Influence of Rainfall Pattern on Effect of Nitrogen and Potassium Topdressing in Combination with Local Application of Nitrogen and Potassium at the Timing of Sowing on the Growth and Yield of Direct-seeded Onions (Allium cepa L.)

Abstract

Direct seeding of onions leads to increased susceptiblity to meteorological conditions because it results in a longer growing period of about two weeks than transplant cultivation. Therefore, we investigated the effect of the combination of local fertilization consisting of nitrogen, phosphoric acid, and potassium, and a top-dressing of nitrogen and potassium on the growth and yield of directly sown onions in Tokachi, Hokkaido. In addition, the effect of the difference in soil moisture due to rainfall on growth and yield with the above fertilization methods during the experimental year was investigated. The results differed depending on the year of the experiment, and it was shown that the difference in top-dressing of nitrogen and potassium on the growth was affected by the amount of precipitation. Consequently, we inferred that the difference in fertilization method did not lead to an increase in the weight of bulbs due to the difference in nutrient uptake during each experimental year. Our results suggest that if rainfall occurs after the top-dressing application in the middle of June and the onions absorb the fertilizer component, the weight of bulbs would increase.