108 RESULTS WITH MANGELS 



especially of potash, if the ammonia is to produce its full 

 effect, is strikingly shown in these experiments. The am- 

 monia salts used alone, on a plot exhausted of ash con- 

 stituents, produce only 7 tons of roots. The addition of 

 superphosphate raises this to 8f tons. The further addition 

 of alkali salts increases the crop to 16 tons. That potash 

 was the most important constituent of the alkali salts used is 

 proved by a further experiment not quoted in the table ; in 

 fact, the omission of the sulphate of magnesia and common 

 salt from the manure diminished the crop by only i ton 4 cwt. 

 On a series of plots receiving a double amount of nitrogenous 

 manure (both ammonia salts and rape cake), the addition 

 of sulphate of potash to the superphosphate more than doubled 

 the crop. 



The crop produced by 14 tons of farmyard manure very 

 little exceeds that obtained from 400 Ibs. of ammonia salts 

 with ash constituents. The addition of 400 Ibs. ammonia 

 salts to the dung increases the crop by 5 tons iScwts. of roots. 

 This increase is clearly much less than that obtained from the 

 same quantity of ammonia salts on the plots well supplied with 

 ash constituents. It is probable that the potash supplied by 

 the farmyard manure was insufficient for this abundant nitro- 

 genous manuring. The addition of superphosphate to the 

 mixed farmyard manure and ammonia salts produced no 

 increase in the crop. 



Some German investigators have recently called attention 

 to the smaller return obtained from ammonia salts when these 

 are used together with farmyard manure, and they regard this 

 result as due to a destruction of the nitrates formed from the 

 ammonia, or even to a destruction of the ammonia itself, by 

 means of micro-organisms contained in the farmyard manure. 

 We cannot here enter fully into this question, which will be 

 found thoroughly discussed in the pages of the Royal Agricul- 

 tural Society's Journal, 1897, 577> but we may mention that with 

 farmyard manure and ammonia salts used as in the Rothamsted 

 experiments, there is no evidence whatever of a loss of nitrogen 

 from the ammonia. The quantity of nitrogen contained in the 

 root and leaf produced on the mangel plots was determined for 



