Effects of high-temperature and soil moisture conditions on the physiological response of onion

The objectives of this study were to determine the effects of a combination of high-temperature and excessive irrigation treatments on growth, physiological response, and yield of onion (Allium cepa). These experiments were conducted in a typical plastic house (one side open and the other side installed ventilation fans) with a gradient air temperature (maximum different value of air temperature: 6°C). The excessive irrigation (EI) treatment commenced at 149 days after transplanting. Significant differences were found in the growth parameters in response to air temperature and soil moisture conditions. Under a combination of ambient (A) + 6°C and A + 3°C with optimal irrigation (OI) conditions, the plant height was 128.7 and 128.9 cm/plant, respectively, which was the highest among all the tested treatments. The number of leaves showed the greatest difference of 11.8 and 11.7/plant at A + 3°C and A + 6°C with OI and least difference of 8.6/plant in A-EI. The stem diameter and leaf width were higher under A + 3°C and A + 6°C with OI conditions than in the ambient temperature treatment. Bulb weight dramatically increased under the A + 6°C and A + 3°C temperature treatments. The marketable yields increased by 157% and 127% under A + 6°C-OI and A + 6°C-EI temperature treatments than in ambient temperature with OI. These results indicated that onion yields increased in response to 6°C or 3°C high-temperature treatments than under the ambient temperature treatment.