206 



CROPS 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 intervening 

 bare fallow, sufficient still remains to increase the Avheat crop 

 by nearly 7 per cent. A very similar increase in the barley 

 crop, of 39 per cent, instead of 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 crojo 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 l^eans or clover 

 being 11 '6 per cent, less on the plots which receive nitrogen 

 for the SAvede crop than on the corresponding plots getting 

 no nitrogen, a result of nitrogenous manuring which has been 

 noted before. 



Fmther evidence of the duration of manurial residues is to 

 be obtained by comparing the plots from which the roots are 

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

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

 pmpose 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 l^ig enough to leave any per- 

 ceptible residue. Table LXXI. shows tlie average results 



Table l.XXr. 



(grain and straw) for tlie last 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 



