SOILS— THEIR IMPROVEMENT. 



277 



too much moisture, and occasions a loss of heat 

 by evaporation. But, on the other hand, sur- 

 faces with a considerable inclination towards the 

 south are much more highly heated by the sun's 

 rays than those that are flat, because they are 

 placed at a better angle of elevation for action 

 of the sun's rays upon them. " If the actual 

 increase of temperature produced by the per- 

 pendicular rays of the sun beyond the tempera- 

 ture in the shade be between 45° and 65°," as 

 has been computed by Schiibler to be often 

 the case in clear summer days, this increase 

 would be only half as great if the same light 

 spread itself in a more slanting direction over a 

 surface twice as large. Hence it is sufficiently 

 explained why, even in our own climate, the 

 heat so frequently increases on the slopes of 

 mountains and rocks which have an inclination 

 towards the south. 



§ 3. — THEIR IMPROVEMENT. 



All soils are capable of improvement, so as to 

 render them more fit for the purposes of remu- 

 nerative cultivation. The principal operations in 

 connection with this are draining, pulverisation, 

 consolidation, alteration of their constituent 

 parts, exposure to atmospheric influence, &c. 



Draining is the first and principal means of 

 improving a soil, and without it all other at- 

 tempts will prove of no avail. The number and 

 form of drains will depend on local circum- 

 stances, of which the texture of the soil is by 

 no means the least worthy of careful study. The 

 leading or main drains in gardens should inva- 

 riably be placed under the walks, and the over- 

 flow drain carried beyond the enclosed bound- 

 ary. With this drain all the others should 

 communicate. The depth of drains will depend 

 on local circumstances, but it is better that 

 they be deep than otherwise, so that they may 

 not be disturbed by trenching or other excava- 

 tions. Those in connection with the cellars, 

 stoke-holes, &c, should be sufficiently deep 

 to thoroughly clear them of water; and in 

 their first formation they should be laid even 

 to a greater depth, to provide against the chance 

 of sinking either the one or the other at a future 

 time. 



The principal drains in a garden, as well as in 

 all dressed grounds, should be laid down in the 

 most substantial manner possible, in the first 

 instance, and their lines correctly marked on a 

 plan upon a large scale, that they may be easily 

 got at in case of accident, and their direction 

 should be such as to come under permanent 

 buildings, &c. as seldom as possible. Without 

 due attention to these points, much trouble 

 and expense may be incurred, besides the de- 

 rangement attendant on breaking up the ground 

 afterwards. Main drains often offer a conve- 

 nient entrance for rats and other vermin ; their 

 mouths should be guarded with efficient iron 

 gratings ; and as a farther precaution, drain-traps 

 should be placed in them at convenient dis- 

 tances. — {Vide vol. i., Sect. Tanks.) 



There is no operation in the whole catalogue 

 of improvements in which so much gross igno- 

 VOL. II. 



ranee has been displayed as in that of draining ; 

 and, in many cases, strict adherence to the 

 dicta laid down by professed drain-doctors has 

 amounted to time and capital thrown away. A 

 universal system of draining in all soils, and 

 under all circumstances, is about as unreason- 

 able as a universal medicine to be administered 

 for all diseases, and to all ages, sexes, and con- 

 stitutions. 



The advantage of draining is twofold : the 

 first is the elevating the temperature of the soil 

 by the abstraction of superfluous moisture, and 

 hence admitting the rays of heat to occupy those 

 spaces formerly charged with water; — the soil thus 

 becomes warmed by conduction ; and the atmo- 

 sphere above, by a diminution of evaporation. 

 Air, from which the roots of plants derive so 

 much advantage, is admitted to them, the soil 

 and atmosphere above it becoming materially 

 changed for the better. So important a matter 

 is this, in relation to horticulture, that many 

 now form their borders for their finest fruit- 

 trees' upon the top of vaults kept constantly 

 filled with air ; and few exotic fruit-houses are 

 now built without abundance of subterranean 

 ventilation being provided. In wet districts, 

 and where the subsoil is a close tenacious 

 clay, the process of vaulting might be carried 

 over the surface of a large garden, and with 

 the most beneficial effects. Next to that would 

 be the formation of a bed of loose stones, 

 scoriae, or other similar material, between the 

 soil and subsoil, not only to act as a general 

 drainage, but also as a means of admitting air to 

 the roots of plants. In such a stratum drain- 

 tiles should be laid in lines 6 or 8 feet asunder, 

 and made to communicate with cross ones, 

 which latter should have a free communication 

 with the external air. On wet clayey retentive 

 subsoils, this would, next to vaulting over the 

 whole area, be the most effectual means of 

 thoroughly improving the soil, so far as the ad- 

 mission of air and the abstraction of water are 

 concerned. The temperature of a heavy soil in 

 a garden in Hampshire has been raised 15° by 

 drains 4 4 feet deep. Drainage not only permits 

 the heat to penetrate deeper into the soil, but it 

 also enables it to retain it a longer time. Mr 

 Shearer has clearly shown the effect of vaulting, 

 which is drainage carried to its fullest extent, in 

 the case of the fruit-tree borders in the gardens 

 atYester — a cold locality, at the base of the Lam- 

 mermuir range— to be equal to 9° of increased 

 temperature — (Vide vol. i. p. 31.) 



Now, in all naturally cold countries, whatever 

 tends to increase the temperature of the air or 

 of the soil must be regarded as being of the 

 utmost importance to vegetation ; and as drain- 

 ing produces this effect, its importance must be 

 of the greatest consequence to man, and that 

 importance increases as we recede from the 

 equator. For, although exactly the same depth 

 of rain should fall annually in lat. 1° south that 

 falls in lat. 50° north, the soil in the latter will 

 be many times wetter than in the former, on 

 account of a greatly diminished amount of eva- 

 poration, in consequence of our greater distance 

 from the sun. The importance of draining has 

 of late years been fully acknowledged; and 



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