YIELD and Postharvest Quality of Tablestock Potato (Solanum tuberosum L.) in Response to Irrigation Method and Harvest Time

Increased competition for water resources has resulted in the need to evaluate more water use efficient irrigation methods. The harvest quality and storability of two tablestock potato varieties were evaluated for two spring seasons in response to irrigation method and harvest time. ‘Fabula’ and ‘Red LaSoda’ potatoes were irrigated using seepage (SP), surface drip (SD), or sub-surface drip (SSD) irrigation (tape buried 0.05 m below the seed piece). Plant vines were killed off before harvest to promote tuber skin maturation. Tubers were harvested 1 to 3 weeks after vine kill (H1, H2 and H3) and stored for 14 d at 10 ºC and 90-95% relative humidity. In ‘Fabula’, total yields for SP and SD averaged 26,230 kg.ha^-1, while SSD yields were significantly lower at 15,249 kg.ha^-1. Soil moisture fluctuations under SP resulted in higher incidences of tuber physiological disorders. At harvest, differences in tuber quality were only observed in the second season, due to prolonged exposure of tubers to wet soils. H1, SSD tubers were 8.4 N firmer than SD tubers. Increased moisture uptake resulted in decreased peel dry matter content (DMC) with increased harvest time.  SP tubers had the highest DMC at H2 and H3, compared to those grown with drip. Incomplete skin maturation in H1 tubers made them more susceptible to storage losses. H1 drip tubers were 4.9 N firmer than SP at d 0, with no significant difference by 14 d, due to moisture loss. DMC of H1, SD tubers also increased significantly, from 14.6% to 17.4% due to lower moisture content.  Ascorbic acid content (AAC) decreased with increased storage time for all H1 tubers, although drip tubers maintained a higher average of 17.1 mg/100g at 14 d, compared to SP’s 11.8 mg/100g.  In ‘Red LaSoda’, although SP produced the highest total yields in both seasons, uneven soil wetting patterns resulted in more physiological disorders. In storage, only during the second season, H1, SSD and H2, SP lost the most fresh weight of 4.1% and 3.8%, respectively, due to immature tuber skins. These results indicate that SD shows potential to improve water use efficiency in ‘Fabula’ potatoes while maintaining high tuber yields and postharvest quality. This was especially true when tubers were harvested 2 to 3 weeks after vine kill. In ‘Red LaSoda’ although SP resulted in higher yields, tubers grown with drip irrigation had comparable quality.