164 The Rothamsted Grass Experiments. 



of about 81b. more silica annually taken up on the straw plot, 

 but less over the second period than the first. 



Some of the increased luxuriance under the influence of 

 the straw manuring is probably attributable to an increased 

 supply of manurial constituents, and some to the mechanical 

 effects (e.g., the " mulching " effect, or protection given by 

 the straw to the young shoots). And something is due, 

 perhaps, to the greater powers of food collection within the 

 soil of the species favoured. 



9. 800Z6. Ammonia-salts with Mixed Mineral Manure con- 

 taining Potash: Plots Ha and 116. These plots show the 

 effects of a considerably increased supply of ammonia-salts, 

 used in conjunction with the same mixed mineral manure, 

 including potash, as on plot 9. During the first three years 

 double the amount, or SOOlb. per acre, of ammonia-salts, 

 containing about 2001b. of ammonia, equivalent to about 

 1641b. of nitrogen, was annually applied. This quantity, 

 from its effects, appearing excessive, was then reduced to 

 one-half, or to the same as on plot 9, for three years ; but as 

 it then appeared that the maximum growth possible was not 

 attained, the quantity was again doubled, and has continued 

 so. At the period of this change, too, i.e., after the first six 

 years, the plot (11) was divided, and to one-half, in addition 

 to the ammonia-salts and the usual mixed mineral manure, 

 artificial silicates were thenceforward applied ; for nine years 

 (1862-70), 2001b. of a crude silicate of lime, and 2001b. of a 

 crude silicate of soda, and afterwards 4001b. of the silicate 

 of soda, per acre per annum were employed. The results are 

 summarised in Table XXXIX. opposite. 



Thus an increased supply of ammonia-salts with the same 

 mineral manures as on plot 9, has considerably increased the 

 annual produce of hay, but in a much greater degree the 

 assimilation of nitrogen, over a given area; and it has 

 increased, in about the same proportion as the increase of 

 hay, the amount of total mineral matter taken up over that 

 on plot 9, where the same amount was applied by manure. 



