Effect of Sweet Sorghum Cultivation and Residual Application Method on Yield and Curcumin Content in Turmeric Rhizomes

The objective of this study is to evaluate the influence of sweet sorghum (SS) cultivation and the application of SS aboveground residues on growth, yield and curcumin content of turmeric. The soils in SS cultivation area and SS non-cultivation area were placed into Wagner pots (diameter: 16 cm, height: 19 cm) in a greenhouse. The pots with SS cultivated soil and SS non-cultivated soil were subjected to four treatments: (1) no fertilizer (NF) , (2) chemical fertilizer (CF) , (3) CF with SS residue incorporation into the soil (INC) , and (4) CF with SS residue surface application (SUR). One seed-rhizome (20 g) of turmeric per pot was planted on June 2, 2017. The aboveground portion and rhizome of turmeric were harvested on December 6, 2017. The exchangeable K2O concentration in SS cultivated soil was significantly higher than that in SS non-cultivated soil before turmeric planting. Soil moisture content in the early growth stage of turmeric was higher in SUR than in other treatments in both SS cultivated and non-cultivated soils. Dry weight and curcumin content of turmeric rhizome at harvest were higher in SS cultivated soil than in SS non-cultivated soil and was higher in SUR than in other treatments. From these results, SS cultivation increased soil exchangeable K2O concentration and SS residue surface application increased soil water retentivity, which might increase the yield of turmeric and curcumin content.