Optimal Planting Depth for Turmeric (Curcuma longaL.) Cultivation in Dark Red Soil in Okinawa Island, Southern Japan

Effects of planting depth on emergence, growth, development and yield of turmeric (Curcuma longaL.) in dark red soil (Shimajiri Mahji) were evaluated in Okinawa, Japan. Turmeric planted at the depths of 8, 12 and 16 cm emerged earlier and more evenly than that planted at a shallower depth in both glasshouse and field experiments. Weed growth was unaffected by the planting depth of turmeric until 50-60 days after planting (DAP), but affected thereafter due to mutual shading with the canopy. Weed biomass at 90-140 DAP was significantly smaller in the fields where turmeric was planted at the depths of 8, 12 and 16 cm than in the field where it was planted at a shallower depth. The turmeric rhizome (yield) developed earlier when planted at 8, 12 and 16 cm depths than at 4 cm. In a glasshouse study, shoot biomass and yield of turmeric were significantly greater when planted at the depths of 4, 8 and 12 cm than that of 2 cm. In field experiments, they were also significantly greater when planting depth was 8 or 12 cm than 4 cm. Even in turmeric planted at a 16 cm depth shoot dry weight and yield were greater than that planted at a 4 cm depth, but it was comparatively difficult to harvest rhizomes in this field. About 30% of turmeric in the field planted at a 4 cm depth was uprooted by a typhoon, but not at the depths of 8, 12 and 16 cm. The over all results suggested that rhizomes of turmeric should be planted at a depth of 8 to 12 cm in dark red soil for a higher yield and lower weed competition