To improve the yield of sweet peppers in Japan, we investigated the relationships between plant growth characteristics and fruit yield, with a particular focus on dry matter production. Fruit fresh weight (i.e., fruit yield) was highly correlated with fruit dry weight. Aboveground dry matter production was correlated with both light use efficiency and intercepted photosynthetically active radiation. Although the number of fruits was correlated with the fruit set ratio, no correlation was found between the number of fruit and fraction of dry matter distributed to fruit. The correlation between the fraction of dry matter partitioned to fruit and fruit dry weight varied by plant stage, potentially due to the yield fluctuation called "flush". Together, these findings suggest that to improve the yield of sweet peppers in Japan, we should focus first on improving light use efficiency.

Agrivoltaic systems, comprising photovoltaic panels placed over agricultural crops, have recently gained increasing attention. Emerging interest in these systems led us to investigate their influence on rice crops. Various factors affecting rice crop yield, including fertilizer application, temperature, and solar radiation, were directly observed, and measured to evaluate changes associated with the shading rates of photovoltaic systems installed above rice crops. The results suggest that the allowable upper limit of the shading rate for agrivoltaic installations ranges from 27 to 39%, which sustains at least 80% of the rice yield, a condition set by the Japanese Ministry of Agriculture, Forestry and Fisheries for these systems. If such systems are applied to rice paddies in Japan at 28% density, they could generate 284 million MWh/yr. This is equivalent to approximately 29% of the total Japanese electricity demand, based on 2018 calculations. This projection indicates the potential of agrivoltaic systems for efficient land use and sustainable energy generation.

We investigated the relationships among the fruit set, dry matter production, and source-to-sink ratio of sweet pepper (Capsicum annuum) plants grown in a greenhouse. We quantified daily fruit sink strength per stem (st) at m days after transplanting (SSTm_st) by modeling the fruit growth curve. The daily total dry matter production (TDMm_st) was calculated and defined as the source strength. During an experiment lasting ≈250 days, the fruit set ratio [number of fruit harvested/number of flowers (FSRm)] decreased significantly with increases in both the weekly average SSTm_st from 9 days before anthesis (DBA) to 13 days after anthesis (DAA) and the weekly average fruit number (FRNm_st) from 9 to 1 DBA. FSRm increased significantly with increases in both the weekly average TDMm_st from 1 to 13 DAA and the weekly average source-to-sink ratio [source strength/fruit sink strength (SSRm_st)] from 5 DBA to 13 DAA. During the whole experimental period, significant positive correlations with FSRm were observed for TDMm_st and SSRm_st, and significant negative correlations with FSRm were observed for SSTm_st and FRNm_st. FSRm increased until approximately the time when the weekly average SSRm_st at 1 to 7 DAA (anthesis to 156°C⋅d−1) ranged from 1.0 to 4.0; then, it showed a saturation curve at SSRm_st values more than 4.0 (R2 = 0.81). These results suggest that it is possible to moderate the fluctuations in sweet pepper yield by monitoring the SSRm_st and the number of fruit set.