Planting Dates to Mitigate Climate Variability Effects on Phenology and Yield of Faro-66 and Rok-34 Rice Under Rain-fed Conditions in Sierra Leone

Rice (Oryza sativa L.) production in Sierra Leone, a staple food for both diet and the economy, is severely constrained by climate variability, particularly erratic rainfall patterns that disrupt traditional planting calendars. Identifying adaptive strategies, such as optimizing planting dates for specific varieties, is critical for enhancing resilience and food security. This study evaluated the impact of six planting dates (from April 1 to June 15) on the phenology and yield of two widely cultivated rice varieties (FARO-66 and ROK-34) under rain-fed conditions in Southern Sierra Leone. A field experiment was conducted during the 2022 cropping season using a Split-Plot Design (SPD) with three replications. Physiological parameters (plant height, tiller count, leaf number) were monitored bi-weekly. Yield and yield components (number of panicles, number of spikelets, grain weight, and biomass) were measured at harvest. Data were analyzed using ANOVA and multivariate analyses in R. Planting date had a highly significant effect (p<0.001) on all measured traits. ROK-34 demonstrated superior performance in early plantings (April), achieving significantly greater plant height (+17.8 cm on average, p<0.0001) and higher yield. However, its performance declined sharply under late planting (June). On the other hand, FARO-66 showed greater phenotypic plasticity, maintaining more stable leaf numbers and yield components across a wider planting window, making it more resilient to delayed sowing up to late May. Multivariate analysis revealed divergent stress response mechanisms: ROK-34's yield was source-limited, correlating positively with biomass (r = 0.87), while FARO-66's yield was primarily sink-limited, constrained by grain abortion (unfilled grains, r = -0.79) under terminal stress. The optimal planting strategy is variety-specific. ROK-34 is the optimal choice for early-season planting to maximize yield potential, while FARO-66 serves as a critical resilient option for farmers facing delayed rainfall. The significant differences in yield and phenotypic plasticity between FARO-66 and ROK-34, underline the necessity for variety-specific adaptive planting date strategies, with FARO-66 providing a crucial resilience option for farmers facing delayed onset of rains. It furthers provides evidence-based guidelines for climate adaptation, advocating for the integration of variety-specific planting calendars into national extension services to mitigate yield losses and enhance food security in rain-fed systems in Sierra Leone. Key words: Climate adaptation, sowing date, Oryza sativa L., genotype-environment interaction, rain-fed agriculture