Performance of Various Weed Management Approaches on Weed Dynamics, Yield Attributes and Yield of Puddled Rice under Different Planting Techniques

Rice is the most significant staple food crop for more than half of the world’s population, particularly in densely populated areas experiencing fast expansion. In irrigated lowland rice, transplanting is the most common and traditional establishment technique. Increasing water scarcity is becoming a severe danger to rice cultivation. Thus, it is necessary to create water-saving technology that simultaneously preserves soil sustainability and health while still being profitable (Hugar et al., 2010).

Drum-seeded rice under puddled conditions has significant relevance in modern production systems since it saves time, labour, energy and profitability while increasing cropping intensity by lowering turnaround time and avoiding onerous activities like nursery preparation and hand transplanting. Across the world, especially in India, the SRI cultivation technique is gradually gaining popularity. In comparison to the traditional technique of farming in India, the SRI is a methodology to boost rice output by altering microclimate and soil conditions and also minimises the usage of inputs like water and labour (Mohanty et al., 2014).

In agroecosystems, weeds are the main factor in low productivity and financial loss. Weeds also extrude chemicals from their roots and leaves that are harmful to plant crops, interfering with normal crop growth and resulting in a drop in yield and quality (Vikram sai et al., 2022). Chemical weed management is increasingly popular and is the ideal alternative to manual weeding since hand weeding is labour-intensive, tedious, time-consuming and impracticable in adverse weather. Using herbicides was the more appealing choice as the operation would be finished in one application and save time. Moreover, it broadens the range of weed control in a single application, lowers the cost of treatment and minimizes herbicide damage and consumption rate to crops (Guru et al., 2020).

In this light, the current study was conducted to assess “The performance of various weed management approaches on weed dynamics and yield of puddled rice under different planting techniques.”

A field experiment was conducted in experimental farm of Faculty of Agriculture, Annamalai University during the Navarai season of 2021 which is located at a latitude of 11°24‵N, longitude of 79°44‵E and at an altitude ± 5.79 MSL. The climate of the experimental area is humid tropic, with an average rainfall of 1248 mm and maximum and minimum temperatures recorded during the planting season were 22.6°C and 32.3°C, respectively. The experiment has been laid out in split plot design which consists of two planting techniques - drum seeded rice, system of rice intensification (SRI) in  main plot and eight weed management approaches - weedy check, Hand weeding twice, Cono weeding thrice, Pretilachlor @ 0.5 kg a.i ha-1 fb Cono weeding on 30 DAS/DAT, Fenoxaprop - p - ethyl @ 56.60 g a.i ha^-1 fb Cono weeding on 40 DAS/DAT, Bispyribac sodium @ 20 g a.i ha^-1 fb Cono weeding on 40 DAS/DAT, Pretilachlor @ 0.5 kg a.i ha^-1 fb Fenoxaprop - p - ethyl @ 56.60 g a.i ha^-1, Pretilachlor @ 0.5 kg a.i ha^-1 fb Bispyribac sodium @ 20 g a.i ha^-1 in sub plot and was replicated thrice. ADT 43 variety was used as test crop.

In drum seeding, germinated seeds were planted using a manually operated rice drum seeder with a spacing of 20 × 10 cm. In SRI, 14-day-old seedlings were manually transplanted with a spacing of 25 × 25 cm @ 2 seedlings hill^-1.

Hand weeding was done twice, once on 20 DAS/DAT and second on 40 DAS/DAT. Conoweeding was done thrice at 10 days interval starting from 20, 30 and 40 DAS/DAT. Pretilachlor was applied as pre-emergence on 8 DAS in drum seeding and 3 DAT in SRI method of planting while both Fenoxaprop - p - ethyl @ 56.38 g ha^-1 and Bispyribac sodium @ 20 g ha^-1 as a post-emergence herbicide with 500 l of water ha^-1 were applied on 20 DAS/DAT. The observations on weed density and weed control efficiency were recorded on 30DAS/DAT and 60DAS/DAT. Yield parameters were taken from five randomly selected places using 1 m² quadrant from net plot area. Square root of transformation was done for weed density by using the formula , the data relating to weed control efficiency was transformed by arc sin transformation. All the observations recorded in the experiment were statistically analysed by AGRES software.
 

Data regarding cultural energy used through various inputs was computed and energetics were worked out as suggested by Mittal et al., 1985. The energy equivalents used for different inputs and outputs were mentioned in Table 1.


 
Energy use efficiency (EUE)
 

 
Energy productivity
 

 

 
Energy profitability
 

 
Specific energy

 

Weed flora of the experiment site
 
The prominent weeds appeared in the experimental field at all stages of observation were Echinochloa colona, Echinochloa crusgali, Leptochloa chinensis among grasses and in sedges viz., Cyperus diffoirmis, Cyperus iria, Cyperus rotundus and among broad leaved weeds viz., Eclipta alba, Sphenoclea zelyancia, Bergia capensis and Marsilea quadrifolia.
 
Weed density and dry weight
 
Weed density and dry weight was considerably influenced by different weed management approaches and planting techniques (Table 2). Among the planting techniques, the SRI method of planting recorded the lowest weed density (29.90 and 60.45 no.m^-2) and weed dry weight (26.47 and 5313 g m^-2) on both 30 and 60 DAT. This might be attributed to SRI resulting in decreased weed density owing to puddling, which buries weeds into the deeper layer of the mud where anaerobic activity can degrade them, resulting in less emergence of deeply planted weed seeds (Kumar et al., 2021).



Irrespective of the weed management approaches evaluated, the combined application of pretilachlor @ 0.5 kg a.i ha^-1 fb bispyribac sodium @ 20 g a.i ha^-1 as resulted in the lower weed density (10.03 and 25.91 no m^-2) and dry weight (8.76 and 22.11 g m^-2). This might be attributed to pretilachlor, as PE is particularly effective on grasses and sedges. When sprayed, it penetrates predominantly by the sprouting shoots and secondly through the roots, with translocation throughout the plant resulting in the impact on weed seed at early stages. Since bispyribac sodium is an ALS (acetolactate synthase) inhibitor, it interferes with producing a plant enzyme necessary for growth. It reduces plant amino acid synthesis, resulting in weed control at a later stage of the crop. These results were in concordance with (Surayakala et al., 2019).
 
Weed control efficiency
 
The findings in Table 2 reveal that among the planting techniques followed, the highest weed control efficiency was registered by SRI method of planting (69.96 and 67.04 on 30 and 60 DAT). This might be because the smothering effect of rice seedlings on developing weeds resulted in minimal weed emergence. These findings are in agreement with those of (Hassan et al., 2010).

The consecutive application of pretilachlor @ 0.5 kg a.i ha^-1 fb bispyribac sodium @ 20 g a.i ha^-1 recorded highest weed control efficiency (90.26 and 86.09 at 30 and 60 DAS/DAT).This might be owing to the persistence of pretilachlor fb bispyribac sodium, which could have considerably helped to control the weeds for longer period. Pretilachlor was reported to have a half-life period of 7.52-9.58 days (Kaur et al., 2015) and bispyribac sodium is comparatively more persistent with a half-life of 9.93 days (Ramprakash et al., 2015) and persists up to 42-115 days (Singh and Singh, 2015) in soil and may have delivered the highest weed control efficiency. These findings were in agreement with the findings of (Chinnamani et al., 2018 and Rathika and Ramesh, 2018).
 
Yield attributes and yield
 
The data in Table 3 shows that in terms planting techniques evaluated, the SRI technique of transplanting produced higher productive tillers m^-2 (309.70) and filled grains panicle^-1 (91.25). This might be because seedlings were transplanted earlier, allowing for extra tillering and roots. In addition, larger spacing in a square pattern allowed for increased canopy and root growth and subsequent grain filling. These findings are concurrence with those of (Nazir et al., 2020; Sai et al., 2022).



The yield attributes were significantly altered by weed management practices (Table 3). However, the application of pretilachlor @ 0.5 kg a.i ha^-1 fb bispyribac sodium @ 20 g a.i ha^-1 registered higher productive tillers m^-2 (359.24) and filled grains panicle^-1 (100). This might be because early weed control with PE herbicides favoured strong crop development, followed by later PoE herbicide treatment of emerging weeds, decreased competition, enhanced the capacity of source and sink and resulted in higher yield characteristics. This was in accordance with the results of (Kuotosu and Singh, 2020).

The highest grain yield was registered by SRI method of planting (5.01 t ha^-1). This is most likely due to the massive root volume, profuse and vigorous tillers with longer and more panicles with higher grain weight, all of which contributed to increased grain yield. These findings agree with those of Kumar et al., (2015); Nath and Dev (2018) and Kuotsu and Singh (2020).

The grain yield was substantially affected by different weed management approaches. Among the weed management approaches tested, the application of pretilachlor @ 0.5 kg a.i ha^-1 fb bispyribac sodium @ 20 g a.i ha^-1 (5.98 t ha^-1) was the most effective approach. This could be due to the sequential application of pretilachlor @ 0.5 kg a.i ha^-1 as a PE herbicide, which effectively controlled the weeds during the germination phase and bispyribac sodium @ 20 g a.i ha^-1 as a PoE, which further reduced the late germinating weeds, resulting in an increase in plant biomass and productive tillers, resulting in the highest grain yield. These are congruent with the findings of (Bhattacharya et al., 2022, Kumaran et al., 2013 and Walia et al., 2012).
 
Energetics
 
The data regarding the energy use efficiency and profitability was furnished in Table 4. Among the planting techniques evaluated the highest energy use efficiency (13.96 MJ ha^-1), profitability (12.96 MJ ha^-1) and energy productivity (0.40 kg MJ^-1) was found in the SRI method of planting along with PE application of pretilachlor @ 0.5 kg a.i ha^-1 fb bispyribac sodium @ 20 g a.i ha^-1. It might be due to the high output energy generation in the SRI technique. However, in both planting techniques and weed management practices the lowest specific energy was registered by SRI planting (2.63 MJ kg^-1) and pretilachlor @ 0.5 g a.i ha^-1 fb PoE application of bispyribac sodium @ 20 g a.i ha^-1 (2.08 MJ kg^-1) due to higher grain yield.



Irrespective weed management practices tested, highest energy use efficiency, profitability and energy productivity was registered by the sequential application of PE pretilachlor @ 0.5 kg a.i ha^-1 fb PoE application of bispyribac sodium @ 20 g a.i ha^-1 (16.62, 15.62 MJ ha^-1 and 0.48 kg MJ^-1, respectively). This might be attributed to more incredible output energy by reducing weed competition and improving crop production.
 
Linear relationship
 
Fig 1 depicts that in Navarai, 2021 the linear association between total weed density and grain yield was strongly and negatively correlated (r = -0.931). The study found that weed interference contributed to the negative influence on crop yield attributes, which reduced the yield in both SRI and drum-seeded rice, with uncontrolled weeds causing over 52.51 and 53.56% yield reduction in both the planting techniques.

The results of the field experimentation concluded that the SRI strategy of planting, along with the application of PE pretilachlor @ 0.5 kg ha-1 fb PoE bispyribac sodium @ 20 g ha^-1 reduced the infestation of dominant weed species and these practises could be suggested as an efficient, economically viable, ecologically desirable and practically feasible management system for controlling weed species in the puddled rice wetland ecosystem.

All authors declare that they have no conflicts of interest.