Marketable Yield and Grade Distribution of Sweetpotato (Ipomoea batatas Lam.) as Influenced by Production System and Season in a Temperate Climate
Protected culture systems offer a practical strategy for extending sweetpotato (Ipomoea batatas [L.] Lam.) production into temperate regions where cool soil temperatures and limited growing degree days (GDD) constrain storage root development. This study evaluated sweetpotato yield performance under four production systems (black plastic mulch [BPM], bare soil [BS], low tunnel [LT], and high tunnel [HT]) across two growing seasons (2022 and 2023) at Rock Springs, PA. Ten commercial cultivars were grown in a factorial randomized complete block design with four replications. Total yield (TY), marketable yield (MY), and individual grade yields (U.S. No. 1, Petite, Jumbo, Canner, and Cull) were assessed, along with seasonal soil temperatures (2023 only) and cumulative GDD (base 15.5 C). Year, Treatment, and their interaction were significant sources of variation for most yield components. In 2022, HT recorded the highest TY (21.1 Mg/ha), and BS the highest MY (16.8 Mg/ha), while LT produced the lowest values for both metrics. In 2023, BPM led all treatments in both TY (26.8 Mg/ha) and MY (26.6 Mg/ha). No single system consistently dominated across years, reflecting the importance of seasonal weather conditions on treatment response. Seasonal average soil temperatures in 2023 ranged from 20.7 C (BS) to 22.7 C (HT) but were not significantly correlated with grade yield at alpha= 0.05 (n = 4). Cumulative GDD ranged from 493 to 651 across treatments and years, well below the thresholds typical of major production regions. BPM provided the most consistent agronomic performance, supported by moisture conservation and weed suppression benefits that extended beyond the modest soil temperature advantage over bare soil. These results indicate that protected culture, particularly BPM, can support commercially viable sweetpotato production in temperate Pennsylvania, and that cultivar selection tailored to the production system is critical for optimizing yield and grade distribution.