Optimizing an Organic Method of Sugar Beet Cultivation and Yield Gap Decrease in Northern Poland

In the period of 2016–2018, two series of field studies on organic sugar beet growing ( Beta vulgaris L.) were carried out in northern Poland on Luvisol loamy soil (medium–heavy) soil in Bałcyny and Płonne. The aim of this study was to decrease the yield gap between organic and conventional beets. Factors to increase the yield of organic beet were differentiated fertilization (cattle farmyard manure (FYM), compost, and Bioilsa) and choice of varieties (Eliska, Jampol, and Sobieski). The reference point was the conventional cultivation of the same sugar beet varieties, fertilized with manure and NPK mineral fertilizers, the prevailing standard of sugar beet cultivation in Poland. High sugar beet root yields exceeding the average yield in Poland by 25–30% were obtained in both studies, both in conventional and organic cultivation. Higher root and white sugar yields were obtained in the study conducted at Płonne (with similar soil conditions to those at Bałcyny), but they were characterized by higher temperatures during the growing season. The lowest root yields in both experiments were obtained by fertilizing the organic beet with compost (66.1 t per ha in Bałcyny and 78.13 t per ha in Płonne), which were 10.8% and 8.5% lower than the conventional crop, respectively. Higher root yields in organic cultivation were obtained by fertilizing the sugar beet with FYM, which reduced the differences from conventional beet to 7.7% in the study in Bałcyny and 2.1% in the study in Płonne. Thus, the results showed no need to convert cattle FYM to compost. The highest root yields in organic cultivation were obtained by fertilizing the sugar beet with Bioilsa N 12.5 supplemented with mineral fertilization of K, Mg, and S (Patentkali). This fertilization provided a yield of 78.1 t of roots per ha in Bałcyny, which is a reduction in the yield gap to 1.4%, a statistically insignificant value. Moreover, in the study at Płonne, organic sugar beet fertilized with Bioilsa and Patentkali yielded 86.7 t of roots per ha, compared to 85.6 t per ha of conventional beet, so a yield gap was not seen here. The choice of varieties was also of great importance for root and pure sugar yields in both farming systems. The lowest yields were obtained from the Eliska variety, and at Bałcyny, a change of beet cultivar to Jampol increased the organic root yield from 68.8 t per ha to 76.0 t per ha, while reducing the yield gap from 10.1% to 2.2%. At Płonne, replacing the Eliska variety with Jampol reduced the yield gap between organic and conventional roots from 6.6% to 0.3%.