Effects of partial sheet mulching on fruit quality and yield of early maturing satsuma mandarin (Citrus unshiu Marc.) trees

Effects of partial sheet mulching (PSM) on fruit quality and yield were investigated in early maturing satsuma mandarin (Citrus unshiu Marc.) trees grown on deep granite soils. Effects of different sheet covering area, duration and direction to contour line were determined. 1. With 'Ichifumi-wase' trees, leaf water potential (LWP) was held at approximately -0.7 MPa throughout the experiment in 90% and 70% PSM, while lower LWP was noted in 100% PSM. The sheet mulching significantly increased juice soluble solids content (SSC) compared with non-treated control. The highest SSC was observed in 100% PSM. Development of rind color was promoted by the treatment except 70% PSM. Greater juice titratable acidity was noticed only in 100% PSM than control. These results indicate that partial sheet mulching should be 80-90% for high quality fruit production in deep granite soils. 2. With 'Nichinan-ichigo' trees, 90% PSM in which covering was started from early season(May and June) produced fruit with average SSC greater than 12deg having higher a* value rind color. 3. Regarding the effect of sheet covering direction to contour line, with 'Miyagawa-wase' trees, SSC showed 1.7deg and 0.9deg greater than control at right angle to contour line and at parallel with contour line, respectively. Juice sugar content showed similar trends. There was no significant difference in juice titratable acid content between treatment and control. The rind coloration was promoted by PSM treatment. No or little differences were in fruit sizes, weight or yield among treatments. The PSM treatment tended to increase starch content of roots, branches and leaves in the winter, which seemed to increase the number of flowers and new shoots in the following season. 4. As a result, 90% PSM from early season (May and June) is effective to produce high quality fruit in early maturing satsuma mandarin trees without reducing number of flowers caused by drought stress.