Large fluctuations in fruit set and fresh yield are issues associated with the production of sweet pepper. Fluctuations in fresh yield (i.e., flush) result in improper labor distributions and price fluctuations for growers. Modeling the fruit set is a promising way to improve the profits of growers and allow the arrangement of labor distribution and logistics. Therefore, this study aimed to develop a model for predicting the short-term yield changes of sweet pepper by integrating two sub-models: one model for predicting the production of total dry matter and one model for predicting the individual fruit growth. We hydroponically grew four sweet pepper cultivars (Artega, Nagano, Nesbitt, and Trirosso) in a greenhouse to investigate the accuracy of the proposed model. Comparisons between observed and predicted fresh yields showed that the peaks and troughs of fresh yields were accurately predicted, regardless of cultivar differences. The average root mean square error between them was within the range of 0.24 to 0.39 t⋅ha−1⋅d−1. Therefore, growers will be able to predict short-term yield changes of sweet pepper by obtaining coefficients for predicting the production of total dry matter and fruit growth curve of the cultivar scheduled to be cultivated.
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.