The Effect of Non-Woven Fabric Floating Row Covers on the Emergence, Growth, and Bulb Yield of Direct-seeded Onions (Allium cepa L.) in a Subarctic Area

抄録

The effect of non-woven fabric floating row covers on the growth and yield of spring-sown, direct-seeded onions was investigated in Hokkaido, a subarctic island of Japan. Field experiments were carried out in 2014, 2015, and 2017. The seeds were sown in late April in each year. Floating row covers were installed a few days after seeding and kept in place until the end of May. During the treatment period, average daily maximum and minimum soil temperatures were approximately 4–5°C and 1–3°C higher, respectively, under covered compared with uncovered treatment. The effect of row covers on soil moisture varied annually. Emergence was obviously accelerated by floating row covers, as evidenced by an emergence date that was 1 to 4 days earlier than that of the uncovered treatment. Growth during early stages was promoted by floating row covers; however, the difference in plant growth between covered and uncovered treatments gradually decreased, with an almost non-significant difference observed by the beginning of bulb formation. The effect on growth earliness differed between years and an earlier lodging time was observed in 2015, in which the sunshine duration during the covered period of about 40 days reached 350 hours and the soil temperature difference between covered and uncovered treatments was larger than the other 2 years. Floating row covers had little effect on bulb yield. As for other growth aspects, decreased survival under floating row covers due to heat injury was observed when high temperature and drought simultaneously occurred. Floating row covers also tended to decrease onion maggot feeding damage. Non-woven fabric floating row covers effectively promote the emergence and early growth of spring-sown, direct-seeded onions mainly by elevating soil temperature. Although the degree differs depending on the year, earlier bulb formation and lodging, and a decrease in onion maggot feeding damage are also expected. These results suggest that non-woven fabric floating row covers may be a viable option to reduce the risks of delay in emergence, growth suppression caused by low temperatures, delay in lodging time and feeding damage due to onion maggot.