158 EXPERIMENTS UPON GRASS LAND 



paper. So pronounced had this effect become on Plot 5, 

 which received the larger amount of ammonium-salts, that the 

 application has been discontinued since 1897, lest the turf 

 should be entirely killed. Another sign of the sourness 

 caused by the use of ammonium-salts without minerals is 

 seen in the prevalence of Sorrel on this plot ; it forms nearly 

 15 per cent, of the whole herbage, and it is interesting to note 

 that the only portion of the plot from which the Sorrel is 

 absent is a strip that was dressed with chalk in 1883 and 1887. 

 The aspect of the plots receiving only nitrogenous manure 

 shows very characteristic differences ; both possess a very dark 

 green unhealthy colour, but, while the ammonium plot seems 

 in the main to be clothed with Sheep's Fescue and other 

 grasses, amounting to 77 per cent, of the whole, the nitrate of 

 soda plot possesses a much more varied herbage, of which 

 weeds form 30 per cent. Leguminous plants are practically 

 absent from both, plots, though a small proportion may be 

 found where the nitrate of soda is used. The impoverish- 

 ment due to the continual use of a manure like nitrate of 

 soda supplying one element only of plant food is to be seen 

 in the gradual decline of production on Plot 17, and in the 

 present predominance of weeds there. Considering, however, 

 the length of time that nitrate has been used on this plot, 

 the crop has been wonderfully maintained ; the deep root- 

 range induced by the solubility of the nitrate enables the plant 

 to feed widely in the soil, and the soda base assists in bringing 

 the dormant potash into a form available for the plant. The 

 photographs, Figs. 18 and 19, show the characteristic appear- 

 ance of the turf from Plot 5, with ammonium-salts alone, and 

 Plot 17, with nitrate of soda alone. 



III. Mineral Manures used alone. 



On three of the plots no nitrogenous manures have been 

 applied since the beginning of the experiments. On Plot 7 

 a complete mineral manure, supplying phosphoric acid, potash, 

 magnesia, and soda, is used; Plot 8 has received the same 



