134 CHEMISTRY OF AGRICULTURE, 



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of the above elements; consequently the soil cannot suit all kinds of 

 plants while it may be well adapted to particular kinds. Hence the 

 importance of a rotation of crops requiring these elements in different 

 proportions. One kind of soil, it will be seen, may ripen the straw 

 and not the ear, or the ear and not the straw, 



The amount of inorganic matter required for the crops of 4 years, 

 per acre say 1st year 25 tons of turnips and 7 tons ol the tops ; 2nd 

 year 38 bushels of barley and 1 ton of straw ; 3d 2 tons of clover 

 and rye-grass, and 4th 25 bushels of wheat and 13 tons of straw, 

 would thus be 12.40 Ibs. in the following proportions : pot-ash 

 281 Ibs. ; soda 130 Ibs; lime 242, magnesia 42, alumina 11, silica 

 318, sulphuric acid 111, phosphoric acid 61, and chlorine 39 Ibs. Ac- 

 cording to this it is supposed that, to restore these elements to the soil 

 by manuring or otherwise, each acre requires, every 4 years, pearl or 

 pot-ash 390 Ibs ; carbonate of soda 440 Ibs. ; common salt 65 Ibs. ; 

 burned lime 240 Ibs. ; epsom salts 250 Ibs. ; alum 84 Ibs. ; bone dust 

 280 Ibs. 



The importance of liquid manures from the farm yard will be appa- 

 rent for some of these constituents. Some soils or sub-soils, however, 

 contain, no doubt, a general supply of these substances, and the 

 elaboration of the elements obtained from the air also furnishes some 

 of them ; hence the waste is not readily perceived, while other soils 

 are soon exhausted. A century even may not exhaust these substan- 

 ces, but a gradual, if not rapid, diminution of them must take place. 



Of the organic portion of soils, we have said vegetable and animal 

 remains constitute the chief substances. These vary greatly, and 

 are furnished by vegetables decaying upon them, by manures or by 

 streams of water. This is the humus before spoken of. In peaty 

 soils they are said to constitute, oftentimes, from 50 to 70 per cent., by 

 weight. Rye and oats grow on soil which contains but 1 per cent., 

 while wheat soils contain from 4 to 8 per cent., and in very clayey 

 and stiff soils 10 or 12 per cent, is sometimes found. The upper soil 

 is said to be often overloaded in very old pastures and gardens. The 

 humus thus furnished the soil by the decay of organic matter, is of 

 the first importance. The animal matter chiefly supplies the ammonia 

 and nitrogen, so important in plants. 



The inorganic matter before noticed, consists of soluble or saline 

 substances and insoluble or earthy substances. Thus, if the soil 

 be dried in an oven, and a pound of it well stirred in 1J pints of pure 

 boiling rain water, the liquor allowed to settle and then is poured off 

 or boiled away, a portion of saline matter will remain, which may be 

 from 2 to 20 grains. This is the soluble matter or portion of the 

 soil, and consists commonly of sulphate of soda or glauber salts, com- 

 mon salt, sulphate of magnesia, or epsom salts, with small portions 

 of chlorides and nitrates, which are detected by chemical tests. 



