ing portions are still rich in them. If, therefore, a suc- 

 ceeding crop is to grow equally well on all parts of a field, 

 there must be a thorough mixing of the exhausted and of 

 the unexhausted portions of soil. This is effected by mechan- 

 ical means, by manures, or by certain chemical compounds. 

 Hence the necessity of becoming acquainted with the na- 

 ture and properties of the soil and subsoil. The second 

 chapter is devoted to this subject. 



The soil consists of arable surface soil and subsoil. In 

 the former is accumulated the nutriment of plants chiefly 

 cultivated for the food of man. This* accumulation is 

 affected by the absorptive power of the arable soil for 

 mineral matters, by which soluble salts are removed from 

 solution, and even chemical decomposition of the most 

 stable compounds is brought about, and the bases or acids 

 are retained by the soil in a firm state of combination. It 

 is the presence of food in the soil in this state of phys- 

 ical combination which is alone available for the nutrition 

 of plants. On the abundant or scanty supply of food in 

 this state depends the fertility or sterility of a soil. In 

 fertile soils food is present also in another form, in whicli 

 it is not immediately available for the nutrition of plants. 

 It exists as chemical compounds which are not soluble in 

 water, or acids until rendered so by the action of power- 

 ful chemical agents, or to a much smaller extent by the 

 slower process of the decomposing action of the weather. 

 When the food is eliminated by disintegration (by fallow 

 and mechanical operations) from this inert state of chem- 

 ical combination, it passes into that of physical combination 

 with the earthy particles before it is absorbed by the 

 plant. Each kind of soil has its own absorptive power for 

 causing the food to pass into a state of physical combina- 

 tion. When manure is applied, its greater or less disper- 

 sion throughout the soil will depend on this power. In 

 general it is absorbed and fixed by the upper few inches 



