2017 Volume 16 Issue 4 Pages 421-434
To utilize the irrigation function of the Farm-Oriented Enhanced Aquatic System (FOEAS) in an upland field converted from a paddy field, we examined the effect of sub-irrigation at different growth stages of onion and different levels of precipitation on growth and yield of pot-cultured autumn-sown summer-harvest onion. Onion seedlings were transplanted into a large pot of andosol or gray lowland soil under rain shelter. The level of feed-water in a connected tank was automatically maintained at –30 cm from the soil surface. Plants were irrigated in each cultivation period (Early, Middle, Late, and Total periods) except for right before harvest under low-level precipitation (25% of monthly average amount of precipitation). By comparing with plants without sub-irrigation supplied with 25% of the monthly average amount of precipitation, soil water suction in sub-irrigated plots with 25% of the monthly average amount of precipitation remained low, and plant shoots grew larger. In both soils, the Total period treatment led to the largest bulb weights and diameters, and the second best was the Late plot. The increased effect of sub-irrigation on the growth in andosol was more marked than that in gray lowland soil. In the year with higher reference evapotranspiration, plants with sub-irrigation with 50 and 100% precipitation during the Total period except for right before harvest had larger bulb weights compared with those receiving 50 and 100% precipitation without sub-irrigation. In the year with a more than 10-mm higher monthly reference evapotranspiration than the average year, sub-irrigation was more effective with respect to the bulb weight and diameter. The results indicate that sub-irrigation according to the growth stage of plants and rainfall may prevent drought and increase the yield of onion.
