NITRATE OF SODA V. AMMONIUM-SALTS 163 



the great excess of nitrogen applied to this plot, any substance 

 like soda, which supplements and economises the potash avail- 

 able, will be of service to the plant. 



Turning now to Plot 14, which receives the same manure 

 as Plot 9, but with its nitrogen in the form of nitrate of soda, 

 we notice first that the nitrate of soda has been the more 

 effective source of nitrogen, giving an average crop of 56 cwt. 

 against 54 cwt. with ammonium- salts. The superiority of the 

 nitrate of soda has been most pronounced in dry seasons, 

 owing to the generally deeper-rooted habit of the grasses found 

 on this plot. 



During the great drought of 1870, holes were dug for the 

 examination of the subsoil on this plot and on Plot 9. On the 

 latter, where ammonium-salts formed the source of nitrogen, 

 very few roots could be distinguished below 36 inches, and the 

 subsoil below 27 inches seemed to have been but little changed 

 by the development of roots and their decay. On Plot 14, with 

 the nitrate of soda, wiry roots extended nearly to 4 feet, and the 

 subsoil down to 4 feet 6 inches had suffered a marked change. 



The vegetation on plots grown with nitrate of soda is more 

 varied, nor. are the leguminous plants so completely suppressed 

 by the large amount of nitrogen. This plot, for example, 

 showed in 1903 more than 3 per cent, of Meadow Vetchling 

 and a trace of White Clover. The aspect of the nitrate and 

 ammonia plots is strikingly different, as may be seen by com- 

 paring the two photographs taken in 1903, Figs. 26 and 24. 

 With the nitrate of soda a great part of the herbage, 23 per 

 cent., was composed of Soft Brome in 1903, but only 5 per 

 cent, in 1914 ; this grass is hardly to be found on any of the 

 other plots. Again, Beaked Parsley is very prominent, though 

 it is hardly to be found on any of the other plots ; it constituted 

 10 per cent, of the herbage in 1903, but 1 per cent, in 1914, so 

 that just before hay time the whole plot showed white with its 

 flowers In addition to the Soft Brome, the grasses which pre- 

 dominate are Meadow Foxtail, False Oat, and Sheep's Fescue. 



Plot 16, which receives the smaller quantity of nitrate of 



