ROTATION. 843 



keep and propagation of cattle, and may be strictly regarded morfe 

 as gardening than as agriculture. 



But where manure cannot be had from without, things must be 

 reduced to a system ; and the amount of produce which it is possi- 

 ble to export each year is fixed within bounds, which cannot be ex- 

 ceeded with impunity. 



When by judicious cultivation land is rendered fertile, it is ne- 

 cessary, towards securing its fertility, to supply after every succession 

 of crops equal quantities of manure. In considering this in a purely 

 chemical point of view, it may be said that the produce which can 

 be taken away without damaging the fertility of the land, is the or- 

 ganic matter contained in the crops, abstraction made of that present 

 in the manure. Indeed, this latter substance must in some form or 

 other return to the soil to fecundate it anew. It is capital placed in 

 the ground, the interest of which is represented by the commercial 

 value of the produce of all the other agricultural operations. 



Where lands are extensive, population scattered, and means of 

 communication difficult, there is less necessity for being tied down to 

 systematic cultivation. There is always enough for a scanty popu- 

 lation. 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 husbandry may be referred 

 those plantations on cleared land in countries covered with forests. 

 When the trees are felled and burned upon the spot, the soil yields 

 for long and without manure, crops of maize and of wheat of sur- 

 prising quality, at the cost of the fecundity acquired during ages of 

 repose. 



But when from increased population the land becomes more valu- 

 able, a larger amount of produce is demanded. Imperfect culture 

 would prove inadequate. Accordingly a triennial rotation of crops 

 was very anciently adopted in the north of Europe, consisting as is 

 well known of fallow land frequently ploughed during summer, fol- 

 lowed by two years of grain. The fallow land received a certain 

 quantity of manure to repair the exhaustion 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 encourage- 

 ment was given to these attempts from what occurs in horticulture, 

 where the ground is rendered continually productive.* In certain 

 countries, moreover, tillage is only interrupted by severe weather. 



On the other hand, it has been long remarked that it is not always 

 beneficial to grow grain during several consecutive years in the 

 same ground, even when it is fertile and manure is abundant, owing 

 to the almost insurmountable difficulty of destroying weeds. The 

 fallow was justly considered the most efficient and economic means 

 of getting rid of these. For this ^pmpose fallow-crops^ as they were 



• Thaer, Agricaltnre ndsonn^e. 



