To improve soybean productivity, we investigated the relationships between soybean yield and growth- or field-related factors in 30 cultivated fields. First, the relationships with growth-related factors were analyzed. Under conditions of sufficient plant number, the number of branches, total number of pods per plant, and number of grains in each pod were higher and the 100-grain weight was heavier in fields with higher yield. A significant negative correlation was observed between yield and grain weight damage by stinkbugs, suggesting that timely control of these insect pests is necessary to increase the total number of pods per plant and thus increase yield. Next, with regard to field-related factors, yield was significantly correlated with ground water level, water retention time in the soil layer, and saturated hydraulic conductivity of the subsoil. To improve yield, it is therefore necessary to reduce the number of days when the groundwater level rises to less than 40 cm below the ground surface, reduce the time of water retention in the soil layer due to heavy rainfall, and to improve the physical properties of the dense subsoil. There was also a significant correlation between the number of days when the groundwater level rose to less than 40 cm below the ground surface and the water retention time of the soil layer, suggesting that the water retention time of the soil layer could be reduced by lowering the groundwater level.

Two field experiments were conducted using the sweet potato cultivar ‘Murasakimasari’ with both conventional vine planting (CVP) and tuber seedling transplanting (TST) to estimate yield properties under large ridge (LAR) cultivation with two rows in a ridge and compared with the conventional high ridge (CHR) cultivation method. The LAR shapes were LAR1 (ridge height [RH], 35 cm; ridge distance [RID], 180 cm; ridge bed width [RBW], 120 cm; ridge shoulder width [RSW], 90 cm; and furrow, 60 cm) and LAR2 (RH, 35 cm; RID, 160 cm; RBW, 100 cm; RSW, 70 cm; and furrow, 60 cm) in 2008, and LAR3 (RH, 35 cm; RID, 160 cm; RBW, 110 cm; RSW, 80 cm; and furrow, 50 cm) in 2009. In 2008, the LAR1 and LAR2 cultivations were not superior in root tuber yield to the CHR cultivation. In 2009, we investigated the yield properties by including the planting density factor (2.222, 1.852, and 1.500 hills m^-2) within the ridge cultivation modes (CHR/LAR3) and planting modes (CVP/TST). The lowest root tuber yield was obtained in the LAR3×CVP×1.852 treatment (3784 g m^-2). With respect to the two-factor interaction between ridge modes (CHR/LAR3) and planting modes (CVP/TST), the lowest yield was obtained in the LAR3×CVP treatment (4079 g m^-2), and under LAR3 conditions, the yield was higher under TST (5169 g m^-2) than under CVP at the 1% level. These results suggested that the TST method might be suitable, while the CVP method would be unsuitable, for the LAR3 cultivation. The results obtained in this study could be useful for future studies on ridge shape for sweet potato cultivation.

Among the challenges for intellectually disabled persons when they start farming is that the tasks they can be entrusted with are limited, and their production efficiency is reduced. In this study, we examined whether it would be possible to shorten the working hours of students with intellectual disabilities by combining “elementary process decomposition” （decomposition of a process to a task that can be done with only one action or repetition of that action） and assistance tools, along with cultivation in fiber-medium pots that take advantage of the existing fence. In the study, five students from a special-needs senior high school cultivated Japanese yam, for which there is concern about the lack of successor in the prefecture. Three surveys were conducted: （1） a descriptive survey of the students’ work style, （2） a comparative survey of work time involved in each process, and （3） a comparative survey of harvests obtained using different cultivation methods. We found that the students were able to carry out all processes independently except for sprouting, which required assistance by supporters. The total work time for all processes was 476 minutes with the conventional method and 313 minutes using the fiber-medium method, a reduction of 163 minutes; this difference was significant at the 0.1% level （p<0.001）. The fiber-medium method had a significantly greater yield than the conventional method, again at the 0.1% level（p<0.001）. On the other hand, the external shape of Japanese yam was significantly more spherical in the conventional method, at the 0.1% level. Together, these results show that students with intellectual disabilities can work independently and with reduced work time through a combination of elementary process decomposition, assistance tools, and cultivation in fiber-medium pots that take advantage of the existing fence.

This study investigated a suitable seeding method and timing of thinning on direct-seeded cabbage cultivation, aiming to shorten thinning labor. We compared a seeding method of sowing two seeds per 10 cm with a conventional seeding method (sowing two seeds), and thinned at two-leaves stage and six-leaves stage, respectively. The thinning time was significantly shorter in 10-cm seeding (2.0–3.1 s/hill) than in conventional seeding (4.7–4.9 s/hill), suggesting that the proposed seeding method was suitable to save thinning labor. In 10-cm seeding, thinning time at six-leaves stage was 1.1 s/hill shorter than that at two-leaves stage. The cabbage growth (leaf area and cabbage head weight) was not significantly affected by the timing of thinning, but the growth tended to be better in 10-cm seeding than in 0-cm seeding. These indicated that 10-cm seeding with thinned at six-leaves stage would be suitable for saving thinning labor and achieving a robust direct-seeded cabbage production.

To estimate onion yield in the sorghum–onion double-cropping system (DCS) and sweet potato–onion–sorghum–onion crop rotation system (CRS) in comparison with the onion mono-cropping system (MCS), four sets of three-year field experiments (two sets of DCS plus two sets of CRS) were conducted in the southern Kyushu region of Japan. This study demonstrates that in all four sets of field experiments, the onion bulb yields in the first onion cultivation were approximately 20% higher in DCS and CRS than those in MCS; however, when we continued the DCS and CRS to the second and third onion cultivations, the effect of bulb yield enhancement by DCS and CRS over MSC disappeared. The reason the yield-enhancing effect disappeared in the second and third onion cultivations was not clear; hence, further experiments are required with serial measurements of mycorrhizal infection rates and soil nutritional conditions to clarify the effect of DCS and CRS on onion growth and yield in the southern Kyushu region.