844 ROTATrON. 



called, were intrDcIuced. Peas, beans. vetcheS; were at first tht 

 only plants used as fallow-crops. 



However, it was soon perceived that the fallow-crops occasioned 

 a very sensible diminution in the produce of corn ; to counteract 

 this inconvenience recourse was had to a surcharge of manure ; but 

 as this cannot always be obtained, it was necessary either to reduce 

 the cultivated surface or to appropriate a certain amount of meadow. 

 Still the fallow-crops had this advantage, that they enabled the farm- 

 er to derive from land a greater amount of produce in a given time 

 without prejudice to the raising of corn. Hence the plan of turn 

 ing the fallow to account was soon generally adopted. 



The introduction of clover so modified the system of fallow-crops 

 as at one time to induce the belief that the point of perfection had 

 been attained in agriculture.* This was when it was ascertained 

 that trefoil, which had hitherto been only cultivated in small enclo- 

 sures, might be sown in spring upon corn land, and occupy next 

 year the place of the fallow in the triennial rotation. Trefoil, so far 

 from exhausting the soil, was found to give it new fertility, and the 

 succeeding corn crop yielded a plentiful harvest. 



It may be easily conceived what advantages were expected in 

 substituting for the unproductive fallow the cultivation of a plant 

 which did not impoverish the land, and furnished a quantity of ex- 

 cellent fodder that served as food for an additional number of cattle. 

 It was even alleged that this plant cleared the fields of weeds. 



A few years' experience sufficed to show that trefoil did not pos- 

 sess all the advantages attributed to it. On renewing the clover 

 every third year on the same piece of ground it sometimes failed. 

 Schubarth, the most zealous and enlightened advocate for its use, 

 limited the renewal of the artificial meadow at first to the sixth, and 

 eventually to the ninth year ; and finding that it did not completely 

 destroy the weeds in corn, he had recourse to hoed-crops for that 

 purpose. 



The introduction of trefoil has gradually led to the system of al- 

 ternate rotation of crops generally adopted at present ; and more- 

 over, contrary to the anticipations of Schubarth, it may be renewed 

 every four or five years on the same parcel of land. 



The impossibility of substituting trefoil for the fallow of the trien- 

 nial rotation was offered as a fresh proof of the principle maintained 

 from time immemorial by agriculturists, namely, that diflferent species 

 of plants should be cultivated in succession on the same land, and 

 that the same species should not recur except at considerable in- 

 tervals ; the earth yielding much finer crops when the same species 

 do not follow in immediate sequence. f 



Attempts have been made at various times to explain this pheno- 

 menon. It was at first thought that different species of vegetables 

 required a particular nutriment ; but it was soon perceived to be 

 otherwise, and that the organs of each plant derived the necessary 

 juices from substances which cone (r in the nutrition of vegetables 



 Thaer, Africttlture ral»oiui*e. t Wd. 



