24 



Rotation of Crops. 



Vol. X. 



Rotation of Crops. 



When a succession of crops is grown upon 

 fertile land without renewal of manure, the 

 produce gradually diminishes; and after a 

 certain period, if it be grain, the quantity 

 which at the outset was eight or nine times 

 the amount of the seed, will be reduced to 

 three times or even to twice the seed. Thus 

 crops impair the fertility of the soil, and 

 eventually exhaust it. 



It has been long admitted, that different 

 species of plants manifest great diversity in 

 tiieir powers of exhaustion. Certain kinds, 

 indeed, as trefoil and lucerne, far from ex- 

 hausting it, communicate new vigor. As a 

 general rule, however, every plant may be 

 said to impoverish the soil in which it grows. 

 This impoverishment is always manifest 

 when the plant after maturity is completely 

 removed, but is less sensible when much 

 rubbish is left. Thus, for example, clover, 

 after yielding two crops, which are gene- 

 rally cut as fodder, might still yield a third; 

 this last, however, is generally ploughed 

 into the ground as manure, being buried 

 along with a considerable quantity of roots. 

 This plan of meliorating tlie soil by the 

 cultivation of trefoil, is what is called ma- 

 nuring by smothering ; a method practised 

 from a remote period in the south of Europe, 

 and which offers decided advantages in those 

 districts where there is abundance of pasture 

 land. Hence, in smothering trefoil, the soil 

 is amended at the expense of the nutritive 

 matter it contains. 



In discussing the advantage of one course 

 of crops over another, the question always 

 hinges upon that of exhaustion. Wherever 

 an unlimited supply of dung and of handi- 

 work can be procured, there is no absolute 

 necessity for following any regular system 

 of rotation. Under such favourable circum- 

 stances it is expedient to ascertain what 

 kind of cultivation is, commercially speak- 

 ing, best suited to the climate and the soil. 

 There is little to fear that by a continued 

 succession of similar crops, the fields will 

 get infested with noxious weeds, because 

 this inconvenience may be obviated by la- 

 bour. Nor is inipoveri.-hment of the soil to 

 be dreaded, since that can be remedied by 

 the purchase of manure. The whole cralt 

 of agriculture is reducible to comparison of 

 the probable value of the crop with the cost 

 of manure, labour, &c. Farming of this 

 sort excludes the keep and propagation of 

 cattle, and may be strictly regarded more 

 as gardening than as agriculture. 



But where manure cannot be had from 

 without, things must be reduced to a sy.?- 

 tem ; and the amount of produce which it 



is possible to export each year is fixed within 

 bounds, which cannot be exceeded with im- 

 punity. 



When by judicious cultivation land is 

 rendered fertile, it is necessary, towards 

 securing its fertility, to supply after every 

 succession of crops equal quantities of ma- 

 nure. In considering this in a purely chemi- 

 cal point of view, it may be said that the 

 produce which can be taken away without 

 damaging the fertility of the land, is the 

 organic matter contained in the crops, ab- 

 straction made of that present in the ma- 

 nure. Indeed, this latter substance must in 

 some form or other return to the soil to fe- 

 cundate it anew. It is capital placed in the 

 ground, the interest of which is represented 

 hy the commercial value of the produce of 

 all the other agricultural operations. 



Where lands are extensive, population 

 scattered, and means of communication diffi- 

 cult, there is less necessity for being tied 

 down to systematic cultivation. There is 

 always enough for a scanty population. A 

 field yields grain, and after the harvest is 

 converted for a series of years into meadow- 

 land ; such is the pastoral system in all its 

 simplicity. To this primitive state of hus- 

 bandry may be referred those plantations on 

 cleared land in countries covered with for- 

 ests. When the trees are felled and burned 

 upon the spot, the soil yields for a long time 

 and without manure, crops of maize and of 

 wheat of surprising quality, at the cost of 

 the fecundity acquired during ages of re- 

 pose. 



But when from increased popiilation the 

 land becomes more valuable, a larger amount 

 of produce is demanded. Imperfect culture 

 would prove inadequate. Accordingly a tri- 

 ennial rotation of crops was very anciently 

 adopted in the north of Europe, consisting 

 as is well known, of fallow land frequently 

 ploughed during summer, followed by two 

 years of grain. The fallow land received a 

 certain quantity of manure to repair the ex- 

 haustion occasioned by the two crops of 

 grain ; hence when this mode of rotation is 

 adopted there should be always sufficient 

 meadow land to supply manure. 



Leaving waste one-third of the surface 

 has always been held a grave objection 

 against triennial rotation. Hence various 

 attempts have been made to get rid of the 

 summer fallow. Some encouragement was 

 given to these attempts from what occurs in 

 horticulture, where the ground is rendered 

 continually productive. In certain coun- 

 tries, moreover, tillage is only interrupted 

 by severe weather. 



On the other hand, it has been long re- 

 marked that it is not always beneficial to 



