92 BRITISH HUSBANDRY. ' [Ch. VII. 



their growth ; and virgin soils, which have been kept under pasture, are 

 generally capable of producing a series of similar crops during a number of 

 years. Under such circumstances, the whole art reduces itself to the choice 

 of those crops which the land will produce with the greatest profit in its 

 actual state, and little fear need be entertained of its exhaustion ; but these 

 are incidents of a nature which do not belong to the ordinary range of 

 cultivation, and which therefore do not fall within the scope of our 

 observations. 



The necessity of supplying the land, when under tillage, with a certain 

 quantity of animal manure, has taught all farmers the expediency of com- 

 bining the production of grain with the support of a certain number of 

 cattle ; by which they are enabled to draw from each all the advantages of 

 which they are susceptible. Upon that point there is but one opinion ; but 

 regarding the reciprocal relation of each to the other, or the relative quan- 

 tity of land which ought to be applied to each, much difference prevails. 

 The various systems of cultivation may be divided into two classes : the 

 one, chiefly confined to the culture of corn ; and the other, comprehending 

 the alternate culture of corn and roots. Under the former, it is abso- 

 lutely necessary to retain a certain portion of meadow and pasture for the 

 maintenance of the stock ; while under the latter, the same object can be 

 effected without the aid of natural grass. The mode of cropping must 

 therefore differ on each, and must depend upon the nature of the land ; 



It is formed from the putrefaction of vegetable and animal matter, and is described as 

 " a dark, unctuous, pliable substance, nearly uniform in its appearance. It is a com- 

 pound of oxygen, hydrogen, carbon, and nitrogen, which — with the exception of nitroj^en, 

 which is found only in some substances — are the elements of all animal and vegetable 

 substances : it is the result of the slow decomposition of organic matter in the earth, and 

 is found in the greatest abundance in rich garden-mould, or old neglected dunghills. 

 It varies somewhat in its fjualities and composition according to the substances from 

 which it has been formed, and the circumstances attending their decajr. It is the product 

 of organic power, such as cannot be compounded chemically." — See the Penny Cyclo- 

 paedia, under the article ' Arable Land.' 



Sir Humphry Davy also thus alludes to it in the following passage of his Fourth Agri- 

 cultural Lecture : — " In most of the black and brown vegetable moulds, the earths seem to 

 be in combination with a peculiar extractive matter aflbrded during the decomposition of 

 vegetables. This is slowly taken up, or extracted from the earths by water, and appears 

 to constitute a prime cause of fertility in the soil." — Quarto, p. 170. 



It may be fairly presumed that the quantity of this humus must be necessarily dimi- 

 nished by the growth of vegetables in proportion to the sap which they extract from the 

 soil, and that its diminution must be equal to the amount of nutritive matter which they 

 contain. This is indeed proved by experience in the case of corn ; for wheat is known 

 to exhaust the land more than rye ; rye more than barley ; and barley more than oats ; 

 and experiments which have been carefully made by analysis of those species of grain 

 show that, when of ordinary quality, they respectively contain the following proportions 

 per cent., of gluten, starch, and mucilage, of which this nutritive substance is composed, 

 namely — 



Wheat, 78 per cent. Barley, 65 per cent. 



Rye, 70 ,, Oats, 58 ,, 



Thus, having regard also to some differences in the nutritive value of the straw — 

 A bushel of Wheat, weighing 591bs., would absorb about 4filbs. of nutritive matter. 

 3 J "ye , , 55 , , 38^ , , 



, , Barley , , 46 , , 30* , , 



., Oats ,,34 ,, 20' ,, 



Supposing this view of the subject to be correct, the result of these experiments would 

 show that the different grain-crops exhaust the soil in the relative proportions above 

 stated: and admitting season and culture to be the same, we must tlierefore conclude 

 that if the qualities of humus are in every respect equally effectual in promoting vegeta- 

 tion, its effects will be visible in the crops ; consequently, that if any one of them be 

 unusually abundant, the succeeding one must be proportionably deficient, — See ThUer, 

 ' Principes Raisonnes d'Agric,,' torn. i. p. 254. 



