196 CKOPS GEOWN IN ROTATION 



It should be remembered that each of these three plots is 

 fm'ther subdivided into four quarter plots, in the first place the 

 third crop may be clover or a bare fallow, and again the 

 roots are carted off or fed on the land. 



The effect of the mineral manures without nitrogen is very 

 marked on the roots; during the last five com-ses the crop 

 averaged 208 cwt. per acre, as against 16 cwt. per acre only 

 on the unmanured plot. Even on the most impoverished of 

 the quarter plots, that from which the roots are always carted 

 and where a bare fallow is taken after the barley, the produc- 

 tion amounted to 178 cwt. (see Table LXIV.), although the 

 plot had been receiving no nitrogen for thirty-six years 

 previously, nor had any residues of the previous crops, which 

 would contain nitrogen, been returned to the ground. Where 

 the roots had been put back and where also a leguminous 

 crop was taken in the rotation, the crop amounted to 245 cwt., 

 the increase being due to the extra nitrogen thus returned 

 to the soil. These results illustrate the great dependence 

 of the Swede crop upon a plentiful supply of mineral, and 

 especially of phosphatic, manures ; the latter in particular 

 seem to stimulate the development of ii1:>rous roots, thus 

 enabling the plant to utiHse the resources of the soil. Again, 

 the cultivation to which the land is subjected for the Swede 

 crop is calculated to nitrify reserves of nitrogenous material in 

 the soil and render the plant more or less independent of a 

 direct supj^ly of nitrogen. Thus, in ordinary farming practice 

 with the land in good condition the Swede crop only requires 

 a small nitrogenous dressing, but should always have a 

 comparatively large amount of phosphoric acid, in order to 

 enable it to make the most of the reserves in the soil and of 

 the dung which is generally used with this crop. 



The effect of the mineral dressing is much less marked on 

 the barley than on the roots, it only increases the average 

 crop from 15-8 to 20 bushels per acre. This increase again 

 is wholly found on the plots growing clover and beans 

 and so receiving nitrogen collected from the air; the two 



