ROTATION OF CROPS 191 



same species as had in the previous year 

 occupied the field. When a crop of red 

 clover is removed from the land, it is found 

 that wheat thrives vigorously upon the 

 decaying roots of the clover ; while the 

 leaves of the turnip crop that are left upon 

 the land have a markedly beneficial effect 

 upon a crop of cereals that may follow. If 

 any one doubts the fertilizing value of 

 turnip leaves one has only to look over a 

 cereal crop which has followed a root crop, 

 where the bulbs were topped and where the 

 tops had been left lying in definite rows, 

 instead of being spread equally over the 

 surface of the ground as they should be. 

 Where such spreading has been neglected 

 one will find that the crop is very patchy in 

 growth, being strong and vigorous along the 

 lines which represent row^s of tops, but com- 

 paratively feeble in the intervals. Crop 

 residues can seldom be utilized as food by a 

 crop of the same species, for the simple reason 

 that many crops refuse to grow in successive 

 years, or even at short intervals, on the same 

 ground. This applies more or less to red 

 clover, turnips, swedes, and beans, though 

 it does not apply to cereals, grass, or man- 

 golds. We have a similar, though not 

 exactly the same, state of things in the case 



