160 EXPERIMENTS UPON GKASS LAND 



characteristic leguminous plant is the Lathyrus pratensis. 

 The characteristic weeds of this plot are the Hawkbit, the 

 Black Knapweed, Plantain, and Yarrow ; see photograph, 

 Fig. 22. 



Plot 4-1, which each year has received superphosphate only, 

 now presents a very impoverished appearance, and is giving very 

 little more crop than the unmanured plots. Indeed, the aspect 

 of this plot, where weeds, chiefly Hawkbit, Burnet, 

 Plantain, Knapweed, and Yarrow, are unusually prominent, 

 would seem to indicate that the land is more exhausted here 

 than on the unmanured plot. It is not uncommon to find 

 cases where the application to grass land of a purely phosphatic 

 manure, like superphosphate or basic slag, is followed by a 

 great increase of crop, the addition of the phosphoric acid to 

 the dormant nitrogen and potash in the soil having supplied 

 the missing element in a complete plant food. The result, 

 however, of this plot shows how disastrous a continuation 

 of such one-sided manuring may become ; a nitrogenous 

 manure alone is often thought exhausting, but probably 

 a phosphatic manure used singly will even more quickly 

 impoverish the soil. The photograph, Fig. 23, shows the 

 impoverished and weedy aspect of this plot in 1903. The 

 diagram, Fig. 21, shows the effect of the mineral manures, and 

 particularly of potash, both with and without nitrogen, on the 

 yield of grass. 



IV. Complete Manures Nitrogen and Minerals. 



Four of the plots receive a complete artificial manure. On 

 all of them the mineral manuring is the same, and supplies 

 both phosphoric acid and potash ; on Plot 9, ammonium-salts 

 containing 86 Ib. of nitrogen are added; and on Plot 11-1 

 the amount of ammonium-salts is increased by one-half, 

 to 129 Ib. of nitrogen. Plot 14 receives 86 Ib. of nitrogen 

 as nitrate of soda, and therefore compares with Plot 9. 

 Plot 16 also receives nitrate of soda, but only half the 

 amount on Plot 14. Considering Plots 9 and 11-1 first, it 



