1998 Volume 36 Issue 3 Pages 151-157
To establish a year-round hydroponic method and a highly productive cultivation technique of paddy rice, we performed three cultivation tests in 1) completely controlled facility equipped with high pressure sodium lamps (HPS) and metal halide lamps (MH), 2) a facility with HPS using together with sunlight, 3) a facility with HPS and MH together with sunlight, 4) a facility with MH lamps together with sunlight and 5) a facility with only sunlight in 1994 and 1995. Photosynthetic photon flux density (PPFD) was greater in the completely-controlled facility with supplemental lighting, facility with HPS, facility with MH and HPS, facility with MH, and facility with only sunlight, in these order. The PPFD had significant positive correlations with the number of panicles, panicle length, number of grains and weight of brown rice, and had a negative correlation with the percentage of abortive kernels. When incorporated in the first stage of the multiple regression equation by a stepwise method that determined the brown rice weight, the contribution of PPFD was 96%. Particularly in the completely controlled facility and the facility equipped with MH and HPS, the increased photosynthesis brought about better growth and yield. Though the overall mean illuminance during rice growth also had a positive correlation with the weight of brown rice, its contribution by the multiple regression method was markedly low.
