322 SCIENCE OF AGRICULTURE. Part II. 



Sect. V. Of the Improvement of Soils. 



2162. Soils may be rendered more fit for answering the purposes of vegetation by pul- 

 verisation, by consolidation, by exposure to the atmosphere, by an alteration of their 

 constituent parts, by changing their condition in respect to water, by changing their 

 position in respect to atmospherical influence, and by a change in the kinds of plants 

 cultivated. All these improvements are independent of the application of manures. 



SuBSECT. 1. Pulverisation. 



2163. The mechanical division of the parts of soils is a very obvious improvement, and 

 applicable to all in proportion to their adhesive texture. Even a free silicious soil will, 

 if left untouched, become too compact for the proper admission of air, rain, and heat, 

 and for the free growth of the fibres ; and strong upland clays, not submitted to the 

 plough or the spade, will, in a few years, be found in the possession of fibrous-rooted 

 perennial grasses, which form a clothing on their surface, or strong tap-rooted trees, as 

 the oak, which force their way through the interior of the mass. Annuals and ramen- 

 taceous-rooted herbaceous plants cannot penetrate into such soils. 



2164. The first object of pulvensation is give scope to the roots of vegetables, for with- 

 out abundance of roots no plant will become vigorous, whatever may be the richness of 

 the soil in which it is placed. The fibres of the roots, as we have seen (1538.), take up 

 the extract of the soil by intro-susception ; the quantity taken up, therefore, will not 

 depend alone on the quantity in the soil, but on the number of absorbing fibres. The 

 more the soil is pulverised, the more these fibres are increased, the more extract is ab- 

 sorbed, and the more vigorous does the plant become. Pulverisation, therefore, is not 

 only advantageous previously to planting or sowing, but also during the progress of vege- 

 tation, when applied in the intervals between the plants. In the latter case it operates also 

 in the way of pruning, and by cutting off or shortening the extending fibres, causes them 

 to branch out numerous others, by which the mouths or pores of the plants are greatly 

 increased, and such food as is in the soil has the better chance of being sought after, and 

 taken up by them. Tull and Du Hamel relate various experiments which decidedly 

 prove that, cceteris paribus, the multiplication of the fibres is as the inter-pulverisation ; 

 but the strength of the vegetable, in consequence of this multiplication of fibres, must 

 depend a good deal on the quantity of food or of extract within their reach. The root of 

 a willow tree, as we have seen (1590.), has the fibres prodigiously increased by coming in 

 contact with the water in a river, and so have various other aquatic plants, as alder, mint, 

 iysimkchia thyrsiflora, G^Ua palustris, ffinanthe fistulosa, &c. ; but their herbage is 

 proportionally increased unless the water be impregnated with organised remains. 



2165. Pulverisation increases the capillary attraction, or sponge-like property, of soils, 

 by which their humidity is rendered more uniform. It is evident this capillary 

 attraction must be greatest where the particles of the earth are finely divided; for gravels 

 and sands hardly retain water at all, while clays, not opened by pulverisation or other 

 means, either do not absorb water, or when, by long action, it is absorbed, they retain 

 too much. Water is not only necessary as such to the growth of plants, but it is 

 essential to the production of extract from the vegetable matters which they contain ; and 

 unless the soil, by pulverisation or otherwise, is so constituted as to retain the quantity 

 of water requisite to prodvice this extract, the addition of manures will be in vain. 

 Manure is useless to vegetation till it becomes soluble in water, and it would remain 

 useless in a state of solution, if it so abounded as wholly to exclude air, for then the 

 fibres or mouths, unable to perform their functions, would soon decay and rot off. 

 Pulverisation, in a warm season, is of great advantage in admitting the nightly dews to 

 the roots of plants. Chaptal, in his Agriculture appliquee a Chimie, relates the great 

 benefit he found from the practice, in this respect, to his corn crops ; and shows of what 

 importance it is in the culture of vineyards in France. 



2166. The temperature of a soil is greatly promoted by pulverisation. Earths, Grisen- 

 thwaite observes, are also among the worst conductors of heat with which we are 

 acquainted, and consequently it would be a considerable time before the gradually 

 increasing temperature of spring could communicate its genial warmth to the roots of 

 vegetables^ if their lower strata were not heated by some other means. To remove this 

 defect, which always belongs to a close compact soil, it is necessary to have the land 

 open, that there may be a free ingress of the warm air and tepid rains of spring. 



2167. Pulverisation contributes to the increase of vegetable food. Water is known to be 

 a condenser and solvent of carbonic acid gas, which, when the land is open, can be 

 immediately carried to the roots of vegetables, and contribute to their growth ; but if the 

 land be close, and the water lie on or near its surface, then the carbonic acid gas, which 

 always exists in the atmosphere and is carried down by rains, will soon be dissipated. 

 An open soil is also most suitable for effecting those changes in the manure itself, which 

 are equally necessary to tha preparation of such food. Animal and vegetable substances, 



