I 



Book III. MANURES. 327 



idea of the uses of a rotation stated above ; but by giving some details of the constituent 

 parts of certain grains and certain manures, he has presented it in a more clear and 

 striking point of view than has hitherto been done. To apply the theory in every case, 

 the constituent parts of all manures and of all plants (1st, their roots and leaves, and 

 2dly, their seeds, fruits, or grains,) must be known. In respect to manures this is the 

 case, and it may be said to be in a great degree the case as to the most useful agri- 

 cultural plants; but, unfortunately for our purpose, the same cannot be said of garden 

 productions in general, though no branch of culture can show the advantage of a rota- 

 tion of crops more than horticulture, in the practice of which it is found that grounds 

 become tired of particular crops, notwithstanding that manures are applied at pleasure. 

 If the precise effects of a rotation were ascertained, and the ingredients peculiarly neces- 

 sary to every species pointed out, nothing could be more interesting than the results of 

 experimental trials ; and whoever shall point out a simple and economical mode by which 

 the potatoe may be grown successively in the same soil, and produce annually, neglecting 

 tlie effects of climate, as dry and well- flavored tubers, or nearly so, as they generally pro- 

 duce the first and second years on a new soil, will confer a real benefit on society. That 

 wheat may be grown many years on the same soil by the use of animal manures, or such 

 as contain gluten, Grisenthwaite's theory would justify us in believing chemically ; and it 

 ought to be fairly tried by such cultivators as Coke and Curwen, Till this is done in 

 the face of the whole agricultural world, and the produce of every crop, and all the par- 

 ticulars of its culture, accurately reported on annually, the possibility of the thing may 

 be assented to from the premises, but will not be acted on ; and, in fact, even the best 

 agricultural chemists do not consider that we are sufficiently advanced in that branch of 

 the science to draw any conclusion, a priori, very much at variance with general opinion 

 and experience. It should always be kept in mind, that it is one thing to produce a 

 crop, and a different thing to grow crops with profit. 



2158. The principles of rotations of crops , are thus laid down by Yvart and Ch. Pictet 

 (Cours complet d' Agriculture, articles Assolement, and Succession de Culture ; and Traiti 

 des Assolemens. Paris, 8vo. 



The first principle, or fundamental point is, that every plant exhausts the soil. 

 The second, that all plants do not exhaust the soil equally. 



The third, that plants of different kinds do not exhaust the soil in the same manner. 

 The fourth, that all plants do not restore to the soil the same quantity, nor the same quality of 

 manure. 

 The fifth, that all plants are not equally favorable to the growth of weeds, 



2159. Thefolloiving consequences are drawn, from these fundamental principles : 



First. However well a soil may be prepared, it cannot long nourish crops of the same kind in succession, 

 without becoming exhausted. 



Second. Every crop impoverishes a soil more or less, according as more or less is restored to the soil by 

 the plant cultivated. 



Third. Perpendicular rooting plants, and such as root horizontally, ought to succeed each other, 



Fanirth. Plants of the same kind should not return too frequently in a rotation. 



Fifth. Two plants favorable to the growth of weeds, ought not to succeed each other. 



Sixth. Such plants as eminently exhaust the soil, as the grains and oil plants, should only be sown when 

 the land is in good hearty 



Seventh. In proportion as a soil is found to exhaust itself by successive crops, plants which are least ex- 

 hausting ought to be cultivatsd. 



2160. Influence of rotations in destroying insects. Olivier, member of the Institute of 

 France, has described all the insects, chiefly tipulae and muscse, which live upon the collar 

 or crown of the roots of the cereal grasses, and he has shewn that they multiply themselves 

 without end, when the same soil presents the same crop for several years in succession, 

 or even crops of analogous species. But when a crop intervenes on which these insects 

 cannot live, as beans or turnips, after wheat or oats, then the whole race of these insects 

 perish from the field, for want of proper nourishment for their larva.^ {Mem, de la Societi 

 Roijal et Centrale d Agr, de Paris, vol. vii.) 



Chap. II. 

 Of Manures. 



2161. Everi/ species of mailer capable ofjiromoting the growth of vegetables may be con- 

 sidered as manure. On examining tlie constituents of vegetables, we shall find that 

 they are composed of oxygen, hydrogen, carbon, and nitrogen, or azote, with a small 

 proportion of saline bodies. It is evident, therefore, that the substances employed 

 as manure should also be composed of these elements, for unless tliey are, there will 

 be a deficiency in some of the elements in the vegetable itself; and it is probable 

 that such deficiency may prevent the formation of those substances within it, for which its 



y 4 



