206 



CKOPS GROWN IN ROTATION 



growing a crop of roots, a residue which increases the barley 

 crop by 41 per cent. ; even two years later, after an inter- 

 vening bare fallow, sufficient still remains to increase the 

 wheat crop by 8*3 per cent. A similar increase in the 

 barley of about 41 per cent, is brought about by the residues 

 of the nitrogenous manuring applied to the Swede crop on 

 the plots which, instead of being fallowed, carry clover or 

 beans as the third crop in the rotation. On the leguminous 

 crop itself, however, the residues of nitrogen still in the soil have 

 a depressing effect, the average production of beans or clover 

 being 18 per cent, less on the plots which receive nitrogen 

 for the Swede crop than on the corresponding plots getting 

 no nitrogen, a result of nitrogenous manuring which has been 

 noted before. 



Further evidence of the duration of manurial residues is to 

 be obtained by comparing the plots from which the roots were 

 removed with those to which the roots were returned, and noting 

 the effects on the succeeding crops of the rotation. For this 

 purpose it will be wise to consider only the plots on which the 

 Swedes receive nitrogen as well as the minerals, for on them 

 only is there a crop of Swedes big enough to leave any per- 

 ceptible residue. Table LXXI. shows the average results 



TABLE LXXI. Effect of Carting and of Feeding Roots on the Yield 

 of succeeding Crops. No Clover grown. 



(grain and straw) for five courses on the fed and carted 

 portions, where a bare fallow is taken in each course. 



Taking the figures in the last column, we see that the effect 

 of the root crop on the succeeding barley is considerable, for 



