CONSTITUENTS OF SOILS. 



71 



phosphate of lime, a second, phosphate of 

 magnesia, a third, an alkali combined with 

 silicic acid, and a fourth, an alkali in com- 

 bination with a vegetable acid. The re- 

 spective quantities of the salts required by 

 plants are very unequal. The aptitude of a 

 soil to produce one, but not another kind of 

 plant, is due to the presence of a base which 

 the former requires, and the absence of that, 

 indispensable for the developernent of the 

 latter. Upon the 'correct knowledge of the 

 bases and salts requisite for the sustenance 

 of each plant, and of the composition of the 

 soil upon which it grows, depends the 

 whole system of a rational theory of agri- 

 culture; and that knowledge alone can ex- 

 plain the process of fallow, or furnish us 

 with the most advantageous methods of af- 

 fording plants their proper nourishment. 



Give so says the rational theory to one 

 plant such substances as are necessary for 

 its developement, but spare those, which are 

 not requisite, for the production of other 

 plants that require them. 



It is the same with regard to these bases 

 as it is with the water which is necessary 

 for the roots of various plants. Thus, 

 whilst one plant flourishes luxuriantly in an 

 arid soil, a second requires much moisture, 

 a third finds necessary this moisture at the 

 cpmmencement of its developement, and a 

 fourth (such as potatoes) after the appear- 

 ance of the blossom. It would be very er- 

 roneous to present the same quantity of 

 water to all plants indiscriminately. Yet j 

 this obvious principle is lost sight of in the | 

 manuring of plants. An empirical system I 

 of agriculture has administered the "same ' 

 kind of manures to all plants ; or when a 

 selection has been made, it was not based 

 upon a knowledge of their peculiar charac- 

 ters or composition. 



The cost of labour in England has given 

 rise to the production of much ingenuity in 

 the invention of machines, which have pro- 

 duced improvements in the mode of appli- 

 cation of manures. In order to use these 

 with advantage, pulverulent manures are 

 employed, instead of the common stable 

 manure, whioh is generally mixed with 

 much straw. 



The necessity for such forms of manure 

 naturally suggested the employment of bone 

 dust, dried dung, lime, ashes, &c. Now, ' 

 although by tnese mean* the necessary 

 phosphates are mrmshed to a soil, and solii 

 animal excrements rendered unnecessary, 

 they have led to the neglect of the liquid 

 excrements, that is, ol the urine of men and 

 animals, which is thus completely lost to 

 agriculture. For although the meadows 

 receive, during autumn and winter, when 

 cattle are fed upon them, the solid and liquid 

 excrements of these animals, yet the urine 

 of man, into which all the nitrogenous con- t 

 stituents of animals are finally deposited, is 

 completely lost to the fields. This most im- 

 portant of all manures, so properly estimated 

 in FlantJers, Germany, and China, is alto- 



gether lost to the English agriculturist. Ir 

 large towns it is either allowed to run into 

 the rivers, or sink into the ground in such a 

 manner as to be of no benefit to the vegeta- 

 ble kingdom. 



The most important growth in England 

 is that of wheat ; then of barley, oats, beans, 

 and turnips. Potatoes are only cultivated 

 to a great extent in certain localities ; rye, 

 beet-root, and rape-seed, not very generall; . 

 Lucerne is only known in a few districts, 

 whilst red clover is found universally. Now, 

 the selection of inorganic manures for these 

 plants may be fixed upon by an examina- 

 tion of the composition of their ashes. Thus 

 wheat must be cultivated in a soil rich in 

 silicate of potash. If this soil is formed 

 from feldspar, mica, basalt, clinkstone, or 

 indeed of any minerals which disintegrate 

 with facility, crops of wheat and barley may 

 be grown upon it for many centuries in suc- 

 cession. But, in order to support an unin- 

 terrupted succession, the annual disintegra- 

 tion must be sufficiently great to render 

 solutle a quantity of silicate of potash suf- 

 ficient for the supply of a full crop of wheat 

 or barley. If this is not the case, the soil 

 must either be allowed to lie fallow from 

 time to time, or plants may be cultivated 

 upon it which contain little silicate of pot- 

 ash, or the roots of which are enabled to 

 penetrate deeper into the soil than corn 

 plants in search of this salt. During this 

 interval of repose, the materials of the soil 

 disintegrate, and potash in a soluble state is 

 liberated on the layers exposed to the action 

 of the atmosphere. When this has taken 

 place, rich crops of wheat may be again 

 expected. 



The alkaline phosphates, as well as the 

 phosphates of magnesia and lime, are ne- 

 cessary for the production of all corn-plants. 

 Now, bones contain the latter, but none of 

 the former salts. These must, therefore, be 

 furnished by means of night-soil, or of 

 urine, a manure which is particularly rich 

 in them.* Wood ashes have been found 

 very useful for wheat in calcareous soils ; 

 for these ashes contain both phosphate of 

 lime and silicate of potash. In like manner 

 stable manure and night-soil render clayey 

 soils fertile, by furnishing the magnesia in 

 which they are deficient. The ashes of all 

 kinds of herbs and decayed straw are capable 

 of replacing wood ashes. 



A compost manure, which is adapted to 

 furnish all the inorganic matters to wheat, 

 oats, and barley, may be made, bv mixing 

 equal parts of bone dust and a solution of 

 silicate of potash (known as soluble gluss in 

 commerce,) allowing this mixture to dry in 

 the air, and then adding 10 or 12 parts ol 

 gypsum, with 16 parts of common salt. 

 Such a compost would render unnecessary 



* It has been already stated that bran contains 

 phosphate of soda and phosphate of magnesia, so 

 that it is useful as a manure where phosphates are 

 desired. ED. 



