128 PLANT LIFE ON THE FARM. 



pared with that of wheat grown continuously on the same 

 soil, without the intervention of fallow, and equally .without 

 manure. Under such circumstances, the average pro- 

 duce for 25 years after fallow has heen 18 hushels per 

 acre, as contrasted with an average of 12 hushels where 

 the wheat has been grown continuously. The weight per 

 bushel was the same in both cases. The average quantity 

 of straw after fallow was 1,786 Ibs., as contrasted with 

 1,221 Ibs. where the crop was grown continuously. 



Rotation. The practice of rotation of crops is amply 

 borne out by what occurs in nature and by chemical experi- 

 ments, although not in the manner that might at first 

 have been supposed. Leguminous plants, such as clover, 

 beans, vetches, though containing so much nitrogen 

 in -their composition, are not only not specially benefited by 

 nitrogenous manures, but they absolutely leave the land 

 richer in nitrogen than it was before (Lawes and Gilbert), 

 and thus prepare it for the growth of corn crops, which, 

 though chiefly starch-producing, are yet specially bene- 

 fited by nitrogenous manures. 



In growing beans and wheat alternately at Kothamsted, 

 it was found that eight crops of wheat grown alternately 

 with beans supplied nearly as much produce (corn), and 

 nearly as much nitrogen in that produce as were furnished 

 by sixteen crops of wheat grown without manure. Here, 

 then, the manure supplied to the beans not only favoured 

 those plants, but left a residue in an available form for the 

 wheat. 



Botanically, the good effects of rotation are dependent on 

 the variations in the mode of growth and in the internal 

 structure of roots, which allow of different layers of soil 



