VEGETATION OF MEADOWS AND PASTURES 59 



on these plots, and the grass has been cut twice in the year. The 

 hay made has been weighed, and exact records have been kept 

 of the manure given to each plot and the yield from each. Two 

 of the plots have been left without manure during the whole 

 period ; other plots have been given nitrogenous manures entirely, 

 namely, ammonium salts and nitrate of soda. Others again have 

 been dressed with mineral manures alone ; a fourth set have 

 had nitrogenous and mineral manure. The unmanured plots 

 do not show any great diminution in the weight of the hay, but 

 the character of the grass has very much deteriorated during the 

 fifty years, and the weeds form a larger percentage than they 

 formerly did ; in 1902 they reached the high figure of 50 per 

 cent. The Quaking Grass, the Sheep's Fescue, Bird's-foot Trefoil, 

 Black Knapweed, Burnet, and Hawkbit are among the most 

 prominent weeds in these unmanured plots. 



The plots dressed with nitrogenous manures have given 

 different results according to the manure used. The average 

 yield of hay was 35 cwt. per acre when nitrate of soda alone was 

 used, and only 26 cwt. in the case of ammonium salts. On the 

 plots manured with nitrate, deep-rooting Grasses such as the 

 Meadow Foxtail and the Downy Oat Grass were conspicuous ; 

 on the plots with ammonium salts, the Sheep's Fescue and the 

 Common Bent, which have a shallower root system were 

 dominant, for the nitrate of soda sinks down into the soil, 

 whilst the ammonium salts are retained by the surface layers. 

 Leguminous plants are practically absent from these plots. 



The plots to which mineral manures alone have been given 

 have not suffered from the want of nitrogen, owing to the fact 

 that leguminous plants can use the free nitrogen of the air ; the 

 yield of hay per acre was 38 cwt. One plot to which mineral 

 manure without potash was given has shown some striking results. 

 The yield per acre is much less, owing, it is thought, to the reduced 

 percentage of leguminous plants which seem to require potash. 

 The most productive manure has proved to be, as might be 

 expected, a combination of mineral and nitrogenous substances, 

 when the yield per acre has, in some cases, reached as high a 

 figure as 72 cwt. 



Another especially interesting result is the effect of a change 



