S32 SCIENCE OF AGRICULTURE. Part II. 



with recent dung, immediately finds sufficient soluble matter for its nourishment; and 

 the heat produced in fermentation assists the germination of the seed and the growth of 

 the plant. If, after turnips, barley with grass-seeds is sown, then the land, having been 

 little exhausted by the turnip crop, affbrds tlic soluble parts of the decomposing manure 

 to the grain. The grasses, rye-grass, and clover remain, which derive a small part only 

 of their organised matter from the soil, and probably consume the gypsum in the manure 

 which would be useless to other crops : these plants, likewise, by their large systems of 

 leaves, absorb a considerable quantity of nourishment from the atmosphere, or probably 

 retain the nutritive qualities in the soil, for a covering of slates or any other covering 

 would have nearly the same eifect ; and when ploughed in at the end of two years, the 

 decay of their roots and leaves affbrds manure for the wheat crop ; and at this period of 

 the course, the woody fibre of the farai-yard manure, which contains the phosphate 

 of lime, and the other difficultly soluble parts, is broken down : and as soon as the most 

 exhausting crop is taken, recent manure is again applied. Peas and beans, in all 

 instances, seem well adapted to prepare ground for wheat ; and in some rich lands 

 they are raised in alternate crops for years together. Peas and beans contain a small 

 quantity of a matter analagous to albumen ; but it seems that the azote, which forms a 

 constituent part of this matter, is derived from the atmosphere. The dry bean-leaf, when 

 burnt, yields a smell approaching to that of decomposing animal matter ; and in its de- 

 cay in the soil, may furnish principles capable of becoming a part of the gluten in wheat. 

 Though the general composition of plants is very analogous, yet the specific difference in 

 the products of many of them, prove that they must derive different materials from the 

 soil ; and though the vegetables having the smallest system of leaves will proportionably 

 most exhaust the soil of common nutritive matter, yet particular vegetables, when their 

 produce is carried off", will require peculiar principles to be supplied to the land in which 

 they grow. Strawberries and potatoes at first produce luxuriantly in virgin mould, 

 recently turned up from pasture ; but in a few years they degenerate, and require a fresh 

 soil. Lands, in a course of years, often cease to afford good cultivated grasses ; they 

 become (as it is popularly said) tired of them ; and one of the probable reasons for this 

 is, the exhaustion of the gypsum contained in the soil." " Experience," Mr. Main, the 

 editor of the British Farmer's Magazine, observes, " has proved that land, whatever may 

 be its quality, should not be sown with clover at shorter intervals than five years." 



22 1 9. The power of vegetables to exhaust the soil of the principles necessary to their 

 growth, is remarkably exemplified in certain funguses. Mushrooms are said never to 

 rise in two successive seasons on the same spot ; and the production of the phenomena 

 called fairy rings has been ascribed by Dr. Wollaston to the power of the peculiar fungus 

 which forms it, to exhaust the soil of the nutriment necessary for the growth of the 

 species. The consequence is, that the ring annually extends ; for no seeds will grow 

 where their parents grew before them, and the interior part of the circle has been ex- 

 hausted by preceding crops ; but where the fungus has died, nourishment is supplied for 

 grass, which usually rises within the circle, coarse, and of a dark green colour. 



2220. A rotation is unnecessary, according to Grisenthwaite ; and, in a strict chemical 

 sense, what he asserts cannot be denied. His theory is a refinement on the common 

 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 ( I st, 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 the same cannot be said of garden productions in general, which 

 are very numerous ; 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 potato may be grown successively in the same soil, and produce annually, the effects 

 of climate being excepted, as dry and well flavoured tubers, or nearly so, as they generally 

 produce 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; 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, accm-ately 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 suflSciently advanced in that branch of 

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



