Continuous Growth of Herbage without Manure. 145 



the mean indications of the two unmanured plots. Hence, 

 unless otherwise stated, all comparisons are made with the 

 produce of the unmanured plot 3. 



The reduction of produce on the continuous growth without 

 manure is, apart from influences of the seasons, attributable 

 in part to deficiency in available nitrogen, but probably in 

 greater degree to that of an available supply of potash, of 

 phosphoric acid, and of silica. In the absence of manure 

 favouring any particular species or families of plants, no 

 artificial struggle for existence was induced among the 

 herbage, and the result was that a greater variety of species 

 maintained their position than on any of the manured plots. 

 The proportion of grasses was comparatively low; that of 

 leguminous plants was fairly high ; but the most marked 

 characteristic was the large number, and high proportion by 

 weight, of the .miscellaneous species (weeds). Under this 

 varied crop there is a much greater annual assimilation of 

 nitrogen, and of some of the most important mineral 

 constituents over a given area, than in an unmanured 

 gramineous crop, such as wheat or barley, grown separately, 

 on arable land. 



2. Ammonia-Salts Alone : Plot 5. The results shown in 

 Table XXXI. were obtained by the annual application of 

 ammonia- salts alone, at the rate of 4001b. per acre per 

 annum, estimated to supply about lOOlb. of ammonia, corres- 

 ponding with about 821b. of nitrogen ; for comparison, the 

 results on plot 3, without manure, are also given. 



Compared with the produce without manure, ammonia- 

 salts have given an average annual increase over twenty years 

 of 5631b. of hay, or, in all, ll,2601b., or rather more than five 

 tons, the extra demand for mineral constituents being met 

 solely by the soil. But the falling off in increase as time 

 went on is very marked. Actually less lime and potash were 

 taken up with the ammonia than without manure, which 

 appears due to the fact that, under the influence of the 

 purely nitrogenous manure, various species which com- 



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