530 On the Groicth of Barlei/ hj different Manures, Sfc. 



nitrogen — that is, the same as the larger amounts of ammoniacal 

 salts and nitrate of soda — it will then have returned rather the 

 largest proportion of any, namely, 43'6 per cent. Assuming, 

 however, that the 2000 lbs. of rape-cake supplied its maximum 

 amount, or 100 lbs. of nitrogen per acre, then the return would 

 be only 35-8 per cent, of the supplied nitrogen. The probability 

 is, that the average amount supplied was very nearly the mean 

 between the two ; and, in that case, the proportion of nitrogen 

 returned in increase, for that supplied by rape-cake, will agree 

 very closely with that obtained when the ammoniacal salts and 

 the larger amount of nitrate of soda were employed.* 



The fact is, then, that in each case the average percentage of 

 the supplied nitrogen, which was recovered in the increase, was 

 rather greater where the excessive amounts of nitrogen were sup- 

 plied in manure, which gave over-luxuriant and damaged crops, 

 and a less amount of increased produce for nitrogen supplied. 

 This result, of the larger proportion of supplied nitrogen re- 

 covered, where the amounts in manure were excessive, is obvi- 

 ously due to the much higher percentage of nitrogen in the 

 produce, under these circumstances. It has been seen, that an 

 increased percentage of nitrogen by the use of it in manure is, if 

 beyond a comparatively narrow limit, most probably accom- 

 panied with a depreciation in those qualities which in practice 

 give high rate of value to the corn. This applies more particu- 

 larly where the demand is chiefly for malting purposes. Upon 

 the whole then, the slightly larger proportional return of nitrogen 

 in increase for nitrogen supplied in manure, where the larger 

 amounts of the latter were employed, is but a very questionable 

 advantage. 



The general result is seen to be that, in the experiments in 

 question, when the nitrogen supplied in manure was not exces- 

 sive, scarcely 40 per cent, of it was recovered in the increased 

 produce of corn and straw obtained, taking the average of several 

 successive years. In some of the individual years there were less 

 than 30 per cent, of the supplied nitrogen recovered, and in others 



. that is, where the tendency to corn was the highest — there were 



nearer, or even over 50 per cent, recovered. 



In thus speaking of the proportion of the supplied nitrogen 

 recovered in the immediate increase of the barley crop, our form 

 of statement must be understood as only representing the practical 

 result as measured by the difference between the amount of 

 nitro"-en in the produce with nitrogenous manures, and in that 

 without them. It must be admitted, that we have not the means of 



* It should be mentioned that the above results relating to the large amounts 

 of ammoniacal salts are founded, for three years out of the six, upon single deter- 

 minations of nitrogen in the produce, instead of duplicates ; and those relating to 

 the rape-cake apply to only three years instead of six. 



