Sustainable weed management approaches for cultivation of upland rice under Tripura condition

Introduction

In India, rice is primarily cultivated as puddle-transplanted rice, either under irrigated or rainfed conditions. This method of cultivation is characterized by its high demand for labor and energy. The traditional practice of transplanting after puddling significantly impacts the physical properties of the soil, leading to the disruption of soil aggregates, decreased permeability in subsurface layers, and the formation of a hard pan at shallow depths. These changes complicate land preparation and necessitate greater energy expenditure to achieve suitable soil tilth for subsequent crops. Additionally, the rising labor costs in India are diminishing the profitability of puddle-transplanted rice. Furthermore, this cultivation method is not environmentally sustainable, as it contributes to substantial methane emissions from lowland rice fields. To address these challenges, transitioning to direct-seeded rice cultivation emerges as a viable alternative. Direct seeded rice (DSR) represents a cost-efficient method for establishing rice crops, wherein dry seeds are directly sown into unpuddled soil. This technique offers significant advantages, including a reduction in irrigation water usage by 12-35%, a decrease in labor requirements by up to 60%, and the potential for higher net returns while achieving yields comparable to those of transplanted rice (Kumar and Ladha, 2011) [7] . Furthermore, DSR is characterized by a shorter growth duration, lower labor requirement, reduced water consumption (Bhushan et al., 2007) [8] , and diminished methane emissions (Wassmann et al., 2004) [10] . However, despite its numerous advantages, the issue of weed management poses a significant challenge to the successful implementation of dry direct seeded rice in South Asia (Kumar and Ladha, 2011; Rao et al., 2007; Singh et al., 2008) [7,11,14] . Controlling weeds in dry DSR is more complex than in conventional tillage-transplanted rice (CT-TPR), as weeds tend to emerge simultaneously with the rice seedlings in dry DSR, which are less competitive compared to the 30-35 day old seedlings used in CT-TPR. Additionally, the initial flooding employed in CT-TPR helps in weed suppression, a benefit that is absent in dry DSR (Kumar and Ladha, 2011) [7] . In light of these challenges, a weed management package has been developed for upland rice to evaluate the effectiveness of various weed control practices under the conditions prevalent in Tripura.

Materials and Methods

The field experiment was carried out in the villages of South Tripura district during the kharif seasons of 2013-2014 and 2014-2015 to investigate the impact of various weed management practices on direct seeded upland rice under the conditions prevalent in Tripura. The agricultural farm is located at approximately 22°57' to 23°45' N latitude and 91°19' to 91°53' E longitude, with an average elevation of 120 meters above sea level. This farm is situated within the Mid Tropical Plain zone (NEH-6) of Tripura. The experimental site lies in the semi-arid and sub-humid lateritic belt of the South Tripura District. The soil in the experimental field is characterized as sandy loam, exhibiting low fertility and an acidic reaction. During the crop growing period from June 2013 to March 2014, the average maximum and minimum temperatures ranged from 25.2°C to 34.2°C and 10.1°C to 25.3°C, respectively, in the first year, while in the second year, they ranged from 25.8°C to 35.9°C and 12.2°C to 25.4°C. Additionally, fluctuations in relative humidity were noted during the cropping seasons of 2013-14 and 2014-15, with values ranging from 55% to 86% in 2013-14 and from 72% to 90% in 2014-15. The South-West monsoon typically begins in South Tripura around mid-June and lasts upto October, often accompanied by intermittent dry spells. Over 80% of the total annual rainfall occurs during the monsoon months (June to September). The total rainfall recorded during the rice growing season was 1156.1 mm in 2013 and 1461.8 mm in 2014. The field experiment was conducted using a randomized block design that included twelve treatments and three replications. Different treatments were pendimethalin @ 1.0 kg ha-1 at 2 DAS, bispyribac sodium @ 25 g ha-1 at 25 DAS, pendimethalin @ 1.0 kg ha-1 at 2 DAS+ one hand weeding at 30 DAS, pendimethalin @ 1.0 kg ha-1 at 2 DAS + bispyribac sodium @ 25 g ha-1 at 20 DAS, metsulfuron methyl+ chlorimuron ethyl (Almix) @ 4 g at 10 DAS followed by bispyribac sodium @ 25 g at 20 DAS, pyrazosulfuron ethyl @ 25 g ha-1 at 3 DAS followed by bispyribac sodium @ 25 g at 20 DAS, fenoxapropp-ethyl @ 60 g ha-1 + metsulfuron methyl + chlorimuron ethyl (Almix) @ 4 g ha-1 at 15 DAS, stale seed bed + smother crop (cowpea) in between two rows of rice, stale seed bed + one hand weeding at 30 DAS, sesbania (broadcast) @ 25 kg ha-1 during sowing of rice + 2,4-D @ 500 g ha-1 at 25 DAS, hand weeding at 15, 30 and 45 DAS, weedy check were assigned in a randomized block design replicated thrice. Rice variety NDR-97 was used for the experimental purpose. The upland rice was fertilized as per recommended package of practices in Tripura. Five tonnes of Farm Yard Manure were applied at the time of field preparation for both the crop. Chemical fertilizers were applied to meet 60 kg nitrogen in the form of urea, 40 kg phosphorus in the form of single superphosphate and 40 kg potassium in the form of muriate of potash in the rice. Weed assessments were conducted at various growth stages (15, 30, 60 days, and at harvest) by randomly placing quadrats across three locations within each plot to determine the average weed count. Samples collected from each quadrat were categorized into grasses, broad-leaved weeds, and sedges, then dried and weighed. The dry matter of weeds was reported in grams per square meter for each category. Additionally, data regarding growth parameters, yield attributes, and overall rice yield were recorded. The economic analysis of various weed management strategies was also performed (AF Akinsola, 2022) [12] . The experimental data pertaining to each characteristic of crops and weeds were subjected to statistical analysis using the technique of "Analysis of Variance." The significance of the results was evaluated through the variance ratio, specifically at the 5% level of significance, as outlined by Gomez and Gomez (2010) [5] . The tables include the standard error of means (S.Em.±), the critical differences (C.D.) for comparing mean differences, and the coefficient of variability (C.V.).

Results and Discussion

Weed flora and dryweight of weeds

The prevalent weed species identified in the experimental field included Amaranthus viridis, Hedyotis corymbosa, Spilanthes acmella, Ludwigia parviflora, Cleome rutidosperma, and Malvestrum coromondalianeum among the broadleaf weeds, Digitaria sanguinalis among the grasses, and Cyperus iria among the sedges. A similar composition of weed flora in directseeded rice has been documented by Duary et al. (2005) [2] , Duary and Mukherjee (2013) [3] , and Duary et al. (2016) [4] . The impact of various weed management strategies on the dry weight of grasses, broadleaf weeds, sedges, and total weed biomass exhibited highly significant differences at 60 days after seeding, as presented in Table 1. There were no significant changes observed in the dry weight of grasses, broadleaved plants, sedges, and total weeds over the two-year period. The data clearly indicates that, in both years, the dry weight of weeds, including grasses, broadleaved, sedges, and total weeds, was highest in the weedy check (T12) compared to the other treatments evaluated (Table 1). The lowest dry weight was noted in the treatment involving hand weeding conducted three times at 15, 30, and 45 days after sowing (DAS) (T11), which was closely followed by the treatments of pendimethalin combined with one hand weeding (T3) and pendimethalin combined with bispyribac sodium (T4). These results align with the findings reported by Duary et al.

(2005) [2] and Bhurer et al. (2013) [1] .

Effect of weed management practices on yield and economics

Yield and economics of rice as affected by different weed management practices are given in Table 2. Return rupee -1 invested 1 st year 2 nd year 1 st year 2 nd year 1 st year 2 nd year 1 st year 2 nd year Pendimethalin @ 1.0 kg ha - The data presented in Table 2 clearly indicated that various weed management practices positively influenced the yield and economics of upland rice. Among the treatments evaluated, the method of hand weeding conducted three times at 15, 30, and 45 days after sowing (T 11 ) achieved the highest grain and straw yields over both years. This approach was comparable to the treatments involving pendimethalin combined with one hand weeding (T 3 ) and pendimethalin paired with bispyribac sodium (T 4 ). The effective and timely implementation of weed management strategies in these treatments led to a reduction in weed dry weight, thereby providing the crop with adequate space, light, nutrients, and moisture, ultimately resulting in increased grain and straw yields.

The findings of the current study indicated that the profitability from rice cultivation was significantly influenced by the weed management strategies implemented. The combination of pendimethalin at a rate of 1.0 kg ha -1 applied at 2 days after sowing (DAS) along with bispyribac sodium at 25 g ha -1 applied at 20 DAS (T 4 ) yielded the highest net returns, amounting to Rs. 23847/-in the first year and Rs. 26010/-in the second year, as well as the best return per rupee invested (2.02 and 2.11) across both years, establishing it as the most profitable weed management approach. The treatment involving pendimethalin @ 1.0 kg ha -1 combined with one hand weeding at 30 DAS (T 3 ) produced net returns of Rs. 21427/-and Rs. 25573/-in the first and second years, respectively, making it the second most effective treatment. This success can be attributed to the higher grain and straw yields achieved with these methods. A similar conclusion was drawn by Yakadri et al. in 2016 [15] . Although the highest rice yield and gross returns were observed with hand weeding at 15, 30, and 45 DAS (T 11 ), the analysis of net income and return per rupee invested indicated that this method was less profitable compared to the treatments involving pendimethalin at 1.0 kg ha -1 at 2 DAS combined with bispyribac sodium @25 g ha -1 at 20 DAS (T 4 ) and pendimethalin at 1.0 kg ha -1 with one manual weeding at 30 DAS (T 3 ). This suggests that conducting three hand weedings throughout the crop's growth period may be economically unfeasible and unnecessary. The net income was negative in the weedy check treatment due to increased competition between rice and weeds, which adversely affected crop growth and resulted in lower grain and straw yields. This further underscores the critical role of effective weed management in achieving profitable rice production. This aligns with the findings of Prashanth et al. in 2016, [9] who noted that the lowest net returns and benefit-cost ratio were associated with the unweeded check in rice. Additionally, Kashid et al. in 2015 [6] reported that the highest net returns and return per rupee invested were achieved through the pre-emergence application of herbicides in conjunction with one hand.

Conclusion

A cropping system that is economically sustainable is generally embraced by farmers. The current study demonstrated that the growth and yield of direct-seeded upland rice were significantly affected by various weed management strategies. Among the treatments evaluated, the combination of pendimethalin and bispyribac sodium (T4) yielded the highest net returns and the best return on investment, establishing it as the most profitable weed management approach for direct-seeded aerobic rice in the upland conditions of Tripura.

References

1. Bhurer KP, Yadav DN, Ladha JK, Thapa RB, Pandey KR. Efficacy of various herbicides to control weeds in dry direct seeded rice (Oryza sativa L.). Glob J Biol Agric Health Sci. 2013;2(4):205-12.
2. Duar B, Mondal DC, Hossain A. Integrated weed management in direct seeded dry sown rice in lateritic belt of West Bengal. Indian J Weed Sci. 2005;37(1/2):101-2.
3. Duary B, Mukherjee A. Distribution pattern of predominant weeds of wet season and their management in West Bengal, India. In: Proceedings 24 th Asian-Pacific Weed Science Society Conference, October 22-25, 2013. Bandung, Indonesia. p.191-9.
4. Duary B, Kumar M, Teja KC, Dash S. Weed management in dry direct seeded rice through integrated approaches. In: Proceedings of 4th International Agronomy Congress, New Delhi, India, Nov 22-26, 2016. Extended Summaries Vol. 1:277-8.
5. Gomez KA, Gomez AA. Statistical procedures for agricultural research. New Delhi: Wiley India Pvt. Ltd.; 2010.
6. Kashid NV, Barhate KK, Bodake PS. Management of weeds in direct seeded rice. Indian J Weed Sci. 2015;47(2):110-2.
7. Kumar V, Ladha JK. Direct seeding of rice: recent developments and future research needs. Adv Agron. 2011;111:299-360.
8. Ladha JK, Gupta RK, Singh S, Tirol-Padre A, Saharawat YS, Gathal M, et al. Saving of water and labor in a ricewheat system with no-tillage and direct seeding technologies. Agron J. 2007;99:1288-96.
9. Prashanth R, Kalyana Murthy KN, Madhu Kumar V, Murali M, Sunil CM. Bispyribac sodium influence on nutrient uptake by weeds and transplanted rice. Indian J Weed Sci. 2016;48(2):217-9.
10. Wassmann R, Neue HU, Ladha JK, Aulakh MS. Mitigating greenhouse gas emissions from rice-wheat cropping systems in Asia. Environ Dev Sustain. 2004;6:65-90.
11. Rao AN, Johnson DE, Sivaprasad B, Ladha JK, Mortimer AM. Weed management in direct-seeded rice. Adv Agron. 2007;93:153-255.
12. AF Akinsola and AG Oluwafemi. Phytochemical analysis, proximate composition and mineral profile of Cleome rutidosperma found in Ado-Ekiti, Nigeria. Int. J. Adv. Biochem. Res. 2022;6(2):94-100. DOI: 10.33545/26174693.2022.v6.i2b.141
13. Sharma SK, Pandey DK, Ganagwar KS, Tomar OK. Weed control in direct, dry-seeded rice in India: comparison of seedbed preparation and use of pendimethalin. Int Rice Res Notes. 2004;29(2):30-31.
14. Singh G, Singh OP, Kumar V, Kumar T. Effect of methods of establishment and tillage practices on the productivity of rice (Oryza sativa)-wheat (Triticum aestivum) cropping system. Indian J Agric Sci. 2008;78:163-6.
15. Yakadri M, Madhavi M, Ramprakash T, Leela R. Herbicide combinations for control of complex weed flora in transplanted rice. Indian J Weed Sci. 2016;48(2):155-157.