494 On the Groioth of Barley hy different Manures, Sfc. 



into the amounts of loarley obtained in some of the same seasons, 

 under very different, but also to a certain extent known conditions 

 of growth, in other fields. By the comparisons that will thus be 

 afforded, Ave shall get some useful check upon the conclusions 

 hitherto arrived at. At the same time, so far as those conclusions 

 are to be trusted upon their own independent evidence, they will, in 

 their turn, serve to afford some insight into the comparative chemi- 

 cal conditions of soil, for exhaustion or otherwise, to which the re- 

 sults yet to be recorded are in all probability due. In this review 

 we shall have perhaps still clearer evidence than has been already 

 adduced, of how utterly unavailing is a liberal provision of the 

 necessary mineral constituents in the soil to give even a moderate 

 crop of barley, unless there be at the same time, within the soil, 

 available nitrogen. 



The first set of collateral experiments to be noticed is one in 

 which barley was taken successively from the same land, in the 

 seasons 1853, 1854, and 1855 respectively, after ten successive 

 crops of turnips, which had been grown experimentally with 

 different manures. 



Accordingly, in Table XII. we have the produce of barley as 

 under : — 



1st. On a plot where turnips had been grown for ten years, and 

 in the last seven without any manure whatever ; the unmanured 

 produce, leaf and bulb together, averaging little more than two 

 tons per acre per annum. 



2nd. On a plot, comprising several, which respectively had 

 liberal supplies of different mineral manures only, every year 

 during the last eight of the growth of the turnips. The produce of 

 the turnips was here much greater than on the unmanured plot. 

 On some portion of this and the following plots all, and on other 

 portions only some, of the mineral constituents of the turnip-crop, 

 were supplied each year in much larger quantity than they were 

 taken off in the crops. The produce of the succeeding barley 

 was, however, on all so very nearly alike, that only the mean 

 produce over all, is here given. 



3rd. On a plot which had had the same various mineral manures 

 on different portions, as above, for the turnips ; and in addition, 

 during six years — 1845 to 1850 inclusive — an average annual 

 amount of about 44 lbs. of nitrogen per acre in the form of ammo- 

 niacal salts ; after which the minerals only were applied for the 

 two remaining years of roots. 



4th. On a plot which had had the same set of mineral manures 

 as Nos. 2 and 3 up to the end of the turnip experiments, and an 

 average annual addition during tlie six intermediate years — 1845 

 to 1850 inclusive — of about 95 lbs. of nitrogen in the form of 



