528 On the Growth of Barley by different Manures, S^'c. 



would require the record and coincident study of the percentages 

 of ash in that dry matter — of which unfortunately our series of 

 determinations are at present too incomplete. 



We pass on, therefore, after these few observations on the 

 effects of season and manuring upon the percentage of nitrogen 

 in the barley crop, to the application of the analytical results to 

 determine the proportion of nitrogen recovered in the increase of 

 crop, for a given amount supplied in manure. Table XVllI. 

 supplies us with our data on this point. 



A preliminary point of interest in this Table is, the informa- 

 tion it affords of the amount of nitrogen annually taken from 

 the land in the produce, where none was supplied in manure. 

 The highest amount of nitrogen thus stored up from the unaided 

 soil and season resources was in 1854, namely, 32i lbs. per 

 acre ; the lowest amount was 17^ lbs. in 1856 ; and the average 

 annual yield, taking the mean of the 6 years, was about 28^ lbs. 

 It may be mentioned, that this latter amount, is more than that 

 annually deposited in rain and other aqueous depositions, in the 

 forms of ammonia and nitric acid. Investigation, of which there 

 is at the })resent time nuich going <m in reference to this subject, 

 has still to determine the source or sources of this annual excess 

 of assimilated nitrogen, beyond that supplied in the combined form 

 in the measured and analysed aqueous depositions. Whether it be 

 due to exhaustion of previously accumulated nitrogen in the soil — 

 to direct condensation by the latter of the nitrogenous compounds 

 occurring in the atmosphere — to the formation of ammonia or 

 nitric acid within the soil at the moment of the evolution by 

 chemical changes of certain elements in the nascent state — to the 

 accumulation of combined nitrogen from the atmosphere by the 

 plant itself — or to its assimilation of the free nitrogen of the 

 atmosphere — whether, or In wliat proportion, these several possible 

 sources may take part in the result, is as yet a great problem 

 open for solution? 



For the convenience of round numbers, and to be sure of 

 making full allowance for impurity in the manures employed, we 

 have, as already stated more than once, assumed that the 200 lbs. 

 of ammoniacal salts per acre (100 lbs. each sulphate and muriate), 

 and the 275 lbs. nitrate of soda, respectively supplied 41 lbs. of 

 nitrogen, equal 50 lbs. of ammonia, per acre. The double amounts, 

 namely, the 400 lbs. of mixed ammoniacal salts, and the 550 lbs. 

 nitrate of soda, of course each supplied, on tlie same calculation, 

 82 lbs. of nitrogen per acre, equal 100 lbs. of ammonia. Tlie 

 2000 lbs. of rape-cake, on the lowest estimate, would supply 

 82 lbs. also, but more probably nearer 100 lbs. nitrogen per acre. 

 Taking, as we have done, low rather than high estimates of the 

 nitrogen supplied in the various manures, it is obvious that the 



