274 



MANUAL OF AGPJCULTUKE. 



shift rotation on tlie strong clay soils. Wheat, beans, and 

 fallow (either a hare fallow or a green crop) is an example of a 

 three-shift rotation. A fonr-shift rotation practised in Norfolk 

 is wheat, roots, barley, and clover. Of a five-shift, we have as 

 an example, wheat, roots, barley or oats, and grass ("seeds") 

 for two years. The Lothians' six-course is roots, wheat or barley, 

 seeds one year, oats, beans or potatoes, and wheat ; when the land 

 is stiff, the wheat succeeds the roots, and beans the oats ; barley 

 and potatoes respectively being substituted where the ground is 

 of a liohter nature. The following^ six-course shift is observed 

 on some of the heavy alluvial soils of Scotland — fallow, wheat, 

 barley, seeds, oats, and wheat. Of course there are numerous dif- 

 ferent courses of rotation, in addition to the above, according to the 

 difference of peculiarity and requirement, in the various localities 



adonting them. 



Mcmurcs. 



Calculating upon the basis of the figures of the analyses, quoted 

 in the j)receding chapter, an average crop of wheat extracts, per 

 acre, from the soil, inorganic compounds to the following amount: — 



Potash, 



Soda, 



Lime, 



Magnesia, 



A fair crop of beans : — 



Potash, 



Soda, 



Lime, 



Magnesia, 



Phosphoric acid, 



lbs. 

 23 



n 



8 

 6 



lbs. 

 66-1 

 9" 

 44i 

 13 

 33 



Phosphoric acid, 

 Sulphuric acid, 

 Silica, . 

 Oxide of iron. 



Sulphuric acid, . 



Silica, 



Oxide of iron, . 



Chloride of sodinm, . 



Chloride of potassium, 



lbs. 



20 



4 



84 



1 



lbs. 



/ 



18 



^4 



A crop of turnips weighing twenty tons to the acre approxi- 

 mately : — 



Potash, 

 Soda, 

 Lime, 

 Magnesia . 



lbs. 

 145 



28 

 116 



16 



Phosphoric acid, 

 Sulphuric acid, 

 Chlorine, . 



lbs, 

 50 

 65 



80 



And a crop of potatoes weighing eight tons of tubers would 

 extract approximately : 



Potash, . 



Soda, 

 Lime, 

 Macrnesia, 



lbs. 



90 

 8 

 5 

 8 



Phosphoric acid. 

 Sulphuric acid, 

 Chlorine, . 



lbs. 

 20 

 34 

 10 



When clovers and grasses are depastured, only a trifling quan- 

 tity of the inorganic constituents of the soil are removed from 

 it, seeing that they are nearly all returned to the ground in 

 the excreta of the grazing animals. But it is different when 

 they are cut for hay; then the inorganic constituents are 



