EESIDUES LEFT BY LEGUMINOUS CROPS 203 



which have been completed, showing a comparison of the roots 

 and the barley after fallow and after clover (or beans) re- . 

 spectively i.e., of the crops coming in the second and third 

 years after the growth of the leguminous crop. 



The results show that where the manuring is with minerals 

 only the effect of the leguminous crop is very marked both in 

 the roots and in the barley, i.e., that the nitrogen introduced by 

 the growth of clover is operative, not only in the wheat which 

 follows it, but also in the roots and the barley which follow the 

 wheat ; in fact, in all the crops of the rotation until the clover 

 comes round again. The root crop is increased by 25 per cent., 

 and the barley crop by about 37 per cent., the magnitude of 

 the increase being due to the fact that the leguminous crop 

 represents the only source of nitrogen on this plot. When, 

 however, the manure put on to the Swedes contains nitrogen, the 

 effect of the nitrogen stored up in the soil by the clover crop 

 two seasons before is masked by the fresh nitrogen introduced, 

 and produces no increase of crop. It, however, becomes 

 manifest in the succeeding barley crop, which is 23 per cent, 

 greater on the portion cropped with leguminous plants than on 

 the fallowed portion, so that we can say the value of a clover 

 crop is felt for three years after its growth in all the crops of 

 the rotation, even under the ordinary conditions of farming when 

 a manure introducing large quantities of nitrogen is used once 

 during the rotation. Of course it must be remembered that the 

 above mean results are for the six last courses after ten 

 rotations had been completed, and that as the benefit is 

 doubtless somewhat cumulative from one rotation to the 

 next, the results represent not so much the value of a single 

 clover crop as of its constant introduction into the rotation 

 instead of taking a bare fallow. On the other hand, if we 

 compare the effects of the single crops, we find that the crops 

 of beans, just as they show little effect in the succeeding wheat 

 crops, so also they cause but a small benefit to the roots and 

 barley coming later still. The continuous enrichment of the 

 land shown in the above table has therefore been due in the 



