THE ROTHAMSTED EXPERIMENTS 



409 



being placed on the line), and Director Hall states that the influ- 

 ence of the fertilizers can scarcely be detected six inches over the 

 line, either in the yield or in the character of the herbage, despite 

 the exceedingly marked differences that have developed between 

 the plots. 



THE CHEMISTRY OF ROTHAMSTED FIELD EXPERIMENTS 



While much chemical work has been carried on from the begin- 

 ning by the Rothamsted Experiment Station in connection with 

 the field experimentation, it has been directed more largely to 

 investigations concerning the composition of the crops produced 

 than to soil analyses. From most of the fields few soil analyses 

 have been reported; but in the case of Broadbalk field some very 

 complete and thorough investigations have been made of several 

 plots. The results are briefly summarized in Table 73. 



The soil samples upon whose analysis the data in Table 73 are 

 chiefly based were collected in 1893, fifty years from the beginning 

 of definite plot experiments on Broadbalk field, although on several 

 plots the final systems of treatment were not fully settled until 

 1852. For this reason the average yields are given for the forty- 

 two years, 1852 to 1893, but tne plant food removed and applied 

 is computed for the fifty years; and, in the main, estimation of 

 plant food removed is based upon the analysis of the actual crops 

 harvested. 



In computing from percentages found by analysis to pounds 

 per acre, Doctor Dyer has used as the weight of fine dry soil per 

 acre 2,590,000 pounds for the first 9 inches, 2,670,000 pounds for 

 the second, and 2,790,000 pounds for the third 9 inches. The cor- 

 responding weights, including stones, are 3,120,000, 3,040,000, and 

 3,000,000 in round numbers. (For the common silt loam soils of 

 Illinois, we have found 300,000 pounds per acre-inch to be practi- 

 cally correct. This would correspond to 2,700,000 pounds per acre 

 for a 9-inch stratum, or 2 million pounds for a 6|-inch stratum.) 



In considering the composition of the soils represented in Table 

 73, it should be kept in mind that the nitrogen reported is total, 

 while the phosphorus and potassium are the portions soluble in 

 strong acid. In the case of phosphorus, this usually represents 



