Agricultural Sciences: Techniques and Innovations Vol. 8

Rice (Oryza sativa L.) is the principal food crop in Asia, feeding over half of the world’s population. Its production, however, is constrained not only by biotic and abiotic stresses but also by the plant’s own allelochemical activity. Rice residues and by-products, especially rice bran, contain secondary metabolites that may cause autotoxic effects, potentially inhibiting the germination, growth, and yield of rice. Rice bran, derived from the outer layers of the grain during milling, is rich in nutrients and bioactive compounds. It contains lipids, proteins, vitamins, and minerals that contribute to both its functional value and its role in agricultural systems. This chapter examines the phenomenon of rice bran autotoxicity by synthesising experimental findings from greenhouse and laboratory studies and situating them within broader allelopathic research. The study employed laboratory germination assays and greenhouse experiments using a Completely Randomised Design with five replications and five extract concentrations (0–10%). Results indicated that aqueous rice bran extracts significantly reduced normal seedling germination, retarded radicle and plumule elongation, and diminished yield components such as panicle length, tiller number, and grain weight. The concentration threshold for severe autotoxicity lies between 5–10%, with IC₅₀ values for abnormal seedlings observed around 4.7%. Mechanistically, phenolic acids, flavonoids, and diterpenoids (momilactones) disrupt enzymatic activity, hormone regulation, and cellular redox balance. While these effects threaten crop establishment and yield when bran residues are mismanaged, they also suggest opportunities for eco-friendly weed control. Practical management strategies—such as composting, biochar conversion, and controlled application—can mitigate negative impacts while harnessing rice bran’s allelopathic potential. These findings highlight the importance of residue management in rice-based cropping systems where accumulation of allelopathic compounds may influence crop establishment.