52 IMPROVEMENT OF SOILS, CONSIDERED 



this may be between two and three feet ; but in pleasure-grounds, where the 

 surface is to be chiefly in grass, nine inches or one foot in depth will suffice. 

 *' It is astonishing," Mr. Rham observes, "how small a portion of pure 

 alumina will consolidate a loose sand, and convert it into a good loam, the 

 parts of which, when moistened, will adhere and form a clod in drying/' 

 (Jour. Ag. Soc. vol. ii. p. 51.) If we take an extreme case, and suppose 

 that any given soil is so sandy as to require the addition of one sixth its 

 bulk of clay, or so clayey as to require one sixth its bulk of sand, then, in 

 the case of kitchen gardens where the soil is three feet deep, every square 

 foot of the clayey surface will require the addition of half a cubic foot of 

 sand ; and in the case of a lawn where the soil is a foot in depth, every 

 square foot of sand will require the sixth of a cubic foot of clay. To cover 

 a statute acre with soil to the depth of one inch requires 121 cubic yards. 

 Hence to add two inches to the soil of a garden of one acre, exclusive of the 

 space occupied by the walks, would require 242 cubic yards or cart-loads, 

 which, at 2s. each, amount to 241. 4s. The cost, however, will depend 

 chiefly on the distance from which the soil is to be brought. A case is 

 mentioned in the Journal of the Agricultural Society of England, vol. ii. p. 67, 

 in \vhich a white sand varying in depth from one to four feet, and so barren 

 that it never had been cultivated to profit, had the surface improved to the 

 usual depth penetrated by the plough (nine to twelve inches), by laying on 

 clay at the rate of 150 cubic yards to the acre. The clay being dug from 

 the subsoil, the expense was not more than 5/. 10*. per acre. It frequently 

 happens that a sandy or gravelly soil is incumbent on a bed of clay, and the 

 contrary ; in either of which cases the supply of the required soil may be 

 obtained by digging pits, or sometimes even by deep trenching. The earth 

 thus obtained will generally be without organic matter, but that can be sup- 

 plied afterwards by manuring. Where the soil required for the improvement 

 of another soil can be obtained in the state of surface soil, the effects produced 

 will be more immediate from the organic matter which such soil contains ; but 

 even when it is obtained from the subsoil, the change in the condition of the 

 soil to which the new soil is applied will soon be rendered obvious ; though 

 not so much the first year, as it will be in two or three years afterwards, 

 when the amalgamation of the two soils is more complete. Much of the 

 effect of adding one soil to another will depend on their intimate mixture; 

 and this can be best effected by repeated trenchings or diggings in dry weather, 

 when both soils are as nearly as possible in a state of dry powder. This point 

 is of great importance, particularly when the soils mixed together contain a 

 good deal of organic matter, because if a very intimate mixture of both soils 

 is not effected, they will, from the difference in their specific gravities, in a few 

 years separate into two different strata. There is, indeed, a constant tend- 

 ency to do this in all soils under culture, and more especially in all such 

 as have been improved by admixture. This takes place in consequence of 

 the softening of the soil by rains, by which the particles are in a manner 

 held for a time in suspension, and the heaviest gradually take a lower place 

 than those which are lighter. Hence the necessity of digging or trenching 

 such soils occasionally to the depth to which they have originally been im- 

 proved. This is required even in artificial soils laid down in grass; for sup- 

 posing a clayey soil to have received a considerable admixture of lime or 

 chalk, and sand, with rotted stable dung, and the whole to have been 

 incorporated hi a state of fallow, and afterwards sown with grass seeds. 



