120 RESULTS WITH TURNIPS 



that a full crop being obtained without ammonia, the 

 addition of ammonia was superfluous and produced no effect. 

 That the crop was already a maximum one was further shown 

 by the fact that doubling the dung also occasioned no further 

 rise in the produce. Again, in the Glasgow and West of Scot- 

 land experiments, the average result on 9 farms in 1893 shows 

 no gain by adding f cwt. of sulphate of ammonia to 6 cwts. of 

 superphosphate used without dung ; but in the following year 

 the average result on 15 farms was a gain of 46^ cwts. of roots 

 by this small addition of ammonia. The first set of experiments 

 was made in what is described as a very good season, the crop 

 grown by 6 cwts. of superphosphate alone amounted on an 

 average to 24 tons 14 cwts. of roots. In the second season the 

 same quantity of superphosphate yielded 18 tons 9 cwts. There 

 was thus in the latter case an opportunity for further increase 

 by the use of an ammoniacal manure. 



The amount which constitutes a full crop of turnips in any 

 season is limited by the physical condition of. each soil, by the 

 supply of water, and by the sunshine and temperature which 

 occur during the growing period. No supply of plant food can 

 push the crop beyond the limits assigned by these conditions. 



A soil equally fertile as those of the Welsh and Scotch 

 farms just referred to may yield an excellent return from sul- 

 phate of ammonia when the conditions admit of a larger pro- 

 duce. At Cockle Park, in Northumberland, in 1896, the pro- 

 duce obtained from 10 cwts. superphosphate, and 2 cwts. 

 sulphate of potash was 21 tons, 15 cwts. of Yellow Turnips ; 

 when to this manure i cwt. of sulphate of ammonia was added 

 the crop became 26 tons 8 cwts. ; when 2 cwts. sulphate of 

 ammonia were employed the crop reached 30 tons 16 cwts. 

 Here there was an unusually excellent return from the am- 

 monia, notwithstanding the largeness of the crop grown without 

 nitrogenous manure. 



The size of a crop is not only limited, as we have already 

 seen, by the external conditions which attend its growth, it may 

 also be limited by the scanty supply of an essential part of its 

 plant food. In the culture of turnips at the present day it is an 

 almost universal practice to employ a manure supplying phos- 



