NITRATE OF SODA AND AMMONIUM-SALTS 107 



remaining tufts of small leaves, which show no signs of 

 completing their growth however prolonged the season may be. 



C. Comparison of Nitrate of Soda and Ammonium- salts as 

 sources of Nitrogen. It has already been pointed out that the 

 plots of Series N cross-dressed with nitrate of soda, give 

 better crops than the corresponding plots of Series A, which 

 receive the same amount of nitrogen in the form of ammonium 

 sulphate and chloride. This is particularly the case on Plots 

 5 and 8, where no potash is added, for the soda of the nitrate 

 of soda seems to supply the alkali needed by the plant, or at 

 any rate enables it to utilise the reserves contained in the 

 soil. The superiority of nitrate of soda is, however, also very 

 evident on the other plots receiving potash or the complete 

 alkaline salts. Taking the mean of Plots 1, 2, 4, 6, and 7, and 

 comparing Series N and A, the crop obtained with 86 Ib. of 

 nitrogen in the form of nitrate of soda exceeds the crop of the 

 corresponding plots in the ratio of 100 to 89. On the 

 E-othamsted soil nitrate of soda always gives rather a higher 

 return than ammonium- salts, but not quite to the same extent 

 with other crops as with mangolds ; the superiority of nitrate 

 of soda is, however, not so marked as to suggest any specific 

 affinity of mangolds for nitrate of soda, lovers of saline matter 

 and of nitrates though they are. 



The cause of the superiority of the nitrate of soda is 

 probably to be found in the different character of the growth it 

 induces ; being freely soluble in water and not retained in any 

 way by the soil, it sinks more readily, with the result that the 

 plant develops a longer and deeper root-system to follow the 

 nutriment. Ammonium-salts, on the contrary, are immediately 

 absorbed by soil of the Rothamsted type, and are retained 

 very close to the surface ; the plant in consequence develops a 

 root-system correspondingly near the surface, and does not 

 search the subsoil so thoroughly for either food or water. 



The appearance of the mangold crop when it is ready to lift 

 also confirms the opinion expressed above, that the superiority 

 of the nitrate of soda is partly due to the increased root-range 



