Onion set cultivation as a system for overcoming yield reduction by the unstable climate during the establishment period

The abnormal weather patterns due to global warming worldwide are seriously affecting agricultural production. Unstable climate during the planting period affected onion (Allium cepa L.) yield in Hokkaido, where the production shares more than 60% in Japan. In the Hokkaido production regions, onion seedlings are usually planted from late April to early May and onion bulbs are harvested from late August to mid-September. Before planting seedlings, the soil is tilled by a vertical harrow and up-cut rotary to crush finely for a smooth mechanical planting. The variation in onion yield was recorded in the recent 16 years with a coefficient of the variation of 18% in Iwamizawa area, one of the production areas in Hokkaido. Continuous rainfall from late April to mid-May led to the delay of planting operation because field machinery could not operate in wet soil, causing a delay of early growth and yield reduction in 2009, 2011 and 2013. Conversely, seedling growth was suppressed by low rainfall in 2014. Set cultivation, a planting system of small bulbs instead of seedling, began to be examined for obtaining standard yield even in unstable climate. This study evaluated the effect of soil moisture on onion ('Kitamomiji 2000') growth using two types of onion establishment methods, seedlings and sets. Both onion types were cultivated in Wagner pots with 3 ranges of soil moisture based on pF values, 1.6, 2.0 and 2.4. Onion plants emerged from sets had a higher number of expanded leaves and leaf length and increased bulb weight in every pF value as compared to seedlings. However, their leaf growth in dry soil (pF 2.4) was smaller than those in the soil with pF 2.0 and 1.6 in set cultivation. Set is an alternative nursery for the establishment of early growth in onion.