POTATO DISEASES 1 TN I907. 317 



plots with regard to liming was as follows, given in the order 

 that the potato rows intersected the lime plots from north to 

 south: No. 1, 1000 pounds of lime; No. 2, no lime; No. 3, 

 500 pounds of lime; No. 4, no lime; No. 5, 1000 pounds of 

 lime; No. 6, no lime; No. 7, 500 pounds of lime. At digging 

 time the crop on the rows for about 12 feet either side of a 

 junction of 2 plots was discarded and the per cent of scab in 

 the remaining portion of the rows carefully determined. The 

 results obtained on similar plots were very uniform indeed. 

 The following gives the average per cent of scab on potatoes 

 from each set of plots receiving the different applications of 

 lime : 



Treatment, 1000 lbs. lime. 500 lbs. lime. No lime. 



Per cent of scab on 



potato crop, • 49 27 11 



DISCUSSION OF RESULTS. 



It would seem from this experiment that the application of 

 1000 pounds of lime per acre is likely to lead to a dangerous 

 increase in scab unless a longer period than 3 years is allowed 

 before potatoes are again used in the rotation, for there was 

 more than 4 times as much scab on these plots as on those 

 which received no lime. Five hundred pounds of lime per 

 acre increased the amount of scab nearly 3 fold. The only 

 conclusion that can be drawn from this single experiment is 

 that sufficient lime to produce marked increase in the clover 

 and grass yields is likely to also produce a marked increase 

 in scab on potatoes used in a 3-year rotation on infected soil. 

 However, it is possible that the amount of scab might be largely 

 decreased by the following procedure : First, the use of clean, 

 treated seed. Second, the season before the potato crop is to 

 be planted the clover crop could be cut early in July. The 

 second crop of clover would be allowed to grow well into Sep- 

 tember and then plowed under before being killed with frost. 

 This would riot only supply considerable fertilizing material 

 for the following potato crop but the production of more or 

 less acid resulting from the decay of the relatively large quan- 

 tity of organic matter would tend to neutralize the lime and 

 make conditions less favorable to scab. 



