Effect of organic mulches on weed suppression and yield of turmeric under rainfed conditions

Abstract:

Weed competition alone can slash turmeric rhizome yields by 40-60% under rainfed management, yet chemical herbicides are incompatible with organic certification requirements. A two-year field experiment (wet season 2022 and 2023) at Chiang Mai, northern Thailand, compared four organic mulch materials — paddy straw at 5 t ha⁻¹, sugarcane trash at 6 t ha⁻¹, dry teak (Tectona grandis) leaves at 4 t ha⁻¹, and coir pith at 3 t ha⁻¹ — against an un-mulched control for their ability to suppress weeds and improve turmeric (Curcuma longa cv. Pichit Golden) productivity. The experiment followed a randomised block design with four replications. Coir pith recorded the lowest weed density (13.8 plants m⁻²) and highest weed control efficiency (67.1%), followed by sugarcane trash (56.4%). Fresh rhizome yield was greatest under coir pith (27.5 t ha⁻¹), representing a 91.4% increase over the control (14.3 t ha⁻¹). Soil moisture at 15 cm depth during the dry spell of September remained 4.2 percentage points higher under coir pith than in bare plots. These findings support coir pith as the most effective single-factor weed management tool for organic turmeric growers in the northern Thai highlands.