On the Groioth of Barley hy different Manures, S^c. 501 



in the soil, was not equal to the annual unmanured produce in 

 the other field, where the barley was growing continuously. 



That the beneficial effect of the residue of the rape-cake was 

 not due to the mineral constituents it supplied, may be judged by 

 the fact, that the residue of the direct mineral manures had not 

 any such effect. It was undoubtedly a residue oi available nitrogen 

 within the soil, that gave the increase of produce of barley where 

 the ammoniacal salts or rape-cake had been employed for the 

 turnips. If this be admitted, we have in the facts, at once a 

 beautiful illustration of the degree of reliance upon nitrogen in 

 the soil of the turnip crop, and of the utter incapability of rich 

 supplies of mineral constituents in the soil, to be of any avail in 

 yielding agricultural quantities of barley, unless there be at the 

 same time icithin the soil, a liberal amount of available nitrogen. 



If further proof be wanted that the necessary mineral consti- 

 tuents were in abundance, and available in this turnip-exhausted 

 soil for very full crops of barley, provided only available nitrogen 

 were also within the reach of the roots of the plants, it is to be 

 found in the results of the experiments Nos. 6 and 7 (Table XII.). 

 Here ammoniacal salts and nitrate of soda respectively, were 

 added to a part of the turnip plot, where the residue of the 

 turnip mineral manures alone, had been unavailing to increase 

 the produce of barley. 



In 1853 the produce of barley on the mineral-manured turnip- 

 plots was 20^y bushels. In 1854 those portions of the mineral- 

 manured plots left without further manure gave 19^ bushels. But 

 where now (in 1854), about 82 lbs. of nitrogen per acre w^ere added 

 as ammoniacal salts, we had, instead of 19|^ bushels, 52^ bushels 

 of barley ; and where the same quantity of nitrogen was added 

 as nitrate of soda, 54| bushels. The increase in the produce of 

 straw was in greater proportion still. By the addition of the 

 ammoniacal salts, the straw was raised from 1397 lbs. per acre 

 to 4379 lbs. ; and by the nitrate of soda it was increased to 

 4781 lbs. The total produce (corn and straw together), Avas 

 thus from 3 to 3^ times as great by the simple addition of am- 

 moniacal salts or nitrate of soda. And it may be observed, in 

 passing, that here again nitrate of soda was more active than an 

 assumed equal amount of nitrogen given as ammoniacal salts. 



It is verv remarkable too, that although the produce after the 

 mineral-manured turnips was little more than half as much as 

 the unmanured produce in the field of continuous barley experi- 

 ments, yet the addition of a given amount of nitrogen gave A;ery 

 nearly identical results in both fields. Thus, after the mineral- 

 manured turnips, we had, with the ammoniacal salts and nitrate 

 of soda respectively, 7377 lbs. and 8005 lbs. of total produce 

 (corn and straw together) ; and in the field of continuous barley 



VOL. XVIir. 2 L 



