Green Manure Plants Influence Growth, Yield and Curcumin Content of Turmeric (Curcuma longa L.) in Dark-red Soil in Okinawa, Japan

抄録

Using green manure plants is a common practice for crops in light-texture soil with low organic matter content. The effects of the application of crotalaria (Crotalaria spectabilis L.) and hairy vetch (Vicia villosa R.) green manure plants on the growth and yield of turmeric (Curcuma longa L.) were evaluated in dark-red soil in Okinawa, Japan. Dry green manure of crotalaria or hairy vetch was applied at the rate of 81.43-82.86 g per turmeric plant in field experiment. This rate provided 2.52-2.74 g N, 0.11-0.12 g P and 0.89-0.95 g K per turmeric plant. In glasshouse experiment, 250.00 g dry green manure of crotalaria or hairy vetch per turmeric plant was applied and the rate provided 7.62-8.43 g N, 0.33-0.36 g P and 2.70-2.91 g K. The manures maintained the soil pH at 6.5-7.0 and reduced the soil bulk density by 19%. In the field, turmeric yield (rhizome) increased by 7-10% with the application of green manure plants. In the glasshouse, shoots remained green 30 days longer, and plant height, tiller number, leaf dry matter content, shoot dry matter content and yield increased by 20, 76-165, 157-184, 173-197 and 28-86%, respectively, when turmeric was grown with the application of a 3-times higher amount of green manure plants, compared to that in the field experiments. Hairy vetch alone provided 46% higher yield, while crotalaria provided similar yield, compared to the fertilizer treatment. Curcumin concentration (%) in the rhizomes was lower by 4-54%, presumably due to the excessive amount of N supplied by the green manure plants and lower K nutrient content. The current study demonstrated that green manure plants provided nutrients and improved some of the physical and chemical properties of dark-red soil, which significantly enhanced the growth and yield of turmeric.