1917] Lipman-Gericlce : Smelter Wastes and Barley Growth 529 



considerable portion of its organic-matter supply and therefore 

 possesses a much smaller surface for adsorption of MnSO^ 

 Hence the usable portion of the soil solution would tend to 

 become more concentrated with respect to that salt and induce 

 depressions in yield of roots and grain. By the time the third 

 crop is planted, thorough oxidation of the MnSO^ has occurred 

 and most of the manganese is rendered insoluble, thus leaving 

 again only a small quantity of the salt in the soil solution. This 

 acts as a stimulant, as it did in the first crop, and induces an 

 increased yield again. This explanation, while open to question 

 in one or two important respects, may prove of some assistance 

 in the ultimate clearing up of the somewhat perplexing facts 

 which are here considered. Other explanations, involving the 

 relationship of MnSO^ to the soil colloids and to other phases 

 of the soil solution besides that above mentioned, offer them- 

 selves at this time, but they must all await the further study of 

 fundamental principles of plant physiology before they can be 

 considered to advantage. Irrespective of the theoretical argu- 

 ments which may account for the results obtained in the MnSOi 

 series, the striking facts relating to the changes in effect on 

 three successive crops of a given salt application made prior 

 to the first planting are of great practical moment. Not only 

 do they render of doubtful value for practical purposes one 

 season's results on the effects of salts on crops, but they cause 

 one to wonder if anything less than five successive crops should 

 ever constitute sufficient evidence upon which to base a judg- 

 ment. Taking all of our results together, it may be said in 

 general that MnSO^ is to be regarded, for a limited period at 

 least, as definitely stimulating to barley growth in soils. 



Manganese Chloride 

 As pointed out above, MnCL was tested along with MnS04, 

 so that manganese in different compounds might be studied for 

 itself as well as in comparison with other elements. The experi- 

 ment was arranged similarly to that of the MnS04 series, and 

 details with respect to it, together with the results obtained, are 

 set forth in tables Xa, Xh, and Xc for the three crops grown. 



