Mitigating High-Temperature Stress through Organic Manure Amendments on the Growth of Lunuwila (Bacopa monnieri (L.) Wettst.)

Lunuwila (Bacopa monnieri), typically found in semi-aquatic environments, is increasingly threatened by habitat loss due to environmental degradation and rising temperatures associated with global warming. This study aimed to identify an optimal organic manure treatment to counteract the adverse effects of increased temperatures on Lunuwila growth. The experiment was conducted at The Open University of Sri Lanka, Nawala, inside a temperature-controlled polytunnel designed to simulate the increased (34-35°C) temperature conditions and plant house at ambient (27-32°C) temperature. A two-factor factorial completely randomized design (CRD) with three replications was used to assess the interaction between temperature and organic manure on Lunuwila growth. The treatments included two temperature levels: ambient temperature (T1) and increased temperature (T2), and four organic manure levels: 100% compost (M1), 50% compost with 50% cow dung (M2), 100% cow dung (M3), and a no-fertilizer control (M0). Organic manure was applied at a rate equivalent to 10 tons per hectare for 100% treatments. Growth parameters were analysed using R Studio software (version 4.2.1), with treatment differences tested by Analysis of Variance (ANOVA) and Duncan’s Multiple Range Test (DMRT) for mean comparison at a significance level of p=0.05. Results indicated that 100% compost under elevated temperature significantly (p<0.05) enhanced shoot length (90.7% increase), leaf count (674.4±39.5), branch count (13.93±1.01), leaf area index (43.05±2.45), root length (8.54±0.05 cm), chlorophyll content (41.7±0.27 SPAD), fresh shoot weight (2583.84±0.56 g/m2), dry shoot weight (267.45±0.22 g/m2), fresh root weight (70.41±0.26 g/m2), and dry root weight (8.79±0.03 g/m2) compared to the control at p≤0.05. Conversely, stem diameter (0.381±0.01 cm) was greatest under ambient temperature with 100% cow dung, and root diameter (0.43±0.004 cm) was highest with 50% compost and 50% cow dung under ambient conditions. Therefore, even in a global warming situation 100% compost is favourable for the sustainable cultivation of Lunuwila.