Phenological Patterns and the Impact of Seed Burial Depth and Scarification on the Emergence and Growth of Redweed (Melochia corchorifolia)

Abstract

Redweed a tropical erect branched herb, is one of the predominant broadleaf weeds affecting upland crops in the Onattukara Sandy Plains, Kerala, India. Experiments were conducted in a screenhouse at the College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, India, to determine the effects of seed burial depth and seed scarification on emergence indices and growth attributes of redweed. Scarification stimulated emergence and resulted in greater values for emergence indices and seedling parameters. The seedling emergence of redweed was influenced by seed burial depth. Shallow seed burial (2 cm) of scarified and non-scarified seeds resulted in greater seedling length (70 cm and 58 cm, respectively), seedling biomass (0.72 g and 0.48 g, respectively), emergence percentage (60% and 32%, respectively), and greater values for other emergence indices. As the depth of seed burial increased from 2 cm, emergence and seedling biomass decreased, exhibiting lower values for the emergence indices. Correlation and regression studies revealed that seed burial depth of scarified and non-scarified seeds greater than 2 cm had a negative effect on seedling emergence and biomass of redweed. Weed biology studies indicated that redweed displayed notable consistency in its phenological traits, regardless of the location where the seeds were collected, as little ecotype variability was observed. Emergence occurred in 6 d, 50% flowering in 44 d, capsule formation in 56 d and maturity in 76 d. On average, a single plant produced 277 seeds and had a 100 seed weight of 0.31 g. A stale seedbed with shallow tillage or deep plowing to a depth of 10 cm before sowing can be adopted to reduce the infestation of redweed.