SOIL. 



which exert important influences upon the growth 

 of plants, and the ratios of which it > of the 

 highest importance to the practical farmer to 

 understand. The presence of the substances 

 constantly found in fertile soils in their due pro- 

 S however small these may appear, is 

 just as necessary to maintain fertility, as that 

 of th suhstances existing in the largest propor- 

 tions. All the essential ingredients of a good 

 Mil mut be present to secure a good crop, al- 

 though they need not always exist in precisely 

 the same proportions. Any one of these primary 

 conttituents of soils in superabundant quantity 



SOIL. 



will lessen or destroy fertility. Too much pot- 

 ash, salt, magnesia, iron, lime, or clay, will all 

 impair or entirely destroy productiveness in 

 soils, until these have had the superabundance 

 washed away by rains. The barrenness of a 

 soil may arise from its containing too small or 

 too large a proportion of one or other of the 

 essential ingredients. The proportions of the 

 several inorganic substances required by plants 

 which are the most common objects of culti- 

 vation in England, are presented in the follow- 

 ing table from Prof. Johnston's Lectures. 



Although some of these substances make up 

 comparatively large amount of the ashes of 

 plants, potash composing 23 per cent., and phos- 

 phoric acid nearly one-half the ash of wheat, 

 nets, bmrlejr, and rye, the proportion of these in 

 the soil appears exceedingly small, compared to 

 vhole hulk. How eagerly then must such 

 stibftunces be sought after by the roots of plants 

 appropriated as food ! Straw contains but 

 a VITT small quantity of phosphoric acid. The 

 potash taken up by Indian corn, is in very ' 

 much the same proportion as that abstracted 

 by wheat. The phosphoric acid ascends into the 

 grain, whilst the silicious matter lodges in the i 

 strawor stalk, giving these strength to support the 

 ears. In the potato more than half the ash consists 

 'a*h, whilst the proportion of phosphoric acid ' 



- mall. Thus do plants of various kinds and 

 families differ materially in their demands on the 

 I for sustenance. Kven different parts of the 

 n- plants require various proportions of the nu- 

 itioo* substances. How is it possible for the 

 hcate fibrous roots of plants to derive any 

 nourishment from such hard materials as flint, 

 estom, shells, bones, &c. 7 The answer is 

 these hard substances must all undergo solu- 

 vater before they can be absorbed by de- 

 licate roots and circulated through the infinitely 

 m.n.itf sap-vessels. The perfection of refined 

 nts in knowing how to adapt 

 nth precision the elements requisite as food 

 th* modes of culture necessary in differ- 

 I* to favour in the highest degree the 

 growth and fullest developemont of plants of 

 various descriptions. One of the most impor- , 

 tant points connected with practical farming 

 o be able to specify what particular plants ! 

 take from the soil, and what must be applied 

 in order to restore the deficiency with least 

 exp->- 



Professor J F. W. Johnston has given the I 

 1 1 owing tabular view of the composition of i 

 ^1s of d.fferent degrees of fertility. 



The soil, of which the composition is given 

 in the first column, had produced crops for 60 

 years without manure, and still contained a 

 sensible quantity of all the substances required 

 by plants. That in the second column produced 

 good crops when regularly manured, it teas in 

 want of three or four substances only, which were 

 given to it by the manure. The third was hope- 

 lessly barren, it was in want of many substances 

 which ordinary mamiring could not supply. 



Soils generally have in them some of the ele- 

 ments of fertility so locked up by strong union 

 with other substances, that plants cannot appro- 

 priate them to their uses, unless something be 

 added which has the power to destroy the 

 natural combination, release the fertilizers, and 

 render them accessible to the wants of ve- 

 getables. Under such circumstances, the ap- 

 plication of lime will unlock potash where 

 granite or felspar and mica exist, and the freed 

 potash will in turn render silex soluble. [Sec 

 SILEX, LIME, SALTS.] 



Heavy and stiff clays, which cannot be culti- 

 vated in grain crops to profit, will often pay 

 well for grazing purposes. 



