CHEMISTRY OF MAMJRES 177 



ment-holder can keep a record, by lettering his fields 

 and plots on a plan of the holdings, of the necessary- 

 change of crop which will give the soil the advantage it 

 would enjoy in a state of nature. This does not mean 

 that rotation goes on in nature, as vegetation there com- 

 pletes a perfect circle within itself for each plant on the 

 spot where it grows, whereas mankind, in robbing the 

 soil of so much starch, sugar, etc., and being rather careless 

 about putting its equivalent back again, must find a ready 

 method of ensuring soil health. This is done in part by 

 the rotation system, as soil formation and the provision 

 of soluble salts go on interminably, and one crop will 

 leave behind the bulk of the minerals and salts suitable 

 for another crop, which can therefore follow it, but the 

 balance must be made up by manuring. 



Corn land exacts the greatest toll of plant food from 

 the soil, and so requires the largest amount of manure. 

 As a matter of fact wheat will grow on ground that is 

 merely well tilled, but not manured, but then the yield 

 in no way compares with ground that has just been under 

 clover or vetches and is tilled and dressed with guano or 

 sulphate of ammonia. 



Clover or green crops should follow wheat or other corn 

 to hearten the ground up again. Dung can now be applied 

 for greens, or for clover give guano, soot or nitrate. The 

 next crop may be roots, such as mangold, turnip, swede 

 or potato, with winter-dunging to ensure complete incor- 

 poration with the soil. The following year the ground 

 may be cleared, given a light dung dressing or else super- 

 phosphate or bones with potash, and beans may be gTown. 

 The fifth year should see a fallow, i.e. a resting year when 

 the ground is sown with lucerne, vetches, turnips or 

 mustard, to form eventually a green manure. Sheep are 

 often run on to the ground in order that a certain amount 

 of forage and soil enrichment may be got at one and the 

 same time, after which the crop is ploughed in. Soil 

 thus treated completely renews its youth, although in 



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