r 



236 



^. 



AERATION AND 



der : for the moiil: 



of fo 



as 



Sect. XII. j. 



flliiy for Its being permeated 



by the young roots of plants, as its fmall cohefion, as mentioned in 

 Se£l. X. 3. 6. 



Secondly, a more intimate mixture of the various inc^redients 

 which moft foils poffefs, as carbon, calcareous, argillaceous, filiceous 

 and magnefian earths, with various metallic oxydes, as thofe of iron 



and fometimes of mano-anefe 



o 



d 



m} 



all 



h 



by freq 



turning over the foil with the plough or fpade, become mixed fo as 

 to a6l on each other or on the roots of vegetables in every minute part 

 of th^ foil. 



th 



finki 



incr more 



And thirdly, the vernal rains are retained 

 readily into the pores and cells of land recently turned over, and 

 which fiill poflefles an uneven furface. Befides a greater furface of it 

 being continually expofed to the paffing air, and to the heavier im- 

 purities, which it perpetually contains, as carbonic acid, foot, odours 

 £>f many kinds. 



3. A recapitulation of thefe circumftances leads us to the know- 

 ledge of the ufe of fallowing lands, by repeatedly turnino- them over 

 much carbonic acid is produced in its fluid ftate ; and perhaps fome 

 of the nitrous and phofphoric acids ; thefe may remain united with 

 the vegetable recrements, or with volatile alkali, or with calcareous 

 earth. 2. The parts of the foil may become better mixed too-ether, 

 and thus either chemically affe<St each other to their mutual meliora- 



or they may more uniformly fupply nutriment to the roots. 



tion 



9 



which penetrate it. 3. The foil may become broken into a moift 



powder, and may thus be moreeafily permeated, and fupply a o-reater 

 furface of Its cavities for the vegetable abforbents to apply themfelves 

 to. 4. Unprofitable plants, or weeds, not being permitted to grow on 



their early 



it, or their being perpetually ploughed under the foil in 

 growth, much vegetable nutriment will be referved by not being ex- 

 pended ; or It will be increafed by the faccharlne and mucilaginous 



matter of the young plants, which are thus buried in it. 



It 





