IN THEIR ACTION UPON WHEAT. 207 



TotaJ Increased produce for 100 Ib. of nitrogen, 



nitrogen applied. Grain. Straw. Total. 



Ib. lb. Ib. Ib. 



2. 191 2041 2964 5005 



3. 47J 1335 1661 2996 



4. 67 1083 1713 2796 



The rape-cake used alone, in the second experiment, gave an 

 increased produce both of grain and straw more than one-half 

 greater in proportion to its nitrogen than the sulphate of am- 

 monia, when applied alone, in the third experiment. And, 

 when the two substances were used together, the produce of 

 grain was still less from a hundred of nitrogen than when the 

 sulphate was used alone. 



In so far, therefore, as the experiments detailed in the pre- 

 sent section are worthy of reliance and in the absence of dupli- 

 cate trials, we must not rely too confidently upon them it ap- 

 pears that the sensible effect of an organic substance containing 

 nitrogen on the quantity of a crop to which it is applied, is by 

 no means indicated by the proportion of nitrogen it is known to 

 contain. We saw reason in the preceding section to conclude 

 that such was the case, also, with the salts of ammonia when 

 compared with each other, and with the nitrates compared 

 among themselves, or with the salts of ammonia. It is, there- 

 fore, probable that every substance which contains nitrogen 

 exercises upon growing plants an action peculiar to itself in 

 quality and in intensity. The nature and amount of this special 

 action can only be made clear by further experiments specially 

 directed to this end. 



3. Influence of the quantity of nitrogen, and of the state of che- 

 mical combination in which it exists in a fertilising substance, 

 on the quality of the crop to ivhich it has been applied. 



But if the quantity of a crop is not directly as that of nitro- 

 gen in the manure, is not the quality determined by the amount 

 of nitrogen applied to the land ? This opinion was formerly 

 entertained, but it will not bear the test of rigorous investiga- 

 tion. I have elsewhere discussed this subject;* but some 



* Lectures on Agricultural Chemistry) 2d edition, p. 874. 



