CHAPTER XL 



GRASS-LAND WEEDS. 



THE consideration of the weeds of grass-land presents a very 

 different problem from that of arable weeds because of the 

 totally different nature of the crop with which the weeds are 

 associated. Arable land crops are, so to speak, alien to their 

 situation and are grown on bare soil, which offers a clear 

 field for the competition of other species that are native to the 

 soil and would carry all before them if they were not hindered 

 by cultivation. On grass-land, on the contrary, the crop con- 

 sists of an association of plants that are usually themselves 

 native to the soil and that grow in a closely interwoven mat 

 covering the surface of the ground, thus excluding all plants 

 that cannot make headway against keen competition. Then 

 again, on arable land it is only the produce of the sown seed 

 that is of use as a crop, whereas on grass-land it matters little 

 what particular species enter into the composition of the 

 herbage provided that they are not injurious or poisonous and 

 that the feeding value for stock is high. Consequently in 

 many cases it is not possible to draw a sharp distinction be- 

 tween the crop plants and the weeds, as a species that is quite 

 a useful constituent of herbage in one place may be a veritable 

 pest elsewhere. Whether it be mown for hay or grazed, 

 herbage typically consists of a mixture of grasses, leguminous 

 plants, and miscellaneous species from other orders. Each of 

 these groups contains some plants that are most valuable from 

 the farmer's point of view but others that are regarded as 

 of little use or as harmful weeds. The criterion is usually 

 the feeding value of the plant but this varies with circum- 

 stances, as it is influenced by soil conditions, climate, and 

 other factors, concerning which our knowledge is very imper- 

 fect. For instance, on Romney Marsh 1 adjacent fields are 



1 Hall, A. D., and Russell, E. J. (1911), "A Report on the Agriculture and 

 Soils of Kent, Surrey, and Sussex," p. 60. 



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