18 RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



crops grown without any supply of it was much more than in either of 

 the Cereals, the Eoot-crops, or Potatoes, grown under similar conditions. 



Thus, as the bottom line of the upper division shows, there was an 

 average, over the 32 years, of 24-8 Ibs. of nitrogen, per acre per 

 annum, in the crops without any manure, but of 35 -4 Ibs. with the 

 mineral manure without nitrogen ; whilst the amount was raised to 

 only 4 2 '4 Ibs. by the addition of nitrogenous manure. Over the first 8 

 years, however, the yield was very much higher, being for the three 

 plots, respectively, 48*4, 60'2, and 69'0 Ibs. Over the second period of 

 8 years the average was not far from that of the whole 32 years ; but 

 over the third and fourth periods it was much less. 



As in the case of the total produce itself, so also in that of the 

 nitrogen in the total produce, if we take the averages of the years of 

 crop only, as given in the bottom division of the Table, we have a 

 much higher average yield per annum over the 4 years of crop of the 

 last 8 years, than over the years of crop of either the second or the 

 third period of 8 years. Indeed, on the two manured plots, there is an 

 average annual yield of nitrogen per acre, over the 4 years of crop 

 during the last 8 years, not far short of the average of the first 8 years. 

 Thus, with the purely mineral manure, there is an average annual 

 yield of nitrogen over the first 8 years of 60*2 Ibs., and over the 4 

 years of crop of the last 8 years, of 53*3 Ibs. ; and with the mineral 

 and nitrogenous manure together, over the first 8 years, of 69 '0 Ibs., 

 and over the 4 years of crop of the last 8 years, of 57 '4 Ibs. 



That is, with the intervention of Fallow, we have, though not 

 good agricultural crops, yet really large yields of nitrogen, compared 

 with those obtained in many of the preceding years ; and very large 

 yields without any supply by manure, compared with those obtained 

 under the same conditions with any of the ft0ft-Leguminous crops. It 

 would appear probable, therefore, that if a suitable mechanical condition 

 of the land could have been maintained, fair crops, and large yields of 

 nitrogen, would also have been maintained. 



Upon the whole, then, although the crop practically failed, when it 

 was attempted to grow it year after year on the same land, it never- 

 theless accumulated, in its above-ground produce, much more nitrogen 

 over a given area than the crops of the other families, but was little 

 benefited by an artificial supply of nitrogen. 



I have now to record a still greater failure, with another crop of 

 the Leguminous family namely, Trifolium pratense, or Red Clover. 

 The results are summarised in Table VIII. (p. 19). 



The Table is headed Red Clover sown frequently on the same land ; 

 and the first column shows that the period of experiment was 29 years, 

 from 1849 to 1877 inclusive. But the details show that, although 

 Clover was sown 15 times, in only 7 of the 29 years was any Clover- 

 crop obtained ; whilst about one-fifth of the produce of the whole series of 

 years was yielded in the first year, 1849. It is, indeed, well known in 

 agriculture, that Clover will not grow, under ordinary conditions, more 



