524 University of California Puhlications in Agricultural Sciences [Vol. 1 



In the second crop, on the other hand, as in the first, the larger 

 amounts of potash alum were neither inferior nor superior to 

 the smaller amounts in increased production of straw and grain, 

 but were of about the same influence throughout. Consistent 

 with the effect of potash alum on the straw and grain yields was 

 that on the root yields. The latter were, throughout the whole 

 series in the second crop, increased by the potash alum applica- 

 tions and, as in the cases of straw and grain, independently 

 of the amounts of potash alum employed. We have, therefore, 

 another phase of analogy between the potash alum and the 

 CUSO4 series in the second crop which seems only to make the 

 resemblance stand out in greater relief. The production of 

 every part of the plant in the second crop was stimulated by 

 both potash alum and by CuSO^, but not by the other sulfates 

 employed. 



Third Crop 



Wliolly at variance with tlie effects just noted are those 

 observed in the third crop of the potash alum series. So far 

 from stimulating the growth of barley in all respects, as it did 

 in the first and second crops, and particularly in the latter, 

 potash alum in any and all concentrations depresses the growth 

 of barley when the yields of total dry matter are used as a basis 

 of comparison. This is true also for the straw and root yields 

 taken separately, with the possible exception of the straw yield 

 with the lowest concentration of potash alum. In the case of 

 the grain yields, however, no indubitable evidence of a depress- 

 ing effect by the potash alum is at hand. It is indeed not im- 

 possible that definite though small effects of potash alum stimu- 

 lating to grain production in the third crop might be allowed in 

 some of the concentrations of the salt employed. The explana- 

 tion of this striking change in the effects of potash alum in two 

 successive crops is obviously not simple, though several possible 

 explanations immediately suggest themselves. It is probable 

 that the most favorable explanation would be over-stimulation 

 of plant growth in the first two crops and the removal of most 

 of the easily available bases in the soil, leaving an impoverished 

 soil condition and perhaps a so-called "physiological acidity," 



