2018 Volume 17 Issue 4 Pages 405-413
The effect of nitrogen and potassium fertilization conditions combined with the local application (2–4 cm below the seeds) of calcium superphosphate on the bulb yield of direct-seeded onions (Allium cepa L.) was investigated. In addition, to clarify the effect of fertilization on the number of leaves during the growing period and the relationship with the number of leaves and yield, we investigated growth traits such as the early growth stage plant height and nutrient absorption in the bulb initiation stage, which may affect the number of leaves. Although the mechanism by which a fertilizer component applied before sowing, with the local application of calcium superphosphate, contributes to yield is still not completely understood, the results show that nitrogen and potassium application prior to the second leaf stage increases phosphate absorption and promotes nitrogen absorption in the bulb initiation stage. In addition, it leads to an increase in the number of leaves at the fall-over stage and the bulb weight per leaf. Moreover, this study shows that only applying calcium superphosphate locally does not increase the yield of ‘Okhotsk 222’, but that it requires combination with nitrogen and potassium application within the plow layer prior to the second leaf stage. This process promotes the absorption of nitrogen and phosphoric acid at the bulb initiation stage and contributes to an increase in bulb yield.
