of manures. The usual plan of deducting the produce of a 

 similar piece of land, to which the manure under examination 

 has not been applied, is generally the only course open to us. 

 This method, however, leads not unfrequently to serious error 

 when we take the produce of a continuously unmanured plot 

 as the basis for our calculation. The produce of such a 

 plot is certain to diminish seriously as time goes on, and 

 if we deduct the produce of this exhausted land from the 

 produce obtained by manuring, we are virtually putting to 

 the credit of the manure the fertility lost on the unmanured 

 plot. 1 Bearing these considerations in mind, we take the 

 mean produce of the two plots on which the roots were fed 

 or ploughed in, in the superphosphate division of the field, as 

 representing most nearly the original productiveness of the 

 land without nitrogenous manure. Subtracting the mean 

 produce of these plots from the mean produce of the two 

 corresponding plots in the division receiving nitrogenous 

 manure, we find, as the result of that manuring, the pro- 

 duction of 7 tons of roots consumed by sheep, and the 

 subsequent production of 10 bushels of barley and \ bushel 

 of wheat, with, on the bean and clover plot, 845 Ibs. of mixed 

 clover hay, and bean crop. If we take the four clover crops 

 only, which, however, fell in the later years of the experiment, 

 1874, 1882, 1886, 1894, we have an average produce on the 

 superphosphate plot of 2 tons 18 cwts., and on the plot having 

 nitrogenous manure of 3 tons 7 cwts. of hay ; the mean excess 

 of clover-hay on the plot receiving nitrogenous manure was 

 thus 9 cwts. In the seven bean crops, the mean produce on 

 the superphosphate plot was 16|- bushels, and on the plot 

 receiving nitrogenous manure 23f bushels ; there was a 

 difference therefore in favour of the latter of 7 bushels. 



We have here the result of the most exhaustive trial which 

 has yet been made of the influence of nitrogenous manure 

 in a rotation. From our present point of view we may con- 

 sider the manure to have been applied to the turnips by the 

 outgoing tenant ; he feeds the roots on the land, and claims 



1 The only truly accurate method of ascertaining the comparative value of 

 different manures is to experiment at the same time with various quantities 

 of each. Those quantities of manure which yield the same amount of produce 

 are clearly those which have an equivalent value. 



