Development of ‘Shielding-mulch Cultivation’ for High-quality Fruit Production of Satsuma Mandarin

Abstract

In the production of satsuma mandarin (Citrus unshiu Marcow.) in Japan, mulch cultivation, which induces drought stress in trees, is often used for high-quality fruit production. However, there are cases in which drought stress has not been induced because rainwater flows into the root area, and the roots extend out of the mulching sheet. Therefore, I have developed ‘shielding-mulch cultivation’ (‘S. mulch’), a method of mulching the planting row and surrounding the root area with an exclusive plastic sheet (‘S. sheet’, width: 500 mm; thickness: 1.5 mm; length: 30 m; material: high-density polyethylene) under drainage-designed field conditions. This study verified the usefulness of this technology. The effects of drought stress on trees and soil moisture in the root area under ‘S. mulch’ and conventional mulch cultivation were investigated. As a result, the maximum water potential in the leaves (ψmax) of ‘S. mulch’ was controlled to –0.7 to –1.0 MPa, which is appropriate for high-quality fruit production. On the other hand, ψmax of conventional mulch cultivation was not suitable for high-quality fruit production. In addition, the soil moisture of ‘S. mulch’ was lower than that of conventional mulch cultivation during the fruit growth period. As is characteristic of fruit with induced drought stress, the fruit of ‘S. mulch’ at harvest had a higher sugar content, slightly higher acidity, and smaller fruits with a strong reddish skin color as compared with fruit produced with conventional mulch cultivation. Therefore, it was suggested that ‘S. mulch’ can stably produce high-quality fruits by reliably inducing drought stress.