Effect on the Phosphorous Uptake, Early Growth, and Yield of Direct Seed Onions (Allium cepa L.) in Andosols When Local Fertilization with Calcium Superphosphate is Applied below the Seeds

Abstract

In this study, we investigated the effect of local fertilization with calcium superphosphate applied 2–4 cm below the seeds on the phosphorous uptake, early growth, and yield of direct seeded onions (Allium cepa L.) in andosols. In andosol fields, where available phosphate was measured by the Truog method to be less than 10 mg・100 g^-1 dry soil, local fertilization accelerated the emergence of the second or third leaf and was shown to promote growth. This could be seen through the increased number of developing leaves throughout the growing season, which led to a greater plant height and dry weight. Furthermore, in a trial comparing broadcast with local fertilization, the latter yielded more bulbs greater than 8 cm in diameter at harvest than the former. We concluded that local fertilization with calcium superphosphate 2–4 cm below the seeds improved early growth and the final yield of direct seeded onions compared with broadcast fertilization.