Productivity of the warm-climate crop sweet potato (Ipomoea batatas L.) in northern latitudes

Sweet potato ( Ipomoea batatas (L.) Lam.) has a potential to become a new field crop for higher latitudes. Sweet potato was cultivated for the first time in the fields of Estonia. During the study, the photosynthetic characteristics and yields of sweet potato cultivars ‘Evangeline’ and ‘Covington’ were investigated under fertilisation with two nitrogen (N) rates (0 and 100 kg ha −1 N) and various fertilisers in 2018, 2019 and 2021. Variation in fertiliser rate and composition had no effect on CO 2 assimilation rate ( A ) and stomatal conductance ( g s ). The negative relationship between photosynthetic nitrogen use efficiency (PNUE) and intrinsic water-use efficiency (iWUE) among cultivars and treatments indicated that water availability could limit nutrient availability and ultimately reduce the potential yield in northern growing regions. The highest sweet potato tuber yield (t ha −1 ) was obtained from ‘Evangeline’ and ‘Covington’ at N0 in 2021. A comparison of yields of 2018 and 2021 experiments suggests that sweet potatoes can be grown in high latitudes. It can be concluded that depending on weather conditions, cultivars and soil properties, fertilisers can promote high plant productivity. Further studies should focus on sweet potato plants traits that enable the efficient use of nutrients and water during a short and potentially dry growing season.