THE ROTHAMSTED EXPERIMENTS 407 



"On the other hand, it is clear that the soil in the garden, which at the com- 

 mencement contained in its upper layers about four times as much nitrogen as 

 the arable land, and would doubtless be correspondingly rich in other constitu- 

 ents, has supplied the conditions under which clover can be grown year after 

 year on the same land for many years in succession. 



"The results obtained on the soil in the garden seem to show that what is 

 called 'clover sickness,' cannot be due to the injurious influence of excreted 

 matters upon the immediately succeeding crop. 



"That clover frequently fails coincidently with injury from parasitic plants 

 or insects cannot be disputed; but it may be doubted whether such injury 

 should be reckoned as the cause, or merely the concomitant, and an aggravation, 

 of the failing condition." 



"When land is not what is called 'clover-sick,' the crop of clover may fre- 

 quently be increased by top dressings of manure containing potash and super- 

 phosphate of lime ; but the high price of salts of potash, and the uncertainty of 

 the action of manures upon the crop, render the application of artificial manures 

 (as top dressings) for clover a practice of doubtful economy. 



"When the land is what is called 'clover-sick,' none of the ordinary manures, 

 whether ' artificial ' or natural, can be relied upon to secure a crop. 



"So far as our present knowledge goes, the only means of securing a good 

 crop of red clover is to allow some years to elapse before repeating the crop 

 upon the same land." 



In his book on the "Rothamsted Experiments" (page 146), 

 Director Hall gives the complete data and the following summary 

 of the clover grown year after year on a small plot of rich garden 

 soil at Rothamsted: 



RED CLOVER ON RICH GARDEN SOIL, ROTHAMSTED 

 Pounds per Acre 



During the fifty years there have been only two crop failures 

 (1895 an d 1900); but the plot required seeding only five times 

 during the first twenty years (1854, 1860, 1865, 1868, and 1871), 

 whereas since 1874 it has been seeded or reseeded almost every 

 year, and sometimes two or three seedings in one year have been 

 required to secure a stand. Late yields of dry matter are: 2887 



