IMPROVEMENT OF GRASS LAND 145 



1856 and not grazed since 1874,* it has been observed 

 that on the unmanured plots " there is no sign of 

 approaching exhaustion or great falling off in crop 

 from year to year." Yet there is an impoverishment 

 which " is more to be seen in the character of the 

 herbage than in the gross weight of the produce. 

 Weeds of all descriptions occupy the land, and the 

 relative proportion they bear to the grasses and 

 clovers has increased from year to year ; of late years 

 weeds have formed nearly one-half of the herbage." 

 The most prominent species among the weeds were 

 Burnet, Hawkbit, and Black Knapweed. 



Where nitrate of soda only was regularly applied, 

 there appears to have been a gradual increase in the 

 percentage of weeds present, weeds forming in 1905 

 40 per cent of the herbage, while leguminous plants 

 were practically absent, and deep-rooting grasses, like 

 meadow foxtail and downy oat-grass, were promi- 

 nent. At the same time, there was a great increase in 

 the yield of hay compared with the unmanured plots. 



With a continual application of ammonium salts alone, 

 the increase in crop, compared with the unmanured 

 plots, has been much less than with nitrate of soda. In 

 addition, shallow-rooted plants have been encouraged 

 until " the plots receiving only ammonium salts are 

 almost wholly occupied by Sheep's Fescue and Com- 

 mon Bent." On one plot Sorrel formed nearly 15 per 

 cent of the whole herbage ; and on this plot the con- 

 tinued action of the ammonium salts was so harmful, 

 that the application was discontinued in 1897 "lest the 

 turf should be entirely killed." 



Three plots received mineral manures only, and where 

 a supply of phosphoric acid, potash, magnesia, and soda 

 has been given there has been no sign of declining fer- 



1 A. D. Hall, The Book of the Kothamsted Experiments, 1905. 



K 



