Abstract
Recently, in Japan, lowering of soil moisture by mulching has been widespread in satsuma mandarin cultivation in order to increase the sugar content of the fruit. In this study, the performance as mulch of some materials, such as white porous waterproof sheets and nonrigid plastic (PE and PVC) films in various colors, was compared. We investigated the physical properties and the effects of such materials on soil moisture, gaseous environment in the rhizosphere, radiation environment and fruit quality. The white porous waterproof sheet and an aluminized PE film with high reflectivity activated coloring and increased brix of the fruits in lower and inner tree canopies, because these materials improved the radiation environment. Some fruits, however, were severely sunburned by strong reflected rays from the aluminized PE film. Moreover, the rays from the film were very dazzling. The porous waterproof sheet with high gaseous permeability decreased water content of soil effectively and kept CO2 concentration low in the rhizosphere, although the concentration became considerably higher under nonrigid plastic films with little gaseous permeability. The sheet was expected to avoid gaseous stress on roots. Thus we conclude that white porous waterproof sheets with high reflectivity and gaseous permeability are more useful as mulch materials in satsuma mandarin cultivation than nonrigid plastic films.
