Grafted transplants are widely used for watermelon culture in Korea mainly to reduce the yield and quality losses caused by soil-borne diseases. It is normal practice to cure the grafted transplants under high relative humidity (RH) and low photosynthetic photon flux (PPF) conditions for a few days after grafting to prevent the wilting of the transplants. Transpiration rate (TR) and net photosynthetic rate (NPR), however, could be suppressed under those environmental conditions. In the present study, TR and NPR of the grafted watermelon transplants were compared during graft union formation under 18 environmental conditions combining two air temperatures (20 and 28 °C), three RHs (60%, 80%, and 100%), and three PPF s (0, 100, and 200 μmol·m-2·s-1). Percentages of graft union formation and survival were also evaluated. TR and NPR dramatically decreased just after grafting but slowly recovered 2 to 3 days after grafting at 28 °C. The recovery was clearer at higher PPF and lower RH. On the other hand, the recovery of TR and NPR was not observed in 7 days after grafting at 20 °C. Differences in TR and NPR affected by RH were nonsignificant. Percentage of graft union formation was 98% when air temperature, RH, and PPF were 28 °C, 100%, and 100 μmol·m-2·s-1, respectively, which was the highest among all the treatments. Percentage of survival was over 90% when air temperature was 28 °C and RH was higher than 80% (when vapor pressure deficit was lower than 0.76 kPa). In addition, higher PPF enhanced TR and NPR and promoted rooting and subsequent growth of grafted transplants. Results suggest that the acclimation process for grafted watermelon transplants can be omitted by properly manipulating environmental factors during graft union formation.
We aimed to develop a more accurate transpiration model for cucumber (Cucumis sativus L.) plants to optimize irrigation and nutrient usage in soilless greenhouse cultivation. Accurate modeling of transpiration in greenhouse-grown cucumbers is crucial for effective cultivation practices. Existing models have limitations that hinder their applicability. Therefore, this research focused on refining the modeling approach to address these limitations. To achieve this, a comprehensive methodology was employed. The actual transpiration rates of three cucumber plants were measured using a load cell, enabling crop fresh weight changes to be calculated. The transpiration model was developed by making specific corrections to the formula derived from the Penman-Monteith equation. In addition, the study investigated the relationship between transpiration rate and solar radiation (Rad) and vapor pressure deficit (VPD), identifying a nonlinear association between these variables. The transpiration model was adjusted to account for these nonlinear relationships and compensate for Rad and VPD. Comparative analysis between the actual and estimated transpiration rates demonstrated that the developed cucumber transpiration model reduced overestimation by 23.69%. Furthermore, the model exhibited higher coefficients of determination and root mean square error (RMSE) values than existing models, suggesting its superior accuracy in predicting transpiration rates. Implementing the transpiration model-based irrigation method demonstrated the potential for ∼21% nutrient savings compared with conventional irrigation practices. This finding highlights the practical applications of the developed model—accounting for a nonlinearity of Rad and VPD—in optimizing irrigation practices for greenhouse cucumber cultivation.