抄録
To obtain basic information about introducing crops to a rooftop that receives little sunshine, growth and development of rice was investigated under semi-shaded and sunny conditions on a flat roof in 2007 and 2008. Paddy rice cultivars Nipponbare, Nakateshinsenbon, and Takanari were analyzed in this study, and some other cultivars were also planted in containers. Two types of soil were used, namely paddy soil and mixed soil, including “Acre” recycled soil originating from a water purification plant (Arakida : sand : Acre=7.0 : 1.5 : 1.5). Semi-shade was provided by two metal screens located on the east and west sides of a container. Daily solar radiation in the semi-shaded plot was approximately 50% of that in the sunny plot. The number of panicles per hill in the semi-shaded plot was 34-98% less than in the sunny plot. Tiller number was highest (65-98%) for Nakateshinsenbon, suggesting that this cultivar might be suitable for cultivation under semi-shaded conditions. In sunny and semi-shaded plots, the number of tillers on the 35th day after planting decreased curvilinearly with the decrease in accumulated solar radiation between the 1st and 30th day after planting. The percentage of ripened grains tended to decrease with reduced solar radiation (averaged over 10 days from the 15th day after full heading date) and with increment in the number of spikelets per plant. Grain yield in the semi-shaded plot compared to the sunny plot was 29% (paddy soil) and 38% (mixed soil) for Nipponbare, and 41% and 57%, respectively, for Nakateshinsenbon. Not a large differences in growth and development of Nakateshinsenbon were observed between paddy soil and mixed soil. Our results suggest that when rice is introduced to a rooftop garden under semi-shaded conditions, it should be planted considering planting density to promote tillering, and cultivars should be chosen that can adapt to mixed soil, including recycled soil.
