20 Experiment Station Bulletin 367 



those under any other treatment. Since the basic fertilizer of all other 

 treatments included chloride, it would seem that the chlorine content of 

 the fertilizer depresses the starch content of the tubers. This theory is 

 substantiated by greenhouse trials. 



The Green Mountain variety was grown in the field tests in 1945. 

 Due to a severe outbreak of aphids, and in spite of the use of DDT dur- 

 ing the season in which the aphids were active, there was a great deal of 

 late season spread of leaf roll with subsequent development of net necro- 

 sis. 



It was thought that the use of sulphate of potash, or one of the rare 

 elements applied, might possibly reduce the amount of net necrosis in the 

 crop. Such was not the case, however, since an examination of approxi- 

 mately 500 tubers from each treatment showed no significant differences 

 for the various treatments. 



Experiments were carried out during the 1945 season with different 

 methods of applying fertilizer. In one test, all of the fertilizer was ap- 

 plied with the planter and contrasted with plowing all of it under. In 

 another series of plots, half of the fertilizer was applied with the planter 

 and half was plowed under. For those plots on which all of the fertilizer 

 was applied with the planter, the yield was slightly better than when part 

 or all of the fertilizer was plowed under. Yield differences were slight, 

 however, and since total yields in all cases were small, it is doubtful if the 

 differences, which amounted to about 12 bushels per acre are significant. 



The effect of fertilization upon quality of Green Mountain potatoes 

 were tested in field plots at Northwood Ridge. The fertilizer variations 

 involved deviations from a normal 5-10-10 fertilizer, and included omis- 

 sion of P and K from the formula, doubling of the P or K content of the 

 formula, the omission of chloride from the formula, and the addition of 

 Ca and S in the form of gypsum. 



These field trials showed that tubers from the low chloride or no 

 chloride treatments had a higher quality rating than those from the treat- 

 ments which contained chloride. The average quality ratings were re- 

 spectively 94.4 and 88.5 for the two groups, or a difference of approxi- 

 mately 1.18 per cent starch in favor of the low or no chlorine treatments. 

 Extra phosphorus to give a 5-20-10 formula whether added as 20 per cent 

 superphosphate or as 43.8 per cent superphosphate tended to increase the 

 quality rating. Extra potash to give a 5-10-10 formula increased the qual- 

 ity rating from 92.2 to 95.9 when K0SO4 was used, but decreased the 

 quality rating from 88.4 to 85.1 when KCL was used. 



Greenhouse experiments involving a study of the influence of cal- 

 cium, sulphur and chlorine upon the yield and quality of Green Mountain 

 potatoes showed that an adequate supply of calcium and sulphur were 

 essential to good yields and good quality, whereas chloride had a slightly 

 adverse effect on yield of tubers, and a strongly adverse effect on the 

 quality rating of the tubers, but a slightly stimulating effect on the growth 

 of tops. 



F. S. Prince, P. T. Blood, L. T. Kardos 



