114 EXPERIMENTS UPON ROOT-CROPS 



the roots alone than was supplied in the form of manure. 

 Table XLII. shows the nitrogen supplied and removed from 

 Plots 4, where there was a full supply of mineral manures, and 

 from Plots 1, where dung was used with nitrogenous manures. 



The results show that both the nitrate of soda and the rape 

 cake are very effective manures, about three-quarters of the 

 nitrogen they supply each year being recovered in the roots 

 removed from the land ; the ammonium-salts, and ammonium- 

 salts mixed with rape cake are less effective, the recovery being 

 between 50 and 60 per cent, of that applied. On the plots 

 receiving dung, the proportion of nitrogen recovered at once 

 becomes very much less, sinking to about one-third of that 

 supplied in the manure. It is known that there is a very large 

 accumulation of nitrogen in the soil of these continuously 

 dunged plots, though not sufficient to make up all the difference 

 between the nitrogen supplied and that removed in the crop. 

 Of the nitrogen unaccounted for, some has been washed as 

 nitrate into the subsoil, and some liberated as nitrogen gas by 

 the agency of bacterial changes. 



Thus, when dung and nitrate are used, 115*8 lb. of nitrogen 

 is recovered in the crop as compared with 63*3 lb. recovered 

 from the dung when used alone ; if we deduct the 63*3 lb., as 

 due to the dung, from the 115"8 lb. we obtain 52 '5 lb., which 

 may be taken as the return from the nitrogen of the nitrate of 

 soda when it is used in conjunction with dung. This amounts 

 to 61 per cent, of the 86 lb. of nitrogen supplied, a proportion 

 which compares favourably with the proportion recovered from 

 nitrate of soda when used with a mineral manure only, if we 

 take into consideration the fact that a much bigger crop is being 

 grown with the two manures in conjunction than with either 

 singly ; and, as we have seen before, it is the smaller applications 

 of manure which give the best proportionate returns. 



These results, showing the large proportion of the nitrogen 

 of nitrate of soda and other nitrogenous manures that is 

 recovered, even when they are used in large amounts with 

 dung year after year on the same land, lend no colour to the 



