Effect of Seeding Time and Phosphate Fertilizer Using the Method of Local Application below the Seeds on Yield in Direct-sown Seeds of Onions (Allium cepa L.) in Central Japan

Abstract

We investigated the effect of different seeding dates on direct sowing with or without phosphate fertilizer applied locally below the seeds of the onion variety ‘Tarzan’ in a temperate zone. The number of leaves was analyzed, and a significant correlation was found between the number of leaves at the beginning of foliage fall-over and yield. Therefore, in direct-sown cultivation, in order to obtain a stable yield equivalent to transplanting, it is necessary to have the same number of leaves at the beginning of the foliage fall-over stage as when using the transplant method. In addition, using regression analysis, a significant correlation was observed between the number of leaves and effective cumulative temperature. The results suggest that it is necessary to sow seeds in late September when using the direct sowing method to obtain yields equivalent to the transplant method in a temperate zone, but pest control and nitrogen supplementation must be performed in a precise and timely manner. In addition, the effects of locally applying phosphate fertilizer below the seeds were found to have little impact on yields of onion in brown lowland soil.