96 THE ROTHAMSTED EXPERIMENTS. 



been the greater at the later date. It is also of interest to 

 observe that the amounts determined in the potash-exhausted 

 soil by the 1-per-cent citric acid solution were about from 

 three to five times as much as the crops would annually take 

 up, which is a fairly consistent relation. 



Further, with reference to these barley-soil results, as 

 superphosphate was applied to both plots, the comparison of 

 the amounts taken up on the two is of less interest than in 

 the case of the potash; but comparison with the results 

 obtained on another plot, otherwise similarly manured, but 

 without superphosphate, shows, as already referred to, that 

 the estimated accumulation of phosphoric acid was approxi- 

 mately indicated by the amount taken up by hydrochloric 

 acid. The results relating to the two plots are, however, of 

 special interest as illustrating, in the one case actual exhaus- 

 Accumuia- tion, and in the other actual accumulation of potash, there 

 potash heing in the one a loss over the forty years of about 1018 lb. 

 shown by of the potash of the soil, and in the other a gain from supply 

 sm-anaiy. f a b out ^ISO lb. ; whilst of the latter amount the results 

 show that hydrochloric acid extracted nearly two-thirds, and 

 citric acid less than one-fourth. It is further of interest to 

 note that Dr Bernard Dyer's results,' obtained on the 1882 

 Potash and samples from the two plots, in each case to the depth of three 

 v1 cid > k^v C ^ mes 9 inches, agree with those formerly obtained by Her- 

 to the sur- mann von Liebig on the wheat-field soils, in showing that 

 face. little if any of either the potash or phosphoric acid artificially 



supplied had gone below the first 9 inches of depth. 

 Analysis of Dr Dyer is also working on the soils of some of the plots 

 wheat-soil. f ^he experimental wheat-field, and these will afford some 

 striking illustrations in regard to the condition of availability 

 of accumulated residue of potash-supply over a long series of 

 years. Thus there is a series of plots which have received 

 the same amount of ammonium - salts and superphosphate 

 each year for forty years, to 1891 inclusive ; one of which has 

 received no potash either during those forty years, or during 

 the eight preceding years ; two received potash during the 

 first eight years, but none since ; and one, besides receiving 

 potash during the first eight years, has received it each year 

 since. The complete manure and crop history of each of the 

 four plots is, so far as potash and phosphoric acid are con- 

 cerned, available for each of the four ten-yearly periods of 

 the forty years — as in the case of plots 2a and 4a in the 

 barley-field. The amount and composition of the crops show 

 great reduction in produce and exhaustion of potash, where 

 none had been applied from the beginning; less reduction, 

 and less exhaustion, where there was a residue of potash from 

 the applications during the first eight years ; and lastly, main- 



