206 RAPE-CAKE COMPARED WITH AMMONIA 



rape-cake gave a much greater increase, in proportion to the 

 nitrogen it contained, than the sulphate of ammonia ; second, 

 that the addition of sulphate of ammonia actually diminished 

 the natural effect of the rape-cake in No. 6, compared with No. 

 4, in both of which cases 18 cwt. of rape-cake were applied ; 

 and third, that the sensible effects of the rape-cake when used 

 alone in the two experiments, 3 and 4, was nearly in propor- 

 tion to the quantity applied. 



c The opinion entertained by some writers on this branch of 

 science that the nitrogen contained in rape-cake and other 

 organic substances only becomes valuable or available to plants 

 when it is decomposed and converted into ammonia in the soil 

 or elsewhere is inconsistent with we may say, is directly con- 

 tradicted by the above experiments. If one hundred pounds 

 of nitrogen, already in the form of ammonia, (in the sulphate of 

 ammonia,) produced in the seventh experiment only 3 tons 8 

 cwt., while an equal weight, in the form of rape-cake, produced 

 22 or 23 tons, it is clear that some other virtue yet unrecognised 

 must reside in the constituents of rape-cake. And if in this, 

 similar virtues may reside also in other organic substances, of 

 which nitrogen forms a constituent part. 



3. With rape-cake, compared with sulphate of ammonia, 

 upon ivheat. In 1846, Mr Lawes employed these substances in 

 comparative experiments upon wheat (old red Lammas variety) 

 sown upon a piece of exhausted land, to which no manure had 

 been previously applied, with the following results : 



Grain. Straw. 



bush. Ib. Ib. Ib. 



1. No manure gave . . 17^ or 1216 1455 2671 

 2. Rape-cake, 4 cwt. . . 23^ or 1614 2033 3647 

 3. Sulphate of ammonia, 2 cwt. 27^ or 1850 2244 4094 



4. Rape-cake 4 cwt. i 28| or 1942 2603 4545 



Sulphate of ammonia, 2 cwt. j 



The small comparative effect of the two substances, applied 

 together in the fourth experiment, is striking enough ; but the 

 bearing of the whole results upon the influence of the nitrogen 

 will appear more clearly by showing the increase in each case 

 for a hundred pounds of nitrogen in the manure, 



