160 EXPERIMENTS UPON GRASS LAND 



which has an opportunity to develop because it is not crushed 

 out by the competition of taller-growing herbage, such as is 

 found with the bigger crop on Plot 7. The characteristic 

 weeds of this plot are the Buttercup, 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 the most abundant grass is Quaking Grass, 

 and where weeds, chiefly Hawkbit, Burnet, and Plantain, 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 appHcation 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 l;)ecome ; 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, Fis;. 21, shows the effect of the mineral manm-es, 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 lb. of nitrogen are added ; and on Plot 11-1 

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

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

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

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



