ROTATION OF CROPS. 



where they are produced, tend to ren- this healing property, and may be 

 der the soil less productive, or, in the more full of weeds, and no richer 

 language of tanners, to exhaust it. ! when i)loughed up again after a time 

 ""But plants which are sutTered to : than when laid down. Under good 

 decay, or which are consumed by an- management, however, the laying 



imals on the ground on which they j 

 grow, do not e.vliaust the soil. On j 

 the contrary, the decay of the stems 

 and leaves of such jrlants, either nat- 

 urally or hy the consuming of them 

 by animals, tends to add those de- 

 composing organic matters to the 

 soil which form one of the elements 



down of cultivated land to grass and 

 other herbage plants to he consumed 

 upon the ground, is a means of rest- 

 ing the soil and renovating its powers 

 of production ; and this mode of re- 

 cruiting an exhausted soil being al- 

 ways at the conuuand of the farmer, 

 its application is important in prac- 



of its fertility. This process may be 1 tice. It is to be observed, also, that 

 imperceptible and slow, but it is that the poorer soils require this species 

 whichNatureheiself employs to form of rest and renovation more than 



the soil, as distinguished from what 

 has been termed the subsoil. 



" Sometimes this process of decay 

 is counteracted by the singular nat- 

 ural provision of a conversion of the 

 decomposing vegetables into a sub- 

 stance which itself resists decompo- 

 sition, peat. But with this exception, 

 the tendency of the decay of vegeta- 



those which are naturally productive. 

 " The experience of husbandmen, 

 from the earliest times, has shown 

 that the same kinds of plants cannot 

 be advantageously cultivated in con- 

 tinued succession. The same or sim- 

 ilar species tend to grow feebly, or 

 degenerate, or become more subject 

 to diseases, when cultivated success- 



bles upon the surface is to add to the : ively upon the same ground, and 

 fertile matters of the soil. ' hence the rule which forms the basis 



'^This is well understood in the ' of a system of regular alternation of 



|)ractice of agriculturists. When the 

 productive powers of a soil have been 

 exhausted by cultivation and the car- 

 rying away of its produce from the 

 surface, it is laid down to herbage, in 

 which state the future vegetation 

 which it produces tends, by its de- 

 composition upon the surface, to ren- 

 ovate the productive powers of the 

 soil. Land in this state is said to 

 rest. 



" When land, however, has been 

 impoverished by successive crops 



crops is, that plants of the same or 

 similar species shall not be cultivated 

 in immediate succession ; and far- 

 ther, the same rule has been thus far 

 extended, that the same species shall 

 recur at as distant intervals of the 

 course as circumstances will allow. 



"All herbaceous plants, whose pro- 

 duce is carried off the ground which 

 produces them, may be said to ex- 

 haust the soil upon which they grow. 

 But all such plants do not exhau.st 

 the soil in the same degree ; for after 



anil has become full of weeds, the some species the soil is seen to be 

 laying it down to rest in that state [ more impoverished than after others 

 is attended with less beneficial con- 

 sequences than when the soil has 



been previously cleaned of injurious 

 weeds, and fertilized by good culture. 

 In the former case, the process of 

 renovation is sh)w, if perceptible at 

 all ; the useless plants increase, and 

 not those which are beneficial, and 

 afford food to pasturing animals. 

 Land, when properly laid down to 



And not only do ditferent species 

 of plants exhaust the soil in a greater 

 or less degree than others, but the 

 same species does so according to 

 the different period of its growth at 

 which the plant is removed from the 

 ground. 



" When an herbaceous plant is suf- 

 fered to mature its seeds, it exhausts 

 the soil more than when it is removed 



grass, therefore, tends to recover its before its seeds are matured. All 

 wasted powers of production. Land j herbaceous plants, therefore, when 

 not properly laid down has less of I cut in their green state, that is, be- 



669 



