Tropical Legume for Turmeric (Curcuma longa L) Cultivation in Okinawan Red Soil, Japan.

Leguminous plants supply nutrients and organic matter, and soil properties as well as yield and quality of turmeric. Two pot experiments were conducted to investigate the effects of four legume crops on the growth, yield and quality of turmeric in red soil. Exp.1 was conducted in May 16, 2015 to January 01, 2016 using four treatments, (1) Only 10 kg soil, (2)10 kg soil+0.5 kg hairy vetch, (3) 10 kg soil+1.0 kg hairy vetch and (4)10 kg soil+1.5 kg hairy vetch. Each treatment was replicated 15 times. Exp.2 was conducted in June 15, 2016 to December 20, 2016 using four treatments, (1) Only 10 kg soil, (2) 10 kg soil+350g fresh soybean, (3)10 kg red soil+350g fresh mungbean and (4)10 kg red soil+350 g fresh dhaincha.

Hairy vetch treated turmeric plants survived longer and provided higher growth parameters, shoot biomass and yield compared to control plants. Highest yield (521.84 g plant^-1) was found in 1.5 kg hairy vetch treated plants. Curcumin content in the rhizome of turmeric decreased with hairy vetch application compared to control. Hairy vetch maintained the soil pH 7.52 to 7.84 and decreased soil bulk density from 0.68 to 0.60 (g cm^-3). Turmeric plants treated with soybean, mungbean and dhaincha survived longer and resulted in significantly higher growth parameters, shoot biomass and yield compared to those with the control plants. The highest turmeric yield was obtained with mungbean (213 g plant^-1) followed by dhaincha (176.9 g plant^-1) and soybean (166.4 g plant^-1). These studies showed that all the legumes improved soil physical and chemical properties, supplied nutrients and enhanced turmeric yield but decreased its quality.