ROTATION OF CROPS 211 



even longer, after which it begins over again in the 

 same order. This rotation of crops is designated 

 according to the number of years the series covers, 

 as for instance a five-year or a six-year rotation. A 

 six-year rotation might run, we will say, somewhat 

 as follows : 



1st year — potatoes — enriching crop. 

 2nd year — wheat — impoverishing crop. 

 3rd year — clover — enriching crop. 

 4th year — wheat* — impoverishing crop. 

 5th year — sainfoin — enriching crop. 

 6th year — oats — impoverishing crop. 



"Let us examine in detail this series that we have 

 taken as an example. The first year the soil is thor- 

 oughly manured. One of the effects of manuring is 

 to start a great crop of weeds that would infest the 

 land and impoverish the crop were they not care- 

 fully removed. Hence the necessity of weeding. To 

 weed a piece of ground is to destroy the weeds either 

 by hand or with some implement. But it is not every 

 crop that admits of weeding: the plants must be a 

 certain distance apart, as otherwise they will be 

 trampled under foot, cut off, or uprooted in the 

 weeding process. Wheat cannot be weeded, its stalks 

 are too close together ; but potatoes are far enough 

 apart for weeding without difficulty. Now, weed- 

 ing destroys all useless, injurious grasses and other 

 unwelcome intruders; their future reappearance is 

 prevented by pulling them up before their seeds 



