XIII.] FERTILISERS FOR GRASS LAND 265 



The manuring of grass land is too big and 

 complicated a subject to be dealt with here in any 

 detail. Very often indeed the grass land receives no 

 artificial manure at all; the farmer trusts to the 

 fertilising effects of the cake and other foods consumed 

 by stock on the land to maintain its fertility, even when 

 he grazes it one year and lays it up for hay the next. 

 It will, however, be found more profitable to hay the 

 same land every year and keep up its fertility by 

 manuring because in that way the growth of the 

 stronger grasses which go to make a big hay crop is 

 encouraged, whereas they are repressed by a summer's 

 grazing and their place more or less taken by smaller 

 bottom herbage which cannot figure largely in the hay 

 crop. Speaking generally, when supplying manure for 

 hay we want to remember that nitrogenous manures 

 will promote the growth of grasses at the expense of the 

 other constituents of the herbage, until, as we see on 

 some of the Rothamsted grass plots, the continuance of 

 a nitrogenous manure year after year for a long period 

 will cause the whole herbage to be made up of grass 

 alone. On the other hand, phosphates and potash 

 without nitrogen stimulate the development of clovers 

 and other leguminous plants. The herbage is not so 

 bulky, but weight for weight is more valuable as food for 

 stock. Thus a manure for hay should contain nitrogen 

 in order to get bulk, but should also contain a due 

 proportion of phosphates and especially of potash, to 

 keep up the clovers and to give feeding value to the 

 products. On pasture land we want chiefly to encourage 

 the clovers, and therefore use fertilisers containing no 

 nitrogen — either basic slag alone when the land is rich 

 in potash which the lime in the basic slag will liberate, 

 or basic slag and kainit on the lighter soils. If we can 

 only encourage the growth of the clovers in the pastures 



