ROP* 



ON THE ROTATION OF CROPS. 75 



The principles upon which a regular succession of crops is 

 founded, are thus laid down by YVART and PICTET of France, 

 and are given in full in "Chaptal's Chemistry, as applied to 

 agriculture," from which work we make our extracts. 



PRINCIPLE 1. All plants exhaust the soil. [Plants are supported by the earth) 

 the juices with which this is impregnated forming their principal aliment- 

 Water serves as the vehicle for conveying these juices into the organs, or pre- 

 senting them to the suckers of the roots by which they are absorbed; thus the 

 progress of vegetation tends constantly to impoverish the soil, and if the nutri- 

 tive juices in it be not renewed, it will at length become perfectly barren. A 

 soil well furnished with manure may support several successive crops, but 

 each one will be inferior to the preceding, till the earth is completely ex- 

 hausted.] 



PRINCIPLE 2. That all plants do not exhaust the soil equally. Plants are 

 nourished by air, water, and the juices contained in the soil; but the different 

 kinds of plants do not require the same kinds of nourishment in equal degrees. 

 There are some that require to have their roots constantly in water; others 

 are best suited with dry soils; and there are those again, that prosper only in 

 the best and most richly manured land. 



The principal part of the nourishment of the grain crops, 

 and the greater part of the grasses which push up long stalks, 

 in which the fibrous principle predominates, is derived from 

 the ground by their roots, so that these plants exhaust the soil 

 without sensibly repairing the loss. 



Those plants, on the contrary, that are provided with large, 

 fleshy, porous, green leaves, imbibe from the atmosphere car- 

 bonic acid and water, and receive from the earth the other 

 substances by which they are nourished. If these are cut 

 green, the loss of juices, which the soil has sustained by their 

 growth, is less sensibly felt, as a part of it is compensated for 

 by their roots. Nearly all the plants that are cultivated for 

 fodder are of this kind. 



Leguminous plants, such as clover, lucerne, beans, peas, &c., 

 exhaust the soil less than the grains. Their perpendicular 

 roots divide the soil, and their large leaves, and thick, loose, 

 porous stalks, readily absorb air and water. Plants that are 

 cut green, or while in flower, exhaust the soil but little. 



PRINCIPLE 3. That plants of different kinds do not exhaust the soil in the 

 same manner. The roots of plants of the same genus or family, grow in the 

 soil in the same manner; they penetrate to a similar depth, and extend to cor- 

 responding distances; and exhaust all that portion of the soil with which they 

 come in contact. Plants exhaust only that portion of the soil which comes in 

 contact with their roots; and a spindle root may be able to draw an abundance 

 of nourishment from land, the surface of which has been exhausted by short 

 or creeping roots. 



PRINCIPLE 4. That all plants do not restore to the soil the quantity, or the some 

 quality of manure. The plants that grow upon a soil, exhaust more or less of 

 its nutritive juices, but all return to it some remains, to repair part of its loss. 

 The grains and the oleaginous seeds may be placed at the head of those which 

 exhaust the soil the most, and repair the least the injury done it. In those 

 countries where plants are plucked up, they return nothing to the soil that has 

 nourished them. Many plants that are not allowed to produce seed, exhaust 

 the soil but very little; these are very valuable in forming a system of suc- 

 cessive crops, as by introducing them into the rotation, ground may be made 



