148 EXPERIMENTS UPON LEGUMINOUS CROPS 



average over the period of fifty years is 140 lb., or about as 

 much as a fair but not large crop grown occasionally under 

 the ordinary conditions of agriculture. 



Analysis of the soil taken at intervals would seem to show 

 a considerable falling- off in the amount of nitrogen and carbon 

 contained in the surface soil, not sufficient however to account 

 for all the nitrogen removed by the clover crop. 



It will be apparent from a consideration of the crops 

 reported for the later years of the experiment that great diffi- 

 culty is beginning to be experienced in maintaining a plant 

 of clover ; re-seeding, which was only necessary five times in the 

 first twenty years, had to be carried out eight times from 

 1904-13, during which time the crop wholly failed for one year. 

 During January 1897 the plots were inoculated with the 

 watery extract of the rich kitchen-garden soil at Rothamsted. 

 This did not however arrest the failure which was in progress 

 at that time. Again, in March 1897 and in July 1899, all the 

 plants were removed by hand, burnt, and their ashes returned, 

 and the surface soil was carefully picked over by hand, to 

 remove the Sclerotia of the fungus Sclerotinia trifoliorum, many 

 of which were found. The soil was also dressed with carbon 

 bisulphide as a fungicide, before fresh seed was sown. In 1903, 

 which was a favourable year for the growth of clover, a fair 

 plant was obtained by re-seeding, and in the spring of 1904 the 

 best crop for many years was cut from this plot. Notwith- 

 standing the repeated failures to grow clover continuously on 

 ordinary arable soil and the increasing difficulty of maintaining 

 a plant on the rich garden soil, which is the one place where any 

 growth has been continuous, it is noteworthy that when clover 

 grows in a mixed herbage on grass-land it increases in amount 

 from year to year under suitable conditions of manuring. It has 

 already been pointed out that on the grass plots in the park, 

 where mineral manures including potash are applied every year, 

 as on Plots 15, 6 and 7, the proportion of leguminous plants, 

 including red clover, increases from year to year, without there 

 being any sign of " clover sickness " setting in. Nor can this 



