SCIENTIFIC AGRICULTURE. 203 



smallest expense. The time which land may lay in pasture 

 and still increase in richness, must have a limit, and this 

 depends upon the quality of the soil and the kinds of grass 

 which occupy it. 



The soil will require an occasional top dressing, or the pas- 

 ture will deteriorate: on account of the exhaustion of certain 

 elements in the soil, grasses, as well as forest trees and other 

 plants, tend to a natural rotation; one species, after flourishing 

 a few years, begins to decline and finally dies out, and is 

 replaced by another, and this, in time by another, and so on, 

 indefinitely. All pasture lands whatever, which are arable, 

 can, after a series of years, be subjected to grain crops; and 

 this in most cases would doubtless be expedient. This how- 

 ever, must be determined in each particular case, by an appre- 

 ciation of all the circumstances and conditions. 



