Article ID: SZD-041
Production and consumption of broccoli in Japan are gradually increasing; however, the country is highly dependent on imports to meet the growing demand. Large head production systems with ‘Grandome’ can decrease the reliance on imports, but their adaptability across broader areas remains unclear and it is also necessary to consider other cultivars according to regional and cultivation conditions. Therefore, in this study, ‘Grandome’ yield was evaluated from 2019 to 2021 at six autumn to spring production sites (Hyogo, Hiroshima, Kumamoto, Kanagawa, Kagawa, and Ehime). In addition to the yield evaluation of ‘Grandome’, cultivar selection tests suitable for large head production were conducted at the former three sites using 25 cultivars in Experiments 1 to 3, while the yield evaluation exclusively for ‘Grandome’ was conducted under different fertilization conditions and planting densities at the latter three sites in Exp. 4, comparing floret yield (small pieces of broccoli separated from the head). Experiments 1 to 3 revealed that ‘SK9-099’ produced high yield during the relatively warm November harvest, whereas in the subsequent December–January harvest, ‘Grandome’ and ‘Clear’ produced high yields. In years that were colder than usual during the aforementioned period and for cropping types with a harvest period from February to March through a severe cold season, late-maturing cultivars, such as ‘Tomoe’ and ‘Konbanwa’, produced high yields due to their strong low-temperature enlargement capacity. Among cropping types with a harvest period from April to May, ‘Grandome’ produced a high yield. Moreover, these cultivars could be grown in converted paddy fields. In Exp. 4, high fertilization rates and wide planting promoted head enlargement. Wide planting increased the yields under simultaneous harvesting. However, under selective harvesting, where enlarged heads were individually harvested, head size was comparable between the standard and wide planting. Therefore, wide planting had no yield-increasing effect. The optimal planting density and harvest size for maximizing yield remain unclear. Nevertheless, for the first time, this study showed that the effect of planting density on yield varied based on the harvesting method. This study achieved a floret yield of 20,000 kg per ha across all six locations in nine cultivation trials in Japan, highlighting the broad adaptability of large head production systems, particularly in the autumn to spring production areas in Japan.
