SINKING OP MANURES, THROUGH SOILS AND SUB-SOILS. 93 



lost by- sinking through sandy soils, to account for its usually rapid 

 and total disappearance.* 



Aluminous earth, by its closeness, mechanically excludes those 

 agents of decomposition, heat, air, and moisture, which sand so 

 freely admits; and therefore clay soils, in which this earth pre- 

 dominates, give out manure much more slowly than sand, whether 

 for waste or for use. The practical effect of this is universally 

 understood that clay soils retain manure much longer than sand, 

 but require much heavier applications to show as much effect early, 

 or at once. But as this means of retaining manure is altogether 

 mechanical, it serves only to delay both its use and its waste. 



* Except the very small proportions of earthy, saline, and metallic mat- 

 ters that may be in animal and vegetable manures, the whole remainder of 

 their bulk (and the whole of whatever can feed plants) is composed of 

 different elements which are known only in the forms of gases into which 

 manures must be finally resolved, after going through all the various stages 

 of fermentation and decomposition. So far from sinking in the earth, if in 

 quantity, these final results could not be possibly confined there, but must 

 escape into the atmosphere as soon as they take a gaseous form, unless 

 immediately taken up by the organs of growing plants, [or unless held by 

 the soil's absorbing chemical power.] It is probable, however, that but a 

 small portion of any dressing of manure remains long enough in the soil 

 to make this final change ; and that nearly all of it is used by growing 

 plants, during previous changes, or carried off by air and water. [During 

 the progress of the many changes caused by fermentation and decomposi- 

 tion, every portion of the manure fit for use, becomes soluble. When in 

 the soluble state only, it is ready for the use of plants ; and if not then so 

 used, is as ready to be wasted, if the soil has not enough of attracting and 

 combining .power to hold the soluble products. I infer that it depends 

 mainly, if not entirely, on the presence or absence of such chemical power 

 in a sandy soil, with also a sandy or other pervious sub-soil, whether the 

 soluble products of putrescent manures are lost by sinking. If there is 

 not enough such power in the soil (that is, if it contains very little lime 

 in any state)-- and there is too much manure in a soluble state for the roots 

 of growing plants to take up immediately, then the remainder will be dis- 

 solved in the first rain, and follow the course of the excess of water, 

 whether to flow off the surface, or to sink deep into the sub-soil. Of so 

 much as thus sinks, the further decomposition and final conversion to gases 

 must be retarded by the greater seclusion from heat and air. In the mean 

 time, the substance continues to be soluble, and liable to be again carried 

 deeper, by successive heavier rains, until, with their excess of water, pene- 

 trating to the sources of springs, either temporary or permanent, and thus 

 passing into the streams. We know that springs are thus supplied by the 

 rains, and that their waters are in many cases polluted by organic as well 

 as mineral soluble matters. This waste by sinking, even of the fertile 

 parts of natural or unrnanured soil, is manifest on tilled land of which the 

 pervious sub-soil needs and has failed to receive drainage. In such cases, 

 the water below is oozing away after every wet spell ; and sometimes the 

 soil disappears as if washed away, though having nearly a level surface. 

 The dark-coloured organic and alimentary parts only have been thus re- 

 moved, leaving that which had been soil as poor as its sub-soil. 1849.] 



