PRINCIPLES OF AGRICULTURAL CHEMISTRY 



it is evident that the higher percentage of potash did not con- 

 tribute to a greater production of straw. That is to say, 

 plants may take up a considerable excess of plant food, especially 

 of potash. 1 



The influence of the season upon the ash content of plants is 

 illustrated by the same series of analyses referred to above, 

 namely, barley grown on the experimental plots of the Rotham- 

 sted Experiment Station. The differences between the average 

 composition of the ash of plants from plots differently manured, 

 show the effect of ihe application of plant food. The differ- 

 ences between the highest and lowest content of ash for the same 

 manure, show the effect of the season. The results in the follow- 

 ing table are expressed in terms of the plant instead of the ash as 

 in previous tables. 



EFFECT OF MANURES AND THE SEASON ON POTASH AND PHOSPHORIC 

 ACID CONTENT OF BARLEY. 



Both fertilizer and season have comparatively little effect upon 

 the composition of the grain, as we have observed before. On 

 the straw, the season has a greater effect than the fertilizer. For 

 example, the average potash in the unmanured straw is to the 

 potash in the manured straws as 8.60:14.10 or less than 1 :2, while 

 in different seasons the straw grown on the manured plot varied 



1 See also Wilfarth and Wimmer, Exp. Sta. Record 13, 1030. 



2 Bulletin 22, Office of Exp. Station, p. 75. 



