Cassava (Manihot esculenta Crantz) is highly productive in the tropics and sub-tropics, including marginal conditions. A high starch content cultivar IAC-576-70, selected at the Instituto Agronômico de Campinas, São Paulo, Brazil, was grown in a field in Kagoshima Prefecture during cropping seasons from 2007 to 2009, to determine its capability as a biomass source even in a temperate region of southwest Japan. At the experimental site, the annual mean temperature was 18.3°C with several incidences of frost in winter and annual mean rainfall of 2280 mm (for years from 1971 to 2000). Under these conditions, cassava grew for 8 months from late April to mid-December, and produced a total dry weight of 1793 g m^–2, tuberous root dry yield of 524 g m^–2 and tuberous root fresh yield of 2000 g m^–2. The yield in Kagoshima was equivalent to that at 8 months after planting in tropical regions.

In order to obtain basic knowledge for constructing a prediction model of direct-seeding cultivation on well-drained paddy field, we compared developmental stages for direct-seeding and transplanting among eight cultivars differing in maturity type from very early to mid-late including newly bred ones by the cropping season test in Tsukuba-Mirai City. Although accumulated temperature from direct-seeding or transplanting to ripening tended to decrease the later the planting date in both methods, the effect was large for mid-late maturing cultivars and small for very early maturing cultivars. The temperature in direct-seeding cultivation was higher and with larger year-to-year variability than in transplanting cultivation. This was considered to reflect the temperature during the raising of seedling period and the cultivation was easily affected by environmental factors in the early developmental stage. In the ripening stage, the difference in accumulated temperature with different planting dates was small in plants headed together, while the effects of weather factors, such as rain, and temperature drop, were large in both methods. Introduction of heading data into an existing heading date prediction model of transplanting cultivation revealed a significant correlation between the observed date and the estimated date. By improving the existing prediction model, it may be possible to estimate and predict the heading dates for direct-seeding cultivation. The findings help provide basic knowledge for constructing a prediction model and support introduction of direct-seeding cultivation to the current cultivation system.

The variable-rate fertilization (VRF) based on a diagnosis of crop growth would be effective for the enhancement of yield and quality of wheat. In this study, we hypothesized that control of the tiller number would be important for VRF in wheat grown through intensive nitrogen fertilization during stem elongation (INFDSE) and determined whether yield losses due to poor seedling establishment could be compensated by control of the amount of N top-dressed at tillering (GS14). The poor seedling establishment was reproduced by lowering the sowing density. At the lower sowing density, seedling density was approximately 80 stands per m² which was significantly lower than that at the normal sowing density which had approximately 120 stands per m². In GS14, the tiller number at the lower sowing density was also lower than that at the normal sowing density. Increase in the amount of N top-dressed at tillering, however, did not increase the tiller number; the tiller number at the initiation of stem elongation was approximately 400 per m² in all treatments. Even in plants grown by INFDSE, a ear number of more than 350 per m² could be obtained at the lower sowing density because more than 85% of the tillers formed an ear. As a result, yields of plants grown at the lower sowing density were identical to those of plants grown at the normal sowing density under INFDSE. This study confirmed that under INFDSE, although the tiller number could not be controlled by N top-dressing at tillering, a high yield can be derived at seedling density of more than 80 per m².

We examined the relationships between nitrogen topdressing at flowering and grain ash content in the wheat variety “Yukichikara” for bread in a sand dune and upland field converted from paddy field of Niigata prefecture. In the sand dune, the grain ash content and phosphorus concentration were increased by nitrogen topdressing at flowering. In the upland field converted from paddy field, nitrogen topdressing at flowering did not affect grain ash content. This difference in these fields depended on the relationship between increment of grain phosphorus content per unit area and grain yield. The phosphorus uptake during the ripening period was increased by nitrogen topdressing at flowering, and the increment was greater in the sand dune than in the upland field converted from paddy field. Available phosphoric acid concentration (Truog P) was greater in the sand dune than in the upland field converted from paddy field, and a possible effect of the available phosphoric acid concentration on phosphorus uptake during ripening period was implied. These results suggest that the relationship between nitrogen topdressing at flowering and grain phosphorous concentration depends on the balance between increment of grain phosphorus content per unit area and that of grain yield. Additionally, it was implied that grain phosphorus concentration and grain ash content were increased by nitrogen topdressing at flowering in soil with high available phosphoric acid concentration.

To elucidate the factors that affect seed yield of rice cultivars with a short-panicle (SP) caused by a mutation in the SP1 gene, we grew 64 SP cultivars in paddy fields in 2015 to 2018 and transplanted 4 SP cultivars (‘Chugokushi224’, ‘Chugokushi225’, ‘Tsukisuzuka’ and ‘Tsukikotoka’) on 3 dates in 2018 in paddy fields at the Western Region Agricultural Research Center. We recorded days to heading (DTH), dry weight per panicle, panicle number and panicle dry weight per m². Dry weight per panicle contributed to panicle dry weight per m², but panicle number did not. Dry weight per panicle had strong negative correlations with DTH in all SP cultivars and in all transplanting dates when DTH, 80: dry weight per panicle increased with shorter DTH.

Erianthus, a perennial C₄ grass, is a raw material for cellulosic bioethanol, mainly because it has high potential for biomass production based on its large canopy. In this study, the mechanical strength of the leaf blade was examined with reference to its morphology. The results showed that the weight and mechanical strength of leaf blade increased basipetally along the leaf axis. The potential weight of the blade to support itself, estimated from the mechanical strength measured with a force-gauge, was not less than the actual leaf weight. These results are in agreement with the actual conditions of the canopy, and suggest the validity of our methodology. Measurement of the mechanical strength of only the midrib itself indicated that the mechanical strength of the whole leaf blade was mainly based on the development of the midrib which was larger and had changed from circular to U-shaped basipetally along the leaf axis excluding the leaf tip with undeveloped midrib. These results suggested that the size and shape of the midrib contribute to the mechanical strength to support the leaf blade.

The Japanese rice variety “Shinrei” from the Kyushu region was subjected to short-day (9-h daylength) and long-day (14-h daylength) treatment in a phytotron with a day/night temperature regime of 30/22°C. Under the long-day and short-day conditions, the heading time was 85 days and 60 days, respectively; and, the percentage of sterility was 3% and 28%, respectively. Under the short-day condition, the anther was bent and was about 1.2 mm in length, while under the long-day condition the anther was about 1.7 mm in length. An increase in sterility was observed when the anther was shorter than about 1.5 mm and the number of pollen grains per anther was less than about 600. The anther length was affected by day-length from 3 to 9 days after panicle initiation as well as by days to panicle initiation. Short-day treatment during this period decreased the panicle length and number of pollen grains per anther, resulting in an increase in the percentage of sterility.

Major factors that decrease soybean yields in Japan include excessive soil moisture and drought stress. In the present study, a WI (Wet Index) was developed using soil moisture estimates based on the FAO56 model to evaluate both risks of soil dryness and wetness. In addition, to assess the risk of wet losses, the days when ratio of WI was equal to one (RWI), which implied that soil moisture content reached a maximum, was adopted for every growth stage. When the relationship between WI or RWI and yield was evaluated using a partial correlation coefficient, WI had a positive correlation with emergence period approximately 30–40 days after emergence, seed filling phase, and maturity phase, and RWI had a negative correlation with emergence period approximately 20–30 days after emergence and approximately one week before flowering period. We evaluated moisture and drought stress risks, which present challenges in farmers’ fields, and revealed the growing stages at which moisture and drought pose the highest risks. The results could offer critical insights for the estimation of dryness and wetness losses in the field.

In recent years, the area of direct-seeded rice cultivation has been increasing, but the occurrence of volunteer rice has disturbed the spread of direct-seeded cultivation. Influence of multiple factors of combined cultural (existence of false seedbed, seeding methods, etc.) and chemical control on the transition of emerged and number of surviving plants was investigated to establish a system to control volunteer rice. Almost all “Tachisuzuka” and “Hinohikari” tested as volunteer rice emerged during the dry season. “Tachisuzuka” germinated slightly slowly, but the cumulative emergence rate of both species reached approximately 100% in early June. In 2017, the number of surviving volunteer rice in all treatments was significantly lower compared with the conventional dry direct-seeded cultivation practice. However, there was no significant difference among the seeding methods (full, partial, no plowing). Similarly, the effect of the mortality rate with high-concentration bispyribac-sodium application, which was expected to inhibit growth of rice seedlings, was low. In 2018, we examined the effects of soil compaction after seeding and preparation of false seedbeds; however, there was no significant difference in the number of surviving volunteer rice between treatments. The results of the two year study revealed that delayed seeding contributed to the reduction in the number of surviving volunteer rice more than false seedbed and bispyribac-sodium application.

In this study, we clarified the effects of low density seedling establishment in broadcast cultivation, which is a labor saving technique, on the growth, yield, and seed quality of soybean. In broadcast cultivation, the seedling establishment in the four corners of the plot (low density plot, LD) was about 35% of that further in the plot (average density plot, AD). In LD, the shoot dry weight was lower than that in AD until the flowering stage. Thereafter, the shoot dry weight of the soybean in LD increased with a sharp increase in leaf-area-index (LAI), and became similar to that of soybean in AD at the seed-filling stage. Although, the density of nodes (number of pods per m²) was lower in LD than in AD, the number of branches, number of branching nodes per plant, and number of pods per node were higher. Therefore, there were no significant differences between LD and AD in number of pods per m² and yield. There was a positive correlation between the number of pods per node and increments in the values of LAI and SPAD-meter readings from the flowering stage through to the seed-filling stage. These results suggest that in broadcast cultivation the growth of branches in LD was promoted and the number of pods per node was increased due to vigorous leaf expansion, accompanied with leaf-color improvement from the flowering stage to the seed-filling stage.