528 University of California Publications i7i Agricultural Sciences [Vol. 1 



different from it in several important particulars. As a general 

 thing, the other salts still give more stimulating effects in the 

 second crop so far as the total dry-matter production is con- 

 cerned, but this is not true in any instance of the second crop 

 of the MnSO^ series. It sliould be borne in mind, however, that 

 the manganese series is not comparable with the others except 

 possibly with the lead series, because only one treatment, prior 

 to the first crop, was given. 



Third Crop 



The depressing effect exerted by MnS04 in the second crop 

 of barley, at least so far as the grain and straw yields are con- 

 cerned, appears to have been merely an ephemeral one. There 

 was not only a total disappearance thereof in the third crop, 

 but an actuallj^ stimulating effect seems to liave replaced it ; and 

 to have extended to straw, grain, and root production and was 

 not confined, as in the second crop, merely to straw production 

 in part of the series. Moreover, the stimulating effect of the 

 MnSO^ appears to have extended throughout all concentrations 

 and would seem to have been greatest at the medium high con- 

 centrations, as is indicated in table IXc. While much better 

 agreement between duplicate determinations could have been 

 desired, the clear superiority in yield of the majority of treated 

 pots, when compared with the controls, leaves scarcely any room 

 for doubt that we are here confronted with real cases of stimu- 

 lating effects. The results are the more interesting and striking 

 since large concentrations of MnSO^ are involved. The results 

 call for further observations on the apparent reversal of results 

 between the second and third crops and between the second 

 and first crops. Unfortunately, no definite leads are in our pos- 

 session which would aid us in answering this question. Theo- 

 retically, however, it would seem possible to explain the facts 

 as follows : In the first crop the large quantity of organic matter 

 present in the soil brings about the adsorption of the JMnSO^ 

 and leaves the active soil solution relatively dilute in that salt. 

 This low concentration acts as a stimulant to both the higher 

 plants and the soil flora and induces an increased yield. After 

 one season of exposure to sun and cultivation, the soil loses a 



