202 



SCIENCE PROGRESS. 



which is occasioned by a difference in the solubility of the 

 phosphates in the soil, we will take the results relating to 

 plots i A and 2 A. 



PHOSPHORIC ACID IN ROTHAMSTED BARLEY SOILS, 1889, 

 IN POUNDS PER ACRE IN FIRST NINE INCHES. 



These two plots have grown barley continuously for 

 thirty-eight years, and during the whole of this time both 

 have received every year the same quantity of ammonium 

 salts. Plot 2 A has also received every year three and a 

 half cwts. of superphosphate per acre ; while during the 

 whole time no phosphates have been applied to i A. 



On plot 1 A, where the barley has been grown for so 

 many years without any supply of phosphates, the want of 

 phosphates is keenly felt, the average produce being about 

 thirteen bushels less than where phosphates are supplied. 

 It appears by the figures in the above table that plot i A 

 still contains 2452 lbs. of phosphoric acid in the first nine 

 inches of soil (0*097 per cent, of the dry soil) ; and yet it is 

 evident, by comparison with the results on 2 A, that the 

 addition of sixty-four lbs. of phosphoric acid (three and 

 a half cwts. of superphosphate) as manure would greatly 

 increase the produce. The reason of the small availability 

 of the phosphates in this soil is revealed when we look at 

 the amount dissolved by dilute citric acid : out of the 2452 

 lbs. only 152 lbs. are soluble in this reagent. 



On plot 2 A, it appears from the figures in the table 

 that a large accumulation of phosphoric acid remains from 

 the thirty -eight annual dressings of superphosphate which 

 have been applied ; and, further, that more than half of this 

 accumulated phosphoric acid, or 1073 lbs., still remains in a 



