184 Agricultural Section [pt ii 



afterwards the improvement effected can be most economically 

 maintained by the moderate use of feeding cakes, etc. 



No further general rules for manuring can be usefully given 

 here. The local and special conditions to be met must be duly 

 considered in each case. 



The Effects of Manures 1 upon the different grasses. While a 

 considerable amount of information has been obtained with 

 regard to the general effects of the various common fertilisers 

 upon the composition of the turf of pastures and meadows, our 

 knowledge of the precise action of each upon the different species 

 is very small. Only in a few experiments — notably those at 

 Rothamsted — has any serious attempt been made to discover 

 which grasses tend to increase or decrease under any definite kind 

 of manurial treatment. Although these few experiments are of 

 great value, we must be careful not to generalise from them too 

 much since the composition of the original turf will greatly modify 

 the ultimate effect of manures. For in speaking of the effect of 

 any special fertiliser we must bear in mind that this is to a large 

 extent dependent upon the particular association of plants composing 

 the turf. 



With different associations of plants (and on different soils) 

 rather different results or effects will be produced by the same 

 kind of manuring. It is the finely adjusted "balance of equi- 

 librium" in the natural struggle for existence which is upset by 

 any particular manurial treatment. 



Bearing these precautions in mind we may briefly consider 

 what is known about the effects of fertilisers on (1) the vegetation 

 as a whole, and on (2) the more common grasses individually. 



Numerous experiments have shown that one of the general 

 effects of manuring (or otherwise improving the soil) is to reduce 

 the number of species present, or at least to cause a few kinds to 

 become predominant. This is especially noticeable on the more 

 inferior kinds of soil where a relatively large number of species 

 make an almost equal contribution to the annual crop. At 

 Rothamsted on the permanently unmanured hay plots the number 

 of species present was about fifty, while on some of the manured 

 plots this number fell to twenty or even less. The same fact 

 1 See also Bibliography, Nos. 6, 11, 12, 16 and 27. 



