204 The Rotkamsted Grass Experiments. 



recovered in much greater proportion than the nitrogen, but 

 not in so large a proportion as the potash ; it, too, like potash, 

 is but little subject to loss by drainage. 



The much less immediate effect of a given amount of 

 nitrogen when supplied in farmyard manure than when in 

 ammonia-salts or nitrate of soda, the consequent necessity to 

 supply so much more in that form to obtain a given result, 

 and the very slow action of the remaining residue, are 

 important factors in the scientific explanation of the prac- 

 tically recognised much lower money value of a given amount 

 of nitrogen so supplied. 



Reverting now to plot 1, the results on which have already 

 been given in Table XL VII., page 190, it remains to point out 

 the difference in effect when, besides the farmyard manure, 

 2001b. of ammonia-salts were also annually applied per acre, 

 both over the eight years of the application of the farmyard 

 manure, and over the next twelve years of the action of the 

 residue. 



The ammonia-salts caused the herbage to assume a darker 

 green colour ; gramineous species became more, and both 

 leguminous and miscellaneous species less prominent, than 

 either on the unmanured plot 3, or on plot 1 with farmyard 

 manure alone. Compared with the latter, in the early years, 

 Poa trivialis and Bromus inollis were even more prominent, as 

 also was Dactylis glomerata, and these three grasses made up a 

 large proportion of the total produce. During the later years, 

 as on the plot without ammonia, but in a greater degree, 

 Agrostis vulgaris and Holcus lanatus became very prominent, 

 as also did Anthoxanthum odoratum and Festuca ovina; 

 whilst, on both plots, Poa trivialis, Bromus inollis, and 

 Dactylis glomerata diminished very much. Of leguminous 

 plants, Lathy rus pratensis is the most prominent on both 

 plots, but much more so on plot 2 than on plot 1 ; and, whilst 

 without ammonia (plot 2) there was nearly 1 per cent, of 

 Trifolium pratense, with it there was none. A much greater 



