POTASSIUM RATE AND SOURCE EFFECTS ON POTATO YIELD, QUALITY, AND DISEASE INTERACTION

Field experiments were conducted over eleven site-years where five K r ates (0, 93, 187, 280, and 373 kg K ha(-1)) as KCl or K2SO4 were band- applied at planting to potato (Solanum tuberosum L.). Significant yiel d increases up to 332 kg K ha(-1) were observed in five of eleven site -years when soil test K ranged from 75 to 110 mg kg(-1). The increase in tuber yield was associated with an increase of tuber size (170 to 3 70 g) and above in the US#1A category. Lack of yield response at the o ther site-years may be due to the high soil test K (125 to 180 mg kg(- 1)). Statistically significant differences in total tuber yield were n ot evident between the two sources of K fertilizer studied; however, t here was a tendency for a significant rate x source interaction (p < 0 .15) in five site-years where K2SO4 increased tuber yield more than KC l at rates up to 280 kg K ha(-1). Above this rate, tuber yield decreas ed for K2SO4 but remained stable for KCl. Based on the tuber yield dat a and initial soil test It from the controls of each site-year, data f rom this study suggest that 104 mg K kg(-1) is a critical pre-plant so il test level. A reduction in specific gravity with increasing applied K was evident in most of the site-years of this study, although decre ases were generally not as marked when K2SO4 was used. A significant d ecrease in hollow heart with increasing rate of K fertilization was ob served in four of eleven site-years; however, statistically significan t yield responses to added K were found at only one of these sites. Th e incidence of Rhizoctonia solani was generally not affected by It rat e; however, there was a tendency in some site-years for a higher disea se incidence when KCl was used instead of K2SO4. Potassium rate slight ly decreased stem numbers per seed piece, averaging 3.7, 3.6, 3.5, 3.4 , and 3.3 across all experiments, for the 0, 93, 187, 280, and. 373 kg K ha(-1) rates, respectively.