Optimizing bioherbicide application timing and plant spacing to manage weed growth in rice (Oryza sativa L.) cultivation

Weed management is crucial for successful rice cultivation. Bioherbicides derived from cogon grass extract offer a promising solution for weed control. Additionally, optimizing plant spacing has been recognized as an effective method to suppress weed growth. Thus, this study aims to investigate the impact of cogon grass extract application timing and plant spacing on weed growth in rice cultivation. The study was conducted from October 2022 to February 2023 in the Special Region of Yogyakarta, Indonesia. The study was 3 × 2 factorial and arranged in a randomized completely block design (RCBD). The first factor was the bioherbicide application timing: control (no application), three days before planting, and at the time of planting. The second factor was plant spacing: 15 × 15 and 25 × 25 cm. In total, there were six treatment combinations and three replications (replications as blocks). The research results indicated the application timing of bioherbicide did not significant effect on the growth of weed and rice, as well as the grain dry weight. Fimbristylis miliacea was obtained as the dominant weed species. Bioherbicide application at the time of planting could alter the composition of weed species compared to the control in plant spacing of 15 × 15 cm. Furthermore, the plant spacing of 25 × 25 cm resulted in higher grain and weed dry weight (19.40 g/clump and 45.00 g/0.25 m2) compared to 15 × 15 cm (12.92 g/clump and 23.04 g/0.25 m2). On the contrary, the grain dry weight per hectare was higher in 15 × 15 cm (5.74 t/ha) than in 25 × 25 cm (3.10 t/ha). The research findings indicate that closer plant spacing can suppress weed growth and increase the grain dry weight per hectare compared to wider plant spacing. We recommend that the use of cogon grass extract dosage needs to be increased above 50 L/ha.