SOILS-THEIR IMPROVEMENT. 



279 



formed by the decomposition of the enclosed 

 air. The advantages of the heat thus obtained 

 in exciting vegetation, whether in a seed or root, 

 especially in spring, when the soil is cold, must 

 be very considerable." By a judicious system 

 of trenching, fresh soil will be brought into im- 

 mediate contact with the roots of plants — a cir- 

 cumstance of so much importance in culture, 

 and so well known, as to require no further com- 

 ment. " The free admission of atmospheric air 

 to soil is also necessary for the decomposition of 

 humus, or organic matter, by which carbonic 

 acid is formed. The atmospheric air is also a 

 great source of nitrogen, which has been lately 

 found in all plants, and more especially in the 

 spongioles of the roots. The soil also, when 

 loosened, becomes a rapid conductor of water; 

 and supposing the texture of the soil to be suit- 

 able for culture, it will retain a sufficient quan- 

 tity of moisture for the purpose of vegetation, 

 and allow the escape of what is superfluous by 

 filtration into the subsoil, or into the under- 

 ground drains which have been formed as a sub- 

 stitute for a porous substratum. The mere act 

 of pulverising any soil has a tendency to improve 

 its texture, more especially if the operation be 

 frequently repeated. In summer, by exposure 

 of a soil to the air, the particles are separated by 

 the evaporation of the water in their interstices 

 by heat ; and by exposing a soil to the frosts of 

 winter, the particles are separated by the expan- 

 sion of the water in the act of freezing. Clayey 

 soils containing iron are in an especial manner 

 improved by exposure to the atmosphere, the 

 iron being still further oxidised, and thus acting 

 like sand in separating the particles, as well as 

 being less likely to be rendered soluble by the 

 addition of saline matters." — Sub. Hort., p. 55. 



Jethro Tull, one of our earliest writers on im- 

 proved husbandry, estimated the process of 

 pulverisation so highly, that he fancied no other 

 assistance was required in the preparation of the 

 soil for crops; in this, however, he overrated 

 this important operation. Du Hamel, entertain- 

 ing somewhat similar views with Tull, decidedly 

 proved that the multiplication of the fibres of 

 plants is as the inter-pulverisation of the soil ; 

 but the advantages thus gained by vegetables, 

 by the increased number of their fibres, must 

 depend a good deal on the quantity of food 

 within their reach. However much the two 

 authorities last quoted may have overrated pul- 

 verisation, one thing is certain, that where it is 

 carried out to its fullest extent, the quantity of 

 manure required is very materially lessened. 

 Nevertheless, as garden soils require to be 

 loosened to a considerable depth, to allow the 

 roots of many plants to descend, it also follows 

 that enrichment should be carried to the same 

 extent, and the more so when we consider that 

 the roots of all plants collect their nourishment 

 from their extreme points, and that many of 

 them, such as beet, parsnip, &c, derive then- 

 food at a depth of 2 or 3 feet below the surface. 



Digging, ridging, and trenching. — These are 

 important operations, performed, in general, only 

 by commercial growers, who have to make the 

 most of their ground ; and as they carry out 

 these to a great extent, it is quite evident that 



they see the propriety of so doing. In private 

 gardens they are much neglected ; and hence 

 one of the causes why the productions in them 

 are so inferior to the others. In ordinary dig- 

 ging, the spades used in the market-gardens 

 around London are 134 inches long and 10 

 inches broad, while those used in private gar- 

 dens are seldom more than 10 inches by 74 

 inches, the former loosening the ground to a 

 greater depth. Nor is even this deemed suf- 

 ficient; almost every portion of ground is single 

 or double trenched annually. 



Garden spades are of various forms, and 

 adapted to various purposes ; but, until of late 

 years, little improvement has been made in 

 them. For all purposes of lifting the soil, or 

 digging pits, they are better than forks; but for 

 the mere purpose of pulverising by loosening, and 

 for digging up roots, and digging amongst plants 

 and trees, broad-pronged forks are preferable. 



Lindon's cast-steel spade is the best: the 

 blade is thinner, yet stronger, than the garden 

 spade in ordinary use, thus constituting an im- 

 portant point in its favour, because one-third 

 less power is required to force this thin-bladed 

 tool into the ground than the thick and clumsy 

 spade hitherto used. The handle, also, in Lin- 

 don's spade is improved by being curved a little 

 forward, giving it a better leverage than if it 

 were straight, and rendering less stooping neces- 

 sary in using it. The blade is highly tempered, 

 which renders it an excellent cutter of roots, 

 working clean, and wearing well. It is known 

 also as the Birmingham spade. 



Black's spade is in much repute in Scotland, 

 as being of excellent material. It is very similar 

 to Lindon's in form — scarcely, however, so light, 

 and probably less highly tempered. They are 

 manufactured at Ford Forge, Ford, Northum- 

 berland. 



The sizes of the above spades are, 



No. 2.-7^ in. bd. at bottom, 7J in. at top, and 12 in. deep. 

 No. 3.— 7£ ... 8 12J . 



No. 4.-84 8} 13* . 



No. 5.— 8£ ... 9 13£ . 



No. 6.— 8f 9$ 14 . 



The prong spade. — This implement is much 

 used in some parts of Kent, and also in Che- 

 shire, where it is called a " mule," from the cir- 

 cumstance of its combining, as it were, the com- 

 mon three-pronged fork and the common spade. 

 In form it is a three-pronged fork with a spade 

 handle, the points of the prongs being united 

 together by a slip or strap, about 1 \ inches wide, 

 of steel welded to them, which forms the face 

 or cutting part. It is lighter than the common 

 spade, and well adapted for digging purposes. 



It has been remarked, as one advantage aris- 

 ing from this deep- digging and trenching, that 

 slugs and other insects are comparatively of 

 rare occurrence in such grounds, possibly from 

 their eggs and larvae being buried too deep to 

 become hatched by the solar heat near the sur- 

 face. There can be no doubt, the deeper the soil 

 is dug, the more fitted it is for productive crops ; 

 evaporation is promoted, a free and more ex- 

 tended sphere is offered to the roots, which en- 

 ables them to range farther in search of food, 

 and the soil becomes much less exhausted by 



