THE ROTHAMSTED EXPERIMENTS 403 



basis, the crop of 1907 required for the roots alone, 180 pounds 

 more potassium than was supplied in the manure and rape cake; 

 and it seems remarkable that the 141 pounds of sodium on plot 

 Ni produced almost as great an effect as the 210 pounds of 

 potassium on plot AC 2. 



It is of interest to note that the total supply of potassium con- 

 tained in the surface soil (6| inches deep) of the peat lands of New 

 York or Illinois, for example, would be sufficient for less than 10 

 such crops as were grown on plots Ni, N2, A2, AC2, AC4, and C2, 

 of Barn field, Rothamsted, in 1907; and that even the total potas- 

 sium in 2 million pounds of the most common type of soil in the 

 Illinois wheat belt (gray silt loam prairie, lower Illinoisan glacia- 

 tion) would be sufficient for only 75 such crops, although it would 

 be sufficient for 50 bushels of wheat per acre every year for 19 

 centuries, if the straw is returned to the land. 



ABANDONED LANDS AT ROTHAMSTED 



Since 1882, a piece of Broadbalk field, which had been cropped 

 with wheat every year since 1844, has been abandoned to nature, 

 except that trees and shrubs have been kept out. Likewise, a 

 piece of Geescroft field, which had been used for beans from 1847 

 to 1881 (only four crops grown during the last n years), and for 

 clover from 1882 to 1885, has been abandoned to volunteer vege- 

 tation since 1885. 



Nothing has been harvested from these pieces of land, not even 

 by pasturing, since they have been left to " lie out," or " run wild." 



The most marked difference that has developed between the 

 herbage of the two fields is the absence of legumes on Geescroft 

 and the abundance of legume plants on Broadbalk, although 

 Broadbalk was abandoned with a wheat crop standing on it (of 

 which some volunteer plants continued to appear for three or four 

 years), while Geescroft was in clover when abandoned. Observers 

 (including Sir John Lawes *) commonly attributed the absence of 



1 In 1900, when I had the deeply appreciated privilege of being shown over the 

 Rothamsted fields by Sir John Lawes (about a month before his sudden death), 

 he climbed the fence like a boy, to take me into Geescroft field and point out a few 

 legume plants (of a single species) the development of which he had been watching 

 for two or three years. C. G. H. 



