EXPERIMENTS AT ROTHAMSTED 117 



potash as well as phosphates, this dressing of ammonia salts 

 produced no increase in the weight of the roots, and indeed 

 frequently diminished the crop, but it produced a consider- 

 able increase in the weight of leaf, amounting on an average 

 of all the plots to more than two tons per acre. This action 

 of the ammonia salts demands our consideration, as it will be 

 found continually occurring in experiments on the turnip crop. 



In the life history of the turnip crop the leaf is produced 

 first, and the root is afterwards constructed out of the organic 

 matter prepared by the leaf. A turnip crop having a large 

 proportion of leaf at harvest is thus a crop imperfectly 

 developed. This imperfect development may be due to the 

 total supply of plant food being greater than the plant can 

 turn to account : and this will be especially the case in wet 

 and cold seasons, in which the vital actions of the plant are 

 depressed. The imperfect development is however more 

 frequently due to an ill-balanced food supply, and especially 

 to an excess of nitrogenous food over ash constituents. It 

 is when nitrate of soda or ammonia salts are applied alone 

 that the excessive proportion of leaf is seen in its greatest 

 extent, while this characteristic will entirely disappear if all 

 the ash constituents of the crop are supplied in proper pro- 

 portions, and the quantity of nitrogenous manure is kept 

 within the limits of profitable use. 



Many of the published experiments on the use of ammonia 

 salts for turnips are by no means fair to the manure, as they 

 give no account of the weight of leaf at harvest. The leaf is 

 of course an excellent sheep food, and its amount should be 

 taken into account in estimating the value of the crop. 



The variations in the proportion of leaf to root, due to 

 differences in the nature of the manure, are far smaller in the 

 case of swedes than in the case of turnips. 



The Rothamsted experiments on roots have not been pub- 

 lished in detail. The summaries of the earlier experiments 

 published in the Memorandum sheet do not relate to definite 

 continuous applications of ammonia. In the later experi- 

 ments with swedes the quantity of ammonia salt was far too 

 large to afford a profitable return. In the last ten seasons, 



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