134 



COMPOSITION OF SOILS. 



Potatoes 

 Max 

 Beans 

 Barley . 

 Turnips . 

 Oats 



in the same plot 

 in different plots 

 same 

 different 

 same 

 different 

 same 

 different . 



different 



same 



different 



This slio-ws a manifest advantage in shifting crops, varying from 1 to 

 75 per cent ; the deficiency of inorganic matter being the chief cause 

 of difi'erence. As this matter is of great importance to plants, it 

 follo-ws that the composition of soil requires special notice. 



Chemical Composition of Soils. 



Soils have been divided according to the proportion of clay, sand, 

 and lime, -which they possess, into — 



1. Aigillaceous soils, possessing little or no calcareous matter, and 



above 50 per cent of clay. 



2. Loamy soils, containing from 20 to 50 per cent of clay. 



3. Sandy soils, not more than 10 per cent of clay. 



4. Marly soils, 5 to 20 per cent of calcareous matter. 



5. Calcareous soils, more than 20 per cent of carbonate of lime. 



6. Humus soils, in which vegetable mould abounds. 



Below the superficial soil there exists -what is called subsoil, which 

 varies in its composition, and often dififers much from that on th? 

 surface. Into it ■ the rain carries down various soluble inorganic 

 matters, which, when brought to the surface by agricultural opera- 

 tions, as trenching and subsoil ploughing, may [materially promote 

 the growth of crops. The advantages of subsoil ploughing are 

 dependent on the nature of the soil. By means of it the subsoil is 

 loosened, so as to be easily acted upon by air and water, and the 

 efficiency of the drainage is increased. It is not fitted for all soils, 

 and in some instances it may do harm. A knowledge of the chemical 

 as well as mechanical nature of soils guides the agriculturist to a 

 certain extent in his operations ; since, by the judicious application of 

 manures, certain deficiencies may be supplied, and, by admixture, 

 soils may be rendered more suitable for the purposes of vegetation. 



HuMTTS, or decaying woody fibre, called also ulmine, or coal of 

 humus, exists in soik. It is soluble in alkalies, yielding a brown 

 solution, which, when treated with an acid, produces a brown pre- 

 cipitate, said to contain humic, ulmic, and geic acids ; but the separate 



;ja di 



