viii.] NORFOLK ROTATION. 73 



much of their food from the lower portions of the 

 soil, whereas other plants send out their roots amongst 

 the surface soil, and are shallow rooted. Thus the 

 clover roots strike deeply into the soil, and really 

 enrich the upper soil, by adding to it matter drawn 

 from beneath it. Wheat is found to grow luxuriantly 

 upon land in which the clover has flourished. A good 

 clover ley is a tolerably sure promise for a fine crop 

 of wheat. This probably arises from two causes, 

 which readily explain this well known fact. The 

 clover has not drawn from the upper soil the food 

 which the wheat requires, but has stored up in its 

 closely matted roots, a large quantity of nitrogenous 

 matter on which the wheat plant can feed. The roots 

 of the wheat also find in the clover ley, freedom for 

 their growth, amidst the supplies on which it has to 

 rely for nourishment 



149. Another illustration of the conditions which 

 influence the rotation of crops is shown in the case of 

 beans following wheat; and the table already given 

 (41) shows the substances drawn by each of these 

 crops. Wheat requires a large supply of silicates, 

 beans take one-tenth the quantity; on the other hand, 

 wheat requires one-fourth the potash and one-half the 

 phosphoric acid, that the bean crop needs. So also, 

 amongst the white straw corn crops there is another 

 difference observable, for whilst wheat roots deeply, 

 barley roots shallow ; and these crops therefore draw 

 their supplies from two different layers in the soil. 



150. The Norfolk rotation, or the four years* 

 course of cropping, is a good representative system, 

 and one which has probably been more largely, and 

 more generally adopted than any other. It consisted 

 of the following course of crops : 



1st Year, Turnips or other Root Crop. 

 2nd ,, Barley. 

 3rd ,, Clover. 

 4th Wheat 



