Calcium application strategy modulates nutrient partitioning, vegetative physiological status and fruit quality in persimmon (Diospyros kaki L.)

Calcium (Ca) nutrition is a key determinant of persimmon fruit quality, although its effectiveness is constrained by limited phloem mobility, nutrient partitioning and application timing. This study evaluated how root-applied Ca and foliar treatments combining Ca with silicon (Si) or boron (B) affected seasonal nutrient dynamics, leaf physiological status and fruit quality in ‘Rojo Brillante’ persimmon. Seasonal monitoring of macro- and micronutrients in leaves and fruit identified bloom as the stage showing the greatest treatment-related variability in nutrient concentrations and partitioning. Ca-based treatments primarily modulated nutrient redistribution between vegetative and reproductive tissues rather than increasing total nutrient uptake. Leaf chlorophyll content, estimated using the SPAD index, was strongly influenced by application strategy, with the combined Ca+Si foliar treatment maintaining higher SPAD values throughout vegetative development, indicating enhanced photosynthetic activity and source performance. At harvest, fruit quality attributes were not solely explained by crop load, as treatments with comparable fruit numbers showed contrasting outcomes in fruit size, firmness and colour development. The Ca+Si foliar treatment produced heavier and firmer fruit than the control (239 vs. 216 g and 43.5 vs. 39.5 N, respectively), while delaying colour development (colour index of 6.26 vs. 7.40). In contrast, Ca-root increased fruit retention (536 vs. 370 fruits per tree) but resulted in smaller and softer fruit (161 g and 37.1 N), highlighting the trade-off between crop load and individual fruit quality. Overall, the results underscore the importance of Ca application strategy and nutrient interactions in optimizing vegetative performance, nutrient balance and fruit quality in persimmon.