82 RESULTS WITH GRASS 



application of particular manures has effected. The unmanured 

 plot is the one which exhibits the greatest variety of herbage. 

 Every manure tends to simplify the produce, one or more 

 species of plant becoming prominent, while other species 

 disappear. 



As different manures thus produce hay of a different botan- 

 ical character, it becomes difficult to ascertain with accuracy 

 the comparative value of particular manures, the mere weight 

 of hay obtained being insufficient to answer the question. 



It may be stated generally that the use of lime, chalk, or of 

 cinereal manures supplying potash, tends greatly to increase 

 the proportion of leguminous plants, as white clover, red 

 clover, trefoil, and meadow vetchling ; while a heavy dressing 

 of nitrogenous manure, and especially of ammonia salts, applied 

 with or without ash constituents, tends, on the other hand, to 

 the development of a purely grass herbage, the clovers, vetches, 

 and some of the weeds, disappearing. 



In a pasture, a liberal development of the clovers, with an 

 absence of weeds, constitutes the highest class of herbage, 

 the one having the greatest feeding value for stock ; to apply 

 ammonia salts to such a pasture would entirely spoil it. In 

 a hay meadow the case is quite different ; here the weight of 

 the hay crop is the primary object, and a heavy weight of hay 

 is only to be obtained by a luxuriant growth of grass, for the 

 production of which ammonia salts are well fitted. Temporary 

 grass land, in the case of which there is no time to develop a 

 fine pasture, may also often be advantageously treated with 

 ammonia salts. 



i. Experiments at Rothamsted. A portion of the 

 Old Park, which has certainly been in grass for three centuries, 

 is divided into plots, and has been treated continuously with 

 various manures since 1856. The superphosphate and the 

 alkali salts are usually applied as a top-dressing in January, 

 the 400 Ibs. of ammonia salts are put on towards the end of 

 February. 



Owing to the small percentage of carbonate of lime 

 originally in the soil, and its removal by the ammonia salts 

 (see p. 27), it has become necessary in the later years of the 



