Impact of sowing time and integrated weed management approaches on weed dynamics, crop growth and yield in dry-direct seeded rice

Introduction

Rice (Oryza sativa L.) is one of the most important cereal crops globally. It serves as the primary staple food for more than half of the world's population. It is cultivated across diverse agroecological regions and plays a vital role in food security, particularly in Asia. It is estimated that global rice production will reach about 541.66 million metric tons in 2024-25, grown on nearly 172.54 million hectares of land (USDA, 2026) [23] . Among all countries, India and China are the leading producers. Together, they contribute a major share of global production of rice. India is currently the largest rice producer in the world, producing around 150 million metric tons of rice from about 51.42 million hectares during 2024-25 (USDA, 2026) [24] . In India rice is typically cultivated by traditional puddled transplanted method, which involves raising a nursery from seeds and then planting the seedlings in the field. This rice cultivation system is increasingly challenged by rising labour costs, declining water availability and the need for improved resource use efficiency. As a result, direct-seeded rice (DSR) has gained attention as water, labour and energy saving alternative that can shorten cropping cycles and reduce production costs (Phukan et al., 2021) [15] . The DSR method can be further divided into the wet direct seeded rice method (WDS) where, pre-germinated seeds are sown into the soil using a drum-seeder and the dry direct seeded rice method (DDSR), where, dry or ungerminated seeds are sown directly using broadcast, drilled or dibbled method into dry and prepared soil (Fikriyyah et al., 2019). Some research studies have shown that DDSR reduces weed infestation and increases yields by up to 75% (Shekhawat et al., 2020) [19] . Despite these advantages, DSR is more vulnerable to weed infestation than flooded transplanted systems because aerobic soil conditions during crop establishment favour the germination of a diverse weed flora (grasses, sedges and broadleaves). Severe early-season weed competition in DSR can markedly reduce tiller survival, panicle formation and final grain yield; reported approximately 90% of crop yield losses under uncontrolled weed pressure in DSR (Ahmed, Salim, & Chauhan, 2014; Shekhawat et al., 2020) [1,19] . Therefore, effective weed management in DSR is crucial not only to reduce competition and protect crop growth, but also to achieve economic sustainability. Integrated methods combining manual, mechanical, and chemical control are a promising way to reduce weed density and increase crop productivity. The date of sowing is a non-monetary, agronomic factor that strongly influences both crop performance and weed dynamics. Sowing time determines the environmental conditions (soil moisture, temperature and rainfall timing) during germination and early growth, which in turn affect weed emergence patterns and crop competitive ability. Early sowing may coincide with favourable conditions for weed germination and create a high initial weed flush, while an appropriately timed or slightly delayed sowing can reduce early weed pressure by avoiding peak flushes (Zhang et al., 2023; Mir et al., 2024) [26,13] . Thus, optimizing sowing date is an important cultural measure for reducing weed interference and improving crop establishment in DSR. However, use of herbicide mixtures that combine two or more active ingredients with different modes of action and can be applied sequential as pre-emergence followed by post emergence treatments throughout the growing seasons, reduces the seedbank of weeds and provide effective weed control against complex weed flora (Choudhary and Mishra, 2023; Sondhia et al., 2024) [, 20] . Consequently, integrated weed management (IWM) strategies that combine PE herbicides to suppress the initial flush, PoE herbicides to control escapes and at least one manual or mechanical weeding are recommended to achieve season-long weed control and sustain yields (Mir et al., 2024) [13] . A recent study demonstrates that combining optimum sowing time with effective weed management strategies, reduce weed infestation, improves crop growth, yield and economic benefits in DDSR. Therefore, a study was undertaken to assess the combined effects of different sowing dates and weed management approaches on weed flora composition, weed density and dry weight, weed control efficiency and yield performance of dry-direct seeded rice under Kharif seasons in Tarai reason of Uttarakhand. The objective was to identify optimum sowing date with weed management combinations that minimize weed competition, improve crop growth and maximize productivity of DDSR. The observations related to weeds were recorded at 60 and harvest stage for weed density and dry weight using a 0.5 x 0.5m quadrant at two random locations within each plot. Weed dry weight was recorded after sun drying the weed samples placed into the hot air oven at ±70°C temperature till constant weight gained. The data on weed density and dry weight were subjected to square root transformation √x + 0.5 before statistical analysis. Weed Control efficiency (WCE) was calculated based on data recorded at 60 DAS and at harvest stage in DDSR as per standard formula given by Mani et al. (1973) [12] . Formula used for calculating WCE -:

Materials and Methods

Where, WDTc = Weed dry weight in control plot (Weedy check) WDTt = Weed dry weight in treated plot Yield parameters (no. of panicles/ m 2 and grain yield in t/ha) were measured after harvesting of rice crop. [13] . Date of sowing and weed management practices significantly affected total weed density, dry weight and weed control efficiency (WCE) at 60 DAS and harvest stage in both years of 2023 and 2024. The lowest total weed density and dry weight at 60 DAS and at harvest were consistently recorded with D 3 -20 th June sowing i.e. 93. 93 [9,14,25,8] , which emphasized that integrated weed management strategies provide sustained weed control comparable to repeated manual weeding in dry direct seeded rice. Overall sowing on 20 th June combined with integrated herbicide application and timely hand weeding proved most effective in minimizing total weed density and weight and maximizing weed control efficiency under Kharif conditions.

Results and Discussion

Effect on yield attributes and grain yield

Number of panicles /m² was significantly influenced by sowing date during Kharif 2023 and 2024. The highest panicle density was recorded under D3-20 th June sowing (186.2 and 177.9 panicles/m²), which was superior to other sowing dates. The enhanced panicle number under mid-June sowing may be attributed to improved tiller survival and efficient assimilate partitioning toward reproductive sinks, supporting earlier findings of higher panicle density under optimum sowing windows (Shanta et al., 2020) [18] . Weed management practices also exerted a significant effect on panicle number. Among treatments, W 2 -pendimethalin 38.4% + pyrazosulfuron 0.85% (RM) 785 g/ha fb penoxsulam 21.7% SC 93.7 g/ha fb one hand weeding at 40 DAS, produced the highest panicles/m 2 (218.7 and 207.2), which was statistically at par with W4 (three hand weeding at 20, 40 and 60 DAS) (217.9 and 204.9). Both treatments were markedly superior to the weedy check (W5), which recorded the lowest values (82.8 and 74.6 panicles/m² in 2023 and 2024, respectively). The increased production of fertile tillers under effective weed control indicates that minimizing early crop weed competition promotes vegetative vigor and reproductive sink development, in close agreement with Sanodiya and Singh (2017) [16] ; Kaur et al. (2023) [10] . Sowing date significantly influenced grain yield of direct-seeded rice during both years. D 3 -20 th June sowing produced the highest grain yield (4.1 and 5.0 t/ha in 2023 and 2024), whereas D 1 -1 st June recorded the lowest yield (2.9 and 3.6 t/ha), followed by D 2 -10 th June (3.3 and 4.0 t/ha). These findings in close agreement with Kumar et al., 2012 [11] . Weed management practices also exerted a significant effect on yield. Treatment W 2 [pendimethalin 38.4% + pyrazosulfuron 0.85% (RM) 785 g/ha fb penoxsulam 21.7% SC 93.7 g/ha fb one hand weeding at 40 DAS] recorded the highest grain yield (4.6 and 5.7 t/ha), which was statistically comparable with W 4 -three hand weeding at 20, 40 and 60 DAS, (4.5 and 5.6 t/ha) during 2023 and 2024. In contrast, the weedy check (W 5 ) produced the lowest grain yield (0.7 and 0.9 t/ha). The superiority of W 2 among herbicide-based treatments is attributable to its higher weed control efficiency and broad-spectrum suppression of weed flora, which agrees with previous reports emphasizing the benefits of integrated weed management in dry direct seeded rice (Bhurer et al., 2013; Joshi et al., 2015; Sanodiya and Singh, 2017) [2,7,16] . The superior grain yield under D 3 -20 th June sowing was associated with lower weed density and weight, which reduced competition for light, nutrients, water and space, thereby enhancing crop growth and productivity. Similar relationships between reduced weed pressure and improved yield performance have been documented by Sanodiya and Singh (2017) [16] ; Swathi et al. (2024) [21] . The relationship between total weed dry weight at harvest stage and grain yield was examined using correlation and regression analysis based on the pooled data of two years. The results revealed a strong negative linear relationship between weed dry weight and grain yield, indicating that as weed dry weight increased, grain yield consistently decreased. The fitted regression equation (y = -0.01x + 5.27) indicates that for every unit increase in weed dry weight, grain yield decreased by approximately 0.01 t/ha. The R 2 value (0.93) suggests that about 93% of the variation in grain yield is explained by weed dry weight, indicating a very strong relationship between the two variables. Similar findings have been reported by Kaur et al. (2025) [10] ; Sar et al. (2024) [17] , who observed a significant negative correlation between weed dry matter and grain yield in direct-seeded rice and reported that higher weed dry weight resulted in reduced crop growth and yield due to severe competition throughout the crop growth period.

Conclusion

The findings of the present study indicated that the optimum sowing time with integrated weed management strategies plays a crucial role in regulating weed dynamics and improving crop productivity in dry direct seeded rice. The experiment concluded that sowing on 20 th June, combined with an integrated sequential application of pre-emergence (PE) treatment of pendimethalin 38.4% + pyrazosulfuron 0.85% (RM) at 785 g/ha, followed by a post-emergence (PoE) application of penoxsulam 21.7% SC at 93.7 g/ha and supplemented with one hand weeding at 40 DAS, found to be the most effective treatment combination to supressing mixed weed flora. This approach resulted in reduced total weed density and dry weight, higher weed control efficiency, improved crop growth and more tiller survival and more panicle formation which ultimately resulted in higher grain yield under dry direct seeded rice condition. Thus, timely sowing along with integrated sequential herbicide application supplemented with manual weeding can be recommended as an efficient and sustainable weed management strategy for improving productivity in dry-direct seeded rice during the Kharif season.

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