Effect of Different Integrative Weed Management Tactics on Paddy (Oryza sativa L.) during kharif in terai Region of West Bengal

Paddy (Oryza sativa L.) is one of the vital crops in Asian countries, the staple cereal of over 50% of the people worldwide and provides about 20% of the world’s dietary energy supply (FAO International Year of Rice, 2004). Paddy is a preliminary source of foodgrain for greater than one third of the world’s population, basically in Asia, Africa and Latin America (Hasamuzzaman et al., 2009). The second most common cereal consumed by people is paddy next to wheat.

Worldwide, 530 million tonnes of paddy are obtained from 150 million hectares of land annually, providing an average yield of 3.5 t ha^-1 and 21% of the food calorie of world’s population. Almost 9/10^th of paddy is grown in the continent, Asia (Zimdahl, 1988 and McDonald, 1994). The current yield of paddy in our country is lesser than mean grain yield of paddy in the world. One of the major factors responsible for low productivity of paddy is weed because of its multiple harmful impacts. Uncontrolled weed population decreased the grain productivity by 75.8, 70.6 and 62.6% under dry direct-seeded paddy, wet direct-seeded paddy and puddled transplanted paddy, respectively (Singh et al., 2005).

Paddy production in our country faced loss of 15 million tonnes every year only because of weed competition in the 20^th century (Chattarjee and Maity, 1981). In upland ecosystem of paddy, yield reduction calculated from the weed density and dry weight, varies from 30-100% (Jensen et al., 2001). In the world, 10% deterioration in agricultural production is often allotted to the competitive nature of weeds in the situation of following proper control measures. Direct-seeded paddy is extensively grown by the farmers to cut back the cost of cultivation but the jungle rice drastically diminishes the yield of cultivated rice (Lee et al., 2004 and Seal et al., 2005). The upland crop of paddy faces a tremendous crop-weed competition upto 40 days followed by sowing operation and if the weeds are not controlled then the decrement in productivity is also 50% or higher relying on the composition and intensity of weeds. Losses because of weeds differ among countries; relying on the major weed species and also their suppressing techniques followed by regional growers. Weeds are the main factor of biotic stress in the production of paddy in Srilanka which showed 30-40% losses in economic yield (Abeyskera and Anwudhika, 2001). The overall cultivated area of paddy in Bangladesh is about 105.0 lakh hectares with a production of 250.9 lakh tonnes where transplanted winter paddy alone occupies 55.6 lakh hectares of land with a production of 112.5 lakh tonnes (Anonymous, 2001). But the paddy productivity of Bangladesh is lesser than the productivity of other paddy growing countries due to the heavy infestation of weeds (Mamun, 1988). Weed infestation can even create problem in the operation of combine harvester and significantly enrich the costs of harvesting, threshing and drying. Contamination of weed seeds lowers the quality of paddy grains and ultimately the cash value of grains. The yield loss due to weed problem in paddy was observed about 15-66 per cent in direct-seeded paddy and 6-30 per cent in puddled transplanted paddy in India (Gharde et al., 2018). Popularization of integrative tactics of weed control with the application of herbicides by ensuring safe use is required to avoid ill impact on human health, environment and avoid weeds building resistance against herbicides (Rao et al., 2020). Location specific integrative weed management tactics can be developed based on weed ecology and biology and fine tuning of the accessible technologies to handle the weed problem with no harm (Rao et al., 2020).

The current experiment was performed during Kharif, 2019 and 2020 in the experimental farm of Uttar Banga Krishi Viswavidyalaya, Coochbehar, West Bengal, India. The soil of the experimental site was sandy loam textured and slightly acidic in reaction (soil pH 6.15). Soil organic carbon content was high (1.07%), medium available nitrogen (290.4 kg ha^-1), phosphorus (19.4 kg ha^-1) and potassium (118 kg ha^-1) was the initial fertility status of experimental soil. Paddy cultivar, Maudamani (CR Dhan 307) was taken in this experiment. The experiment was designed in randomized blocks with four replications and five treatments viz. pretilachlor @ 0.75 kg ha^-1 at 3 DAT with paddy weeder at 30 DAT (P₁), pyrazosulfuron ethyl @ 20 g ha^-1 at 3 DAT with metsulfuron methyl 10% WP + chlorimuron ethyl 10% WP (ready mix) @ 20 g ha^-1 at 25 DAT (P₂), bispyribac sodium @ 25 g ha^-1 at 15 DAT with paddy weeder at 30 DAT (P₃), complete weed free (P₄) and weedy check (P₅).

Plant samples were taken at 30 DAT, 60 DAT, 90 DAT and harvest in both of the years. The samples are taken using 1 m² quadrate whereas, weed samples were taken at 15 DAT, 30 DAT, 45 DAT and 60 DAT from five places using 1 m² quadrate. Weed samples were collected, oven dried at 65°C until constant sample weight observed and then dry weight was noted down.

B:C ratio and weed indices i.e., weed control efficiency and weed control index, weed persistence index and weed index were evaluated through the following formulas:

Data from both the years were calculated and made average for analysis. The data regarding weeds found from the samples were transformed using square root transformation (ÖX+0.5) for treatment comparison through ANOVA. Effect of the treatments was statistically compared by Fisher’s least significant difference method at 5% level of significance (Gomez and Gomez, 1984). All statistical analyses were completed by SPSS 24.0 software package created by IBM Corp. (2016).

This experiment revealed (Table 1) that growth attributes like height of plants and accumulation of dry matter at 60 and 90 DAT and at harvest were significantly influenced by the weed management treatments in rice. The treatment, bispyribac sodium @ 25 g ha^-1 at 15 DAT + paddy weeder at 30 DAT treatment (P₃) recorded the maximum plant height at harvest (117.62 cm) except the complete weed free treatment which had also significantly taller plants than all the chemical and integrative weed management treatments in both years. The paddy crop with complete weed free (P₄) treatment registered highest accumulation of dry matter (1288.40 g m^-2 at 90 DAT and 1531.80 g m^-2 at harvest) at 90 DAT and harvest which differed significantly with other treatments in both years. This was might be due to no competition of paddy with weeds during the later period of crop growth. This weed free treatment was closely followed by bispyribac sodium + paddy weeder treatment (P₃) at 90 DAT (1262.30 g m^-2) and harvest (1511.80 g m^-2). Adilakshmi et al. (2022) found that the treatment combination with bispyribac sodium showed better growth attributes of paddy. At 30 DAT, bispyribac sodium + paddy weeder treatment (P₃) achieved shortest plants and minimum dry matter accumulation due to some phytotoxic effect of bispyribac sodium though insignificant variation was found. Paddy crop under P₅ i.e., weedy check treatment recorded the shortest plants with lowest dry matter accumulation at all the stages of crop growth except 30 DAT. Paddy grown in complete weed free plots i.e., P₄ option registered the maximum number of tillers m^-2 (179.81 m^-2 at 30 DAT, 287.90 m^-2 at 60 DAT, 245.40 m^-2 at 90 DAT and 228.74 m^-2 at harvest) on all the dates of observation followed by bispyribac sodium + paddy weeder i.e., P₃ option (175.56 m^-2 at 30 DAT, 286.60 m^-2 at 60 DAT, 242.40 m^-2 at 90 DAT and 225.61 m^-2 at harvest) which varied significantly with other chemical and integrative weed management treatments. This was mainly due to lower crop-weed competition under these treatments than others.



Yield attributing characters (Table 2) such as number of panicles m^-2, number of filled grains panicle^-1 varied significantly under different weed management treatments for both the years. The treatment, completely weed free i.e., P4 noted down the maximum number of panicles m^-2 and number of filled grains panicle^-1 followed by bispyribac sodium + paddy weeder i.e., P₃ treatment and they were statistically at par. This was due to higher dry matter accumulation under these treatments than others during the later period of crop growth. Paddy crop under P₅ i.e., weedy check recorded the lowest number of panicles m^-2 as well as number of filled grains panicle^-1 due to maximum weed density during the crop growing period. The test weight was not significantly influenced by various weed controlling options.



Among weed management treatments, paddy crop under no weed i.e., P₄ treatment exhibited the maximum productivity of grains (6.68 t ha^-1) trailed by P₃ i.e., bispyribac sodium + paddy weeder treatment (6.54 t ha^-1) (Table 2). Crop remained under weedy check i.e., P₅ treatment noted down the minimum yield of grains (5.79 t ha^-1). The crop treated with pretilachlor @ 0.75 kg ha^-1 at 3 DAT + paddy weeder at 30 DAT i.e., P₁ the exhibited the highest straw yield (8.26 t ha^-1) followed by weed free i.e., P₄ (8.25 t ha^-1) and P₃ i.e., bispyribac sodium + paddy weeder treatment (8.19 t ha^-1). These three treatments had also been found statistically at par. Crop treated as weedy check i.e., P₅ recorded the lowest straw yield of paddy (7.91 t ha^-1) on pooled basis (Table 2). Maximum harvest index was recorded to weed free i.e., P₄ (45.06%) followed by P₃ i.e., bispyribac sodium + paddy weeder treatment (44.39%) and the lowest harvest index was recorded with weedy check treatment i.e., P₅ (42.29%).

The weed species were identified in both the years. From initial stage to 45 DAT, there was maximum number of broad-leaved weeds. The occurrence of grasses was thereafter 45 DAT. The Common broadleaved weeds were Ottelia alismoides, Sphenoclea zeylanica, Marsilea quadrifolia, Alternanthera sessilis. However, two types of grasses i.e., Panicum repens, Echinochloa crusgalli and one type of sedge i.e., Scirpus articulate were found.

The data presented in Table 3 revealed irrespective of different levels of weed control treatment, the first date of observation (15 DAT) regarding weed population did not appear in any categories of weeds might be due to preparation of weed free puddled beds with proper depth of water submergence.



The total weed population and weed dry weight were recorded under different weed management treatments on 30 DAT, 45 DAT and 60 DAT. Lowest weed population (0.71 m^-2 on all the dates) and weed dry weight (0.71 g m^-2 on all the dates) were recorded in completely weed free i.e., P₄ treatment followed by P₃ treatment i.e., bispyribac sodium + paddy weeder at all the dates of observation (weed population and weed biomass were 2.34 m^-2 and 2.95 g m^-2 at 30 DAT, 2.75 m^-2 and 3.94 g m^-2 at 45 DAT and 2.82 m^-2 and 3.88 g m^-2 at 60 DAT, respectively). Highest weed population and weed biomass were recorded in weedy check i.e., P5 treatment on all the dates.

The best efficiency in controlling weeds (WCE) and weed control index (WCI) were recorded (Table 4) in pooled data to those paddy crops which were treated with complete weed free treatment i.e., P₄ (100.00% in both WCE and WCI on all the dates) followed by P₃ i.e., bispyribac sodium + paddy weeder treatment (WCE was 76.48% at 30 DAT, 79.01% at 45 DAT and 80.79% at 60 DAT and WCI was 80.17% at 30 DAT, 72.30% at 45 DAT and 82.51% at 60 DAT) and the lowest weed control index and lowest efficiency in controlling weeds was obtained with the crop under weedy check i.e., P₅ on the different dates of observations (0.00% in both WCE and WCI at 30 DAT, 45 DAT and 60 DAT) as no weed control measures had been followed there. Maurya et al. (2023) reported that bispyribac sodium provided better result among the chemicals used in terms of efficient control of weeds.



Weed persistence index indicating relative gathering of dry matter of weeds in every count with compared to control, which confirmed the effectiveness of used herbicide (Table 5). This index indicated that pyrazosulfuron ethyl @ 20 g ha^-1 at 3 DAT followed by metsulfuron methyl 10% WP + chlorimuron ethyl 10% WP (ready mix) @ 20 g ha^-1 at 25 DAT (P2) treatment resulted in highest value of weed persistence index at 60 DAT (1.88) and 90 DAT (1.03) whereas, it was lowest at 30 DAT (0.93). This finding strengthened the fact that application of herbicides alone initially controlled the weeds but weed infestation was again reached to maximum during the later period of crop growth. Gupta et al. (2023) observed that the combination of other herbicide with pyrazosulfuron ethyl was capable to show lowest weed persistence index. However, complete weed free treatment (P₄) always recorded the lowest weed persistence index.



However, the lowest weed index recorded to those paddy plots which were considered as completely weed free (0.00%) followed by treated with bispyribac sodium @ 25 g ha^-1 at 15 DAT + paddy weeder at 30 DAT (2.10%) and the highest weed index was recorded in un-weeded control (13.32%) plots (Table 5).

The above table (Table 6) showed that the highest gross return was recorded in completely weed free i.e., P₄ treatment (₹ 116700 ha^-1) followed by bispyribac sodium + paddy weeder i.e., P₃ treatment (₹ 114480 ha^-1) whereas, the highest net return was obtained from bispyribac sodium + paddy weeder i.e., P₃ treatment (₹ 59269 ha^-1). However, there were no crop-weed competition and results related to crop growth and yield were found best in completely weed free treatment (P₄), but the profit was reduced due to higher cost of cultivation in case of P₄ than others. Highest benefit-cost ratio was also obtained in bispyribac sodium @ 25 g ha^-1 at 15 DAT + paddy weeder at 30 DAT i.e., P₃ treatment (2.07). Proportionately higher yield with respect to cost of cultivation was obtained in the treatment, bispyribac sodium + paddy weeder (P₃) as compared to other treatments. Swain et al. (2023) discovered that the application of bispyribac sodium provided maximum net return from paddy among the chemical weed control options.

Following the above results, it might be concluded that combination of mechanical and chemical weed management had direct effect on reducing weed infestation, increasing crop productivity and economic return. Thus, application of bispyribac sodium @ 25 g ha^-1 at 15 DAT + paddy weeder operation at 30 DAT could be recommended for rice farmers during kharif season to achieve highest yield and profit as well as best weed control in terai region of West Bengal.

The data presented in this research paper was taken from Ph.D. research work of Pratonu Bandyopadhyay, Uttar Banga Krishi Viswavidyalaya, Pundibari, Coochbehar in kharif season of 2019 and 2020. The financial support received from Uttar Banga Krishi Viswavidyalaya has also been acknowledged.

This research is conducted ethically and in compliance with relevant guidelines and regulations. We, all the authors have declared that no conflict of interest exists that could have appeared to influence the work reported in this paper.