CHAPTER IY. 



FAKM-YAKD MANURE. 



The fertility of a soil depends upon the sum of available food, the continuance of 

 the fertility upon the total amount of all food in it Chemical and agricultural 

 exhaustion of the soil Exhaustion of the soil by cultivation, laws regulating 

 its progression effect of the transformation in the soil of the chemically fixed 

 into physically fixed elements of food ; effect on the progress of exhaustion by 

 partial restoration of the withdrawn food of plants Progress of the exhaustion 

 by different cultivated plants Cultivation of cereals, consequence of removing 

 the grain and leaving the straw in the soil ; intervening clover and potato 

 crops ; effect of leaving in the ground the whole or a portion of these crops ; 

 division of soils ; productive power of wheat fields increased by accumulating 

 in them the materials derived from clover and potato fields ; cultivation of 

 fodder plants ; their food partly derived from the subsoil ; addition of these in- 

 creases the productive power of the surface soil Natural connection between 

 the cultivation of cereals and fodder plants, the influence on the fertility of 

 land Exhaustion of the soil removed by the restoration of the withdrawn 

 mineral constituents ; the excrement of men and animals contains these ; their 

 restoration depends upon the agriculturist. 



TO form a correct idea of the effects produced by 

 farm-yard manure in husbandry, it must be remem- 

 bered that the fertility of a soil is always exactly pro- 

 portionate to the amount which it contains of nutritive 

 substances in a state of physical combination ; and that 

 the permanence of its fertility or its productive power 

 stands in proportion to the total quantity of the con- 

 stituents in the soil capable of passing over into that 

 physical condition. 



The amount of crop reaped from a field in a given 

 time is proportionate to that fraction of the total con- 

 stituents which has passed during this time from the 

 ground into the plants grown upon it. If one of two 

 fields yields twice as large a crop of wheat and straw as 

 the other, this necessarily presupposes that the wheat- 

 plants upon the one field have received from the ground 

 twice as much nutriment as those upon the other. 



