fifty bushels, with an average for the thirteen years of 39^ bushels. 

 The first three years during which no manure was applied, the average 

 yield was only 21^4 bushels, a decrease of nearly one-half, followed in 

 the succeeding periods of four years each by average yields of 17^, 12, 

 9^5, and 13^ bushels; against, for the corresponding periods on plot 3, 

 continuously without manure, 8^4, 13^, 10^, and 12^ bushels. Or, 

 taking the average of the nineteen years of yield without manure on plot 

 1 6, we have 14^5 bushels, against, over the same years, 13^ bushels, 

 on plot 5, with mineral manures only, since 1852, and nfo bushels on 

 plot 3, unmanured since 1839. It is fair to presume, moreover, that 

 some of the greater yield of plot 16, from 1864-1883, over that of plot 

 3. is due to the residue of the mixed mineral manure, which, as will be 

 seen further on, has some effect on succeeding crops. 



If, as the above results have demonstrated, there is practically no 

 residue from previous application of ammonium-salts, the question arises, 

 What becomes of the nitrogen of the manure not taken up by the crop ? 

 This point is illustrated by the results given in Table V. The plots 

 there tabulated all received the same amount of nitrogen in manure, with 

 differing mineral manures, and they are given in the order of their aver- 

 age annual increased yield of nitrogen in the crops over plot 5, with 

 mineral manure alone. The first column shows the estimated average 

 annual increased yield of nitrogen per acre in the crops ; the second, the 

 estimated annual loss of nitrogen as nitric acid by drainage ; the third, 

 the estimated annual excess of nitrogen in the surface-soil over that on 

 plot 5 with the mineral manure alone; and the last column shows the 

 relation which that excess in the soil bears to 100 increased yield of 

 nitrogen in the crops. 



The plots were manured as follows: 



Plot 10 Amm. -salts = 86 Ibs. N. 



" ii Amm. -salts _ 86 Ibs. N., and superphosphate. 



" 12 Amm. -salts 86 Ibs. N., superphosphate and soda. 



" 13 Amm.-salts = 86 Ibs. N., superphosphate and potash. 



" 14 Amm. -salts = 86 Ibs. N., superphosphate and magnesia. 



" 7 Amm.-salts = 86 Ibs. N., and mixed mineral manure. 



" 9 Nitrate of soda = 86 Ibs. N., and mixed mineral manure. 



TABLE V. 



BROADBALK EXPERIMENTAL WHEAT-FIELD. 



Estimated Nitrogen per acre per annum. 



