234 CAUSES OF FERTILITY AND STERILITY [chap. 



years of skilful management makes a good pasture, 

 the improvement is rightly credited to him, as fertility 

 which he has accumulated : the next tenant must 

 regard the same pasture as part of the inherent capacity 

 of the soil. Again, a farmer working on the old four 

 course rotation, selling only corn and meat and purchas- 

 ing neither feeding stuffs nor manures, is dependent on 

 the fertility of the soil : another farmer, carrying on an 

 agricultural business such as market gardening or hop- 

 growing, and putting more into the land every year as 

 manure than he takes out as crop, is only using the 

 land as he would a building, as a tool in a manufactur- 

 ing process. 



Fertility proper is by no means a wholly chemical 

 question, dependent upon the amount of plant food the 

 soil contains; in many cases the physical conditions 

 which regulate the supply of air and water to the plant, 

 and as a corollary, the bacterial life, are far more potent 

 in producing a fertile soil than the mere amount of 

 nutrient material it contains. Especially is this the 

 case in an old settled country like England, where 

 manure is cheap and abundant ; here a fertile soil is 

 often one which is not rich in itself, but one that is 

 responsive to, and makes the most of, the manure 

 applied. Clay soils are not uncommon which show on 

 analysis high proportions of nitrogen compounds and 

 potash, and again no particular deficiency in phosphoric 

 acid, but from their closeness of texture they offer such 

 resistance to the movements of both air and water as to 

 carry very poor crops. Some light soils again, such as 

 those on the chalk, would be regarded on analysis as 

 rich, but they are made so persistently dry by the natural 

 drainage, that only in a wet season do they keep the 

 crop sufficiently supplied with water for a large crop 

 production. On nearly all poor soils it is impossible to 



