IMPROVEMENT OF SOILS CONSIDERED. 



51 



soil is susceptible. Marshy soils are indicated with considerable certainty 

 both by herbaceous and ligneous plants, and also very dry soils ; but the 

 earths of fertile soils cannot be so readily inferred from the plants growing on 

 them. Thus thorn-hedges will be found growing vigorously alike on clays, 

 sands, and chalks ; though never on these soils, or on any other, when they 

 are either very dry, or saturated with water. Some few plants, when found in 

 their native stations in considerable quantities, may be considered absolute 

 in respect to the earths of the soil in which they grow ; such as the Tussilago 

 JParfara, which always indicates clayey soil ; Clematis Vitalba, calcareous soil ; 

 Arenaria rubra, sandy soil ; iiumex Acetosa, ferruginous soil ; Faccinium 

 uligindsum, peaty soil ; Salicornia herbacea, saline soil ; Caltha palustris, 

 marshy soil, &c. : but by far the greater number of plants only indicate the 

 state of a soil relatively to water and organic matter. In short, nature may 

 be said to have only three kinds of soil relatively to plants ; the dry, the 

 moist, and the fertile. 



Sect. II. — The Improvement of Soils, with a View to Horticulture. 



170. Having seen, in the preceding section, that the permanent fertility 

 of a soil depends mainly on its condition relatively to water and heat, it 

 follows that the improvement of soils must be principally directed to increase 

 their capacity for absorbing and retaining these elements in the degree most 

 suitable for vegetation. The principal operations for tliis purpose are : draining, 

 to withdraw superfluous water from soils ; and mixture and pulverization for 

 improving their texture, in order to admit more readily the moisture and the 

 heat of the atmosphere. 



171. Draining is the principal means for altering the condition of a soil 

 with reference to water. Soils are affected by rains from above and springs 

 from below ; and the former are carried off by open gutters, and the latter 

 by covered channels. All draining is founded on the well-known hydrostatic 

 law by which all fluids have a constant tendency to arrange themselves 

 in a horizontal position. Hence, to carry off water, either from a surface or 

 a subsoil, it is only necessary to form channels above or under ground in 

 an inclined position. The kind of drains, and the number employed in any 

 given case, will depend on the texture of the soil and the inclination of the 

 surface. Flat surfaces and retentive clays require the greatest number of 

 drains, and inclined surfaces and porous soils the smallest number. There 

 are very few soils that may not be improved by draining ; and it is 

 almost umaecessary to observe, that, where draining is requisite and not 

 performed, the application of other modes of improvement will be made in 

 vain. 



172. Altering the texture and composition of soil by the addition of other 

 soils is the improvem^ent next in importance to that of draining, and requires 

 only to be mentioned to be understood. Too sandy soils will be improved 

 by the addition of clay, and the contrary ; and both clay and sand by the 

 addition of lime ; because without alkaline matter no soil can be permanently 

 fertile. Though on a large scale the expense of this kind of improvement is 

 too great to be generally adopted, yet in the case of the grounds of small 

 country residences it is practicable at a moderate expense. To ascertain the 

 proportion of one soil that must be added to any other soil so as to perfect 

 its texture, can only be determined by experiment. The first thing to fix 

 on is the depth to which the soil is to be cultivated. In kitchen gardens 



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