clay. The sand is more 

 grateful, say the farmers, for the manure bestowed upon 

 it, and yields a more abundant return than other soil^ for 

 Avhat 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 favourable influence upon 

 many plants than ammonia itself. In other cases, bone- 

 earth acts more powerfully upon the future crop than 

 superphosphate of hme ; 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 phosphoric acid, 

 ammonia, potash, and silicic acid from their solutions. 

 The restoration of the productive power to an exhausted 

 field by the mechanical operations 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 dispersed 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 superaljundant deposits he to each other, the sliorter 

 is the way over which the substances have to travel ; and 

 the less the absoqitive power of the intervening earth 



