Field studies were conducted in 2011 and 2017 in Nara and Yamaguchi prefectures in Western Japan to examine why the yield of the determinate soybean cultivar ‘Sachiyutaka’ is not improved by increasing the planting density. Branching, radiation interception (IR), radiation use efficiency (RUE), and dry matter production were evaluated in ‘Sachiyutaka’ planted at normal (<20 plants m⁻²) and high (≥30 plants m⁻²) densities. High densities were ensured by narrowing hill spaces and keeping row spaces constant. Yield and pod number at maturity were not significantly increased by increasing the planting density. The number of branching nodes and pod number were decreased by the high planting density at the Nara field site but not at the Yamaguchi site. Instead, the high planting density decreased the number of pods per node on the main stem at Yamaguchi. Although the number of nodes and pods varied with the site, pod number at maturity did not vary with the planting density at each site. The pod number may not have increased by the increase in the planting density because of the lack of dry matter production from flowering to early seed filling, probably due to the lack of IR and RUE. Thus, the lack of increase in yield in ‘Sachiyutaka’ at a high planting density may be due to the lack of change in IR, RUE, and dry matter production after flowering.

During recent years, the number of jellyfish in the waters surrounding Japan has been increasing tremendously. Not only does this have a negative impact on the environment, but it is causing serious damage to the fisheries and coastal facilities. Jellyfish chips, i.e., desalted, dried, and shredded jellyfish, can act not only as an effective organic fertilizer, but also as a bioherbicide in paddy fields. However, we observed that following the application of jellyfish chips, the rice yield decreased by approximately 10% compared with that of conventional rice cultivation, and that weed control was insufficient and unstable. To overcome these limitations, we applied rice bran together with jellyfish chips, and compared the rice yield with that achieved by the conventional cultivation practice. The combined application of jellyfish chips and rice bran successfully controlled the weeds in the paddy fields providing a grain yield similar to that of conventional rice cultivation. The improvement in yield might be due to the difference in organic fertilizer composition and the onset time of fertilizer effect. Furthermore, the improvement in herbicidal effect can be attributed to the synergistic effect of different growth suppressing substances in the two organic fertilizers. Overall, the combined use of jellyfish chips and rice bran might be an innovative organic practice in paddy cultivation.

Rice cultivars ‘Tachiayaka’ and ‘Tachisuzuka’, which have short panicles, were developed for whole-crop silage use because of their improved feed value owing to their decreased numbers of hard-to-digest spikelets. However, these cultivars do not produce a sufficient number of seeds for propagation. Nitrogen application at the panicle-formation stage, low planting density and late transplantation improve the unhulled rice yield in ‘Tachisuzuka’, and similar nitrogen application also improve seed production in ‘Tachiayaka’. However, changes in cultivation methods other than fertilization have not been investigated in ‘Tachiayaka’. Therefore, the effects of the planting density on the yield components of ‘Tachiayaka’ were studied from 2014 to 2016. With an increase in planting density, the panicle number increased; however, the number of spikelets per panicle decreased. Thus, the spikelet number per unit area was not significantly affected by the planting density. In addition, there were more late-emerging panicles in 5.6 hills m^–2 or 7.4 hills m^–2 than in 11.1 hills m^–2, indicating that an extreme low density is unsuitable.

Poor seedling establishment is a major problem for Early-Winter Direct-Sowing cultivation in rice. We examined the effects of seed coating with three materials (iron, calcium peroxide, starch) on the seedling establishment. The seedling establishment rate was only 1～3% in the control without seed coating in both 2016/2017 and 2017/2018 seasons in Iwate Prefecture. Only the coating with iron showed a significant increase in the seedling establishment rate, that is, 24% in the 2016/2017 season and 11～30% in the 2017/2018 season. Significant improvement of seedling establishment by seed coating with iron was confirmed similarly in additional four Prefectures (Hokkaido, Aomori, Akita and Mie) in 2017/2018 season. We concluded that the seed coating with iron is a promising methodology for improving seedling establishment for Early-Winter Direct-Sowing cultivation in rice.

In order to obtain fundamental information on petiole elongation for improving soybean plant type, the petiole elongation on the main stem was continuously observed in detail using pot-grown plants. The determinate growth type Fukuyutaka was used in this experiment. The elongation of petiole on the main stem was slow at the early phase, rapid during the mid-phase and again at the late phase. Concerning the final length of petiole on the main stem, the first trifoliolate leaf was the shortest and longer at upper position, while uppermost 2nd or 3rd petiole was the longest of the petioles. This pattern was similar to the final internode length on the main stem. A positive correlation was found between the Nth petiole length and the (N-1)th internode length in the same phytomer. This relationship suggests that the effects of various factors on the petioles would be similar to those on the internodes. When the Nth leaf emerged, the (N-2)th petiole elongated the most rapidly, the (N-6)th or (N-5)th petiole stopped elongation. The late phase of petiole elongation was considered to be more susceptible to the effects of environmental stress than that of internode elongation. These results would be useful for controlling soybean petiole elongation to improve the plant type.

Bioethanol is a promising alternative to fossil fuels and a potential countermeasure to global warming. Erianthus, a perennial C₄ grass, may be a useful raw material for cellulosic bioethanol, mainly because of its high biomass production potential. Little is known about the developmental morphology of the panicle in Erianthus. In this study the fundamental structure and development of panicle in Erianthus were examined. The inflorescence (panicle) of Erianthus is a raceme with conical appearance. The rachis of the panicle has the first, second and third order rachis branches. The spikelets are formed on every order rachis branch. A pedicellate spikelet and a sessile spiketet are usually formed in pairs, while only a petiolate spikelet is formed at the tip of the rachis and each order rachis branch. Each spikelet has one floret covered by a pair of glumes and the floret consists of a lemma, a palea and floral organs, namely two lodicules, three stamens and a pistil. The developmental process of panicle formation excluding the vegetative stage was classified into five stages: formation of bract primordia (Stage 1), formation of primary rachis branches (Stage 2), formation of high order rachis branches (Stage 3). formation of spikelets (Stage 4) and formation of florets (Stagee 5). These developmental stages proceeded acropetally and not simultaneously. The developmental morphology of panicle obtained in this study should be useful to understand tiller formation with reference to canopy development.