72 



THE ROTHAMSTED EXPERIMENTS. 



Nitrogen 

 supplied in 

 the dung. 



Nitrogen 

 stored in 

 the soil. 



stopped 

 after 

 twenty 

 years. 



Increase 

 over no- 

 manure 



plot. 



than 60 bushels of barley per acre, in fifteen years between 

 50 and 60 bushels, in fifteen between 40 and 50 bushels, in 

 five between 30 and 40 bushels, and in only one year below 30 

 bushels. The average yield was, over the first twenty years 

 48£ bushels, over the second twenty 49 bushels, and over the 

 forty years 48-f bushels, against 16| bushels without manure. 



So much for the produce of barley obtained by the un- 

 usual application of 14 tons of farmyard manure per acre per 

 annum for forty years in succession. It is estimated that 

 the manure supplied about 200 lb. of nitrogen per acre per 

 annum, or over twenty years 4000 lb. of nitrogen. It is further 

 estimated that, at the end of the first twenty years, not more 

 than 14 or 15 per cent of this large amount of nitrogen had 

 been removed in the increase of crop. There must, therefore, 

 have been a great accumulation of nitrogen, and of other con- 

 stituents, within the soil ; and analysis proved that this was 

 the case. Indeed, it was calculated that, if there were no 

 loss of nitrogen, by drainage, by evolution of free nitrogen, or 

 otherwise, and if the accumulated residue were as available 

 as that which had already been effective, the produce should 

 be maintained at the level of that of the first twenty years 

 for nearly 150 years more ! 



Let us see what was the result of stopping the application 

 of manure on half the plot after the first twenty years ? This 

 is shown in the lower half of the table. Comparing the 

 second and third columns, it is seen that there was a tendency 

 to increase in yield where the application of the farmyard 

 manure was continued, and to decrease where it was dis- 

 continued. This result is brought prominently to view in 

 column 4, which shows the reduction in the amount of 

 produce on the manure-residue plot compared with that 

 where the application was continued. 



The averages at the foot of the table show that over the 

 first twenty years, with the continuous application, the yield 

 was 48£ bushels, whilst over the succeeding twenty years 

 it was, where the application was continued 49 bushels, 

 but where it was discontinued only 30|- bushels; showing, 

 therefore, an average annual deficiency under the influence of 

 the residue only, of 18f bushels, or of 38.3 per cent. 



Taking as the standard of comparison the unmanured pro- 

 duce (which, however, itself gradually declined), the last two 

 columns show that over the first twenty years there was an 

 average annual increase of 28£ bushels by the application of 

 the farmyard manure ; and that over the second twenty years 

 there was an average annual increase of 35f bushels where 

 the application was continued, and of only 17 bushels where 

 it was discontinued. 



