Seed germination characteristics of chocolate weed (Melochia corchorifolia L.): Responses to flooding and mulching regimes

Red weed (Melochia corchorifolia L.), locally known as chocolate weed, is an aggressive annual broad-leaved weed widely prevalent in tropical agro-ecosystems. Its rapid growth and ecological plasticity cause severe interference during crop establishment in both upland and lowland systems of the Onattukara Sandy Plain of Kerala, India. To elucidate the effects of seed scarification, paddy straw mulching and flooding on germination behaviour, pot culture experiments were conducted under rain-shelter conditions at the Onattukara Regional Agricultural Research Station, Kayamkulam. The experiments were laid out in a completely randomized design with 2 factors: seed scarification (non-scarified and mechanically scarified) as the first factor and different rates of paddy straw mulching (0, 250, 500, 750 and 1000 g m-2) and flooding depths (0, 1, 2, 3, 4, 5, 6 and 7 cm) as the second factor. Scarified seeds exhibited higher germination percentage, faster germination, lower mean germination time, earlier attainment of 50 % germination and superior germination indices compared to non-scarified seeds. Flooding strongly inhibited germination, with a progressive decline as water depth increased. Complete suppression was achieved at a flooding depth of ≥ 4 cm, irrespective of scarification. In contrast, paddy straw mulching did not significantly influence germination or germination indices, even at higher mulch levels. Overall, M. corchorifolia germination is governed primarily by dormancy release through scarification and hydrological conditions rather than surface mulching. Management strategies emphasising minimal soil disturbance and maintenance of ≥ 4 cm flooding are therefore more effective in managing red weed in rice-based systems of the Onattukara Sandy Plain.