THE ROTHAMSTED EXPERIMENTS 391 



of soil fertility, if the soil became exhausted for potatoes, it should grow any 

 other crop, because the usual analysis shows the same constituents present in all 

 of our plants, not in the same proportion, but all are present and all necessary, 

 so far as we know. This field was planted in barley, and on this experimental 

 plot that had ceased to grow potatoes they got 75 bushels of barley." l 



While the avoidance of possible injury to plants from the pos- 

 sible toxic substances that may possibly be excreted from the roots 

 of the same kind of plants is by no means precluded from among 

 the possible benefits of crop rotation, the Rothamsted data fur- 

 nish little evidence in favor of such a theory, and even less in sup- 

 port of the Whitney theory, that crop rotation alone will maintain 

 the fertility of the soil. On the other hand, the residual effect of 

 the farm manure applied to plot 3 (Table 69), previous to 1882, 

 is still apparent after the removal of twenty-five crops, in com- 

 parison with the unfertilized land. 



Clover was seeded in 1905 on plots 6, 8, and 10, and cowpeas on 

 plots 5, 7, and 9. The cowpeas failed, and in 1906 clover was seeded 

 on 5, 7, and 9. The clover yields thus far reported are recorded 

 in Table 69. They are of some interest for comparison with the 

 1906 clover on Agdell field (Table 56), where clover " sickness " has 

 been recognized by the Rothamsted Station as the probable cause 

 of frequent failure during more than half a century. There is much 

 evidence to show that soils frequently become " sick " from the 

 continuous growing of flax and of certain legume crops. " Clover 

 sick " land and " bean sick " land are expressions common to 

 nearly all countries. Cowpea wilt and flax wilt are well understood 

 fungous diseases, and the evidence thus far secured indicates that 

 clover " sickness " is also due to a fungus rather than to any pos- 

 sible toxic excreta. (See below.) 



HAY EVERY YEAR FROM PERMANENT MEADOW AT ROTHAMSTED 



In 1856, experiments were begun at Rothamsted in top-dressing 

 meadow land with various fertilizing materials, as indicated in 



1 From page 14 of Farmers' Bulletin 257, U. S. Department of Agriculture. 

 The careful student is advised to secure a copy of this interesting bulletin and 

 also Bulletins 22 and 55 of the U. S. Bureau of Soils in which are set forth in greater 

 detail the unique theories of Whitney and Cameron concerning soil fertility. They 

 should be read in connection with Circulars 72, 105, 123, 124, and 129, of the Uni- 

 versity of Illinois Agricultural Experiment Station. 



