III.] RECOVERY OF NITROGEN IN CROP 99 



From many of the Rothamsted experiments it is 

 possible to calculate how much of the manure applied 

 year after year has been eventually recovered in the 

 crop ; with the mangold crop it will be shown later that 

 (Table LXIII.) 78 per cent, of the nitrogen applied as 

 nitrate of soda was recovered in the crop, the percentage 

 falling to 71 for rape cake, 57 for ammonium salts, and 

 only 31 per cent for dung. When manures were 

 applied to plots which were also enriched with dung the 

 recovery was less in all cases, the usual law of diminish- 

 ing returns coming into play. 



It cannot be said that the conclusions which may be 

 drawn from these results as to the relative availability 

 of different compounds of nitrogen are in any way 

 endorsed by their price in the market, or by the general 

 opinions of farmers. From the experimental point of 

 view the value of the different compounds of nitrogen, 

 unit for unit, ought to be proportional to their avail- 

 ability ; a slow-acting manure not only involves a delay 

 in realising the capital that has been put into the land, 

 but much of the residue is never recovered at all. Not- 

 withstanding this the farmer has a strong preference, to 

 which credit must be given as founded upon experience, 

 for the organic sources of nitrogen ; furthermore, prices 

 fluctuate in accordance with accidents of supply that 

 are quite independent of agriculture. For example, 

 the relative value of nitrogen in nitrate of soda and 

 sulphate of ammonia, which may be regarded as 

 equally valuable in farming opinion, has fluctuated 

 widely of late years ; on occasion the nitrogen in 

 sulphate of ammonia has been the dearer of the two, 

 while at other times it has been so much the cheaper 

 that the price per ton of sulphate of ammonia, with 

 20-21 per cent, of nitrogen, has fallen below that of 

 nitrate of soda with 15-16 per cent, of nitrogen. The 



