134 EXPERIMENT STATION. [Jan. 



lized ones. Potato scab has been slowly working its way into 

 these plots since the experiment was started a few years ago, 

 although the seed potatoes were treated with the standard 

 corrosive sublimate solution before being planted. Notwith- 

 standing this, potato scab developed quite severely on some 

 plots, and the following table shows to what extent. No 

 stable manure has been applied to these plots, hence that 

 source of contamination has been eliminated. 



Table IV. — Showing the Development of Scab on Plots treated with 

 Different Potash Compounds. 



Fertilizer used. 



Amount of Scab 

 (Per Cent.). 



No potash, . . . . 

 Kainit 



High-grade sulfate of potash, 

 Low-grade sulfate of potash, 

 Muriate of potash, . 

 Nitrate of potash, . 

 Carbonate of potash, 

 Silicate of potash, . 



5.0 

 2.0 

 1.0 

 1.2 



95.0 

 3.0 



The above estimates of proportion of tubers affected by scab 

 is based upon observations upon the fourth and fifth series of 

 plots. The relative abundance of the disease in other plots 

 was similar, but the proportion of scabby potatoes was larger. 



The results given in this table show that there is a marked 

 difference in one instance of the development of potato scab 

 which can be traced directly to the fertilizer employed. It 

 should be noted in this connection that the results in the 

 different plots are very uniform, practically all the potatoes 

 in the carbonate of potash plots showing much scab, and it is 

 quite evident that this fertilizer is favorable for the develop- 

 ment of scab. It is also clear that the corrosive sublimate 

 method of treating the seed potatoes, as well as any other 

 similar method of treatment, is of little value when the soil 

 conditions are especially favorable for the scab fungus. The 

 muriate and nitrate of potash plots did not seem to have de- 

 veloped the scab, and undoubtedly much can be accomplished 

 in holding the disease in check by applying fertilizers which 



