Agronomic Strategies to Manipulate Kiwifruit Calcium Content to Understand Its Role in Fruit Physiology

Calcium (Ca) is one of the most important nutrients involved in fruit quality and storability; therefore, its application in fruit trees is often used in pre- and post-harvest. The aims of this study were to manipulate soil Ca, K, and N availability, photosynthetic active radiation, and fruit transpiration rate to understand their implication on fruit Ca accumulation on green-flesh kiwifruit grown in calcareous soil. Our results show that Ca partitioning into the fruit is not affected by the applications of Ca, K, and N, as well as the increase of photosynthetic active radiation. However, the presence of reflective films reduced fruit firmness and increased soluble solid content at harvest and during cold storage, thus enhancing fruit quality. Fruit calcium accumulation is decreased by the reduction of fruit transpiration rate; however, it has the possibility to recover, even close to fruit harvest, when the fruit transpiration is restored. The presence of bags reduced fruit weight from 84 to 63 g even though bags were removed. Our data provide evidence of the inefficiency of calcium fertilization in kiwifruit in calcareous soils and demonstrate the extension of calcium transportation into the fruit, which seems to occur during the entire growing season.