Control of withering and yellowing of winter onions in spring

Recently, the author has been receiving letters or calls from the masses to inquire about the management of winter onions in spring. Some people talk about winter onions that grow well under low temperature conditions. After the temperature rises in the beginning of spring, there appears the phenomenon of yellowing leaves, aging roots and even withering. Cold-tolerant winter onions seedlings are not as good as local winter onions. Why?

Through field observation, the author learned that a similar situation occurred in winter onions in most parts of the country in the spring of 2005. In Jiaodong Peninsula, which has the largest planting area in China, a large number of onion seedlings have died due to improper management. The reason is mainly caused by the abnormal weather in which the temperature fluctuated in the spring of the Winter Solstice in 2004 and 2005. In the early winter of 2004, the temperature was higher all over the country, and the spring onions grew very well. Before and after the Spring Festival in 2005, the weather continued to be cold, and the lowest temperature appeared in Zhengzhou in more than a decade. The leaves of common onions have turned yellow and dry, while winter onions are still firm and dark green, showing superior low temperature tolerance. At the same time, due to the low ground temperature, the root growth rate of winter onions is slower, and the occurrence of new roots is less. Due to the slow growth of the aboveground parts, the aboveground and underground parts can basically grow harmoniously. After the beginning of spring, the temperature went up and down, and in February, the highest temperature in Zhengzhou reached more than 20 degrees Celsius. The sudden rise in temperature made the aboveground part of winter onions grow rapidly, the transpiration was exuberant, and the plants needed a lot of water and inorganic salts. But in the same period, the ground temperature increased slowly, the root activity was not exuberant, and the new roots germinated less, which could not supply sufficient water for the aboveground parts in time. There is a contradiction between the growth of the aboveground and underground parts, which leads to the phenomenon of withered leaves and aging roots, and in serious cases, the roots wither and the leaves die. However, because the leaves of common scallions or green onions are small and small, the sudden rise of air temperature has little effect on the leaf growth and transpiration of common onions or scallions. With the increase of air temperature and ground temperature, the plants gradually turn green, and the growth condition is better than that of winter onions. Experienced people should do a good job in the management of winter onions in spring, that is, early planting, early watering, and early ploughing, and the growth of well-managed winter onions is obviously better than that of ordinary green onions. If the plant cell division agent is added in the watering process, spraying Jianzhibao when the temperature is high, better results will be achieved. People in some areas are managed by transplanting small arch sheds or covered with plastic film before winter, and winter onions are also growing well.