182 



THE ROTHAMSTED EXPERIMENTS. 



Sulphate 

 of potash. 



Sulphate of 

 magnesia. 



Sulphate 

 of potash, 

 soda, and 

 magnesia. 



Reduction 

 in produce 

 from, ex- 

 haustion 

 and bad 

 seasons. 



Effect of 

 potash. 



To plot 13, besides the ammonium-salts and superphosphate, 

 sulphate of potash was applied each year of the 40, and it 

 had also received potash previously. The average annual pro- 

 duce was, over the first 20 of the 40 years 33|- bushels, over 

 the second 20, 29f, and over the 40 years 31f bushels. 



On plot 14, besides the ammonium-salts and superphosphate, 

 sulphate of magnesia was applied ; and, as on plots 12 and 

 13, some potash had been applied prior to 1852. The average 

 annual produce was, over the first 20 of the 40 years 33f 

 bushels, over the second 20, 28f bushels, and over the 40 

 years 3 If bushels. 



On plot 7, in addition to the ammonium-salts and super- 

 phosphate, sulphates of potash, soda, and magnesia were 

 applied ; and there was an average annual yield during the 

 first 20 years of 35| bushels per acre, during the second 20 

 of 31 bushels, and during the whole 40 years of 33| bushels. 



It will be observed that in the case of every one of the 

 plots to which Table 51 refers, and which we have just been 

 considering, the produce is less over the second than over the 

 first 20 years of the 40. Eeference to Tables 48 (p. 173) and 

 47 (p. 168) will show that this was also the case with the 

 produce of every other plot in the field. It was so on plot 

 7 with the most complete artificial manure ; and it was so on 

 plot 2 with farmyard manure every year, and great accumu- 

 lation of manure-residue from year to year. It is obvious, 

 therefore, that the decline over the latter half of the 40 years 

 is by no means to be attributed exclusively to exhaustion. 

 Eeference to the details in the body of the tables, and to the 

 summaries at the bottom of them, will show that there were a 

 good many seasons of considerably less than average produce 

 during the second 20 years of the 40, and that there were some 

 very bad ones, especially in the fourth period of 8 years ; so 

 that it is to less favourable seasons that the decline in yield 

 over the latter half of the period must in many cases be 

 largely attributed. Nevertheless, there can be no doubt that 

 exhaustion has had a considerable share in the result in the 

 case of many of the plots. 



Comparing the produce on plots 12, 13, and 14, with that 

 on plot 11 without potash, the effect not only of the direct 

 supply, but of a residue from long previous applications of 

 potash is clearly shown ; but the deficiency with residue only, 

 compared with the produce with annual supply of potash, is 

 very evident during the later periods. 



Both the amount and the limitation of the effect of the 

 residue, compared with the annual supply of potash, are strik- 

 ingly illustrated by the results in Table 52. There are there 

 given the amounts, in lb. per acre, of potash, soda, and phos- 



