Pre and Post Emergence Herbicides Influence on Productivity of Transplanted Rice

Rice is one of the most important staple food crops in the world, providing nutrition to more than half of the global population. In India, rice occupies an area of 45.07 million hectares, 122.27 million tonnes production and 2713 kg/ha productivity (GoO, 2021). In Odisha, rice is cultivated in 4.03 million ha during Kharif and rabi/summer seasons with a production of 8.73 million tons and productivity of 2173 kg ha^-1 (GoO, 2021). Reddy et al., (2003) from Hyderabad reported that the transplanted rice yield was reduced by 28-40% as a result of Cyperus spp., Paspalum spp., Caesulia axillaris, Rotala densiflora and Monocharia vaginalis.
       
The use of herbicides in agriculture has revolutionized weed management practices, significantly impacting crop productivity and overall agricultural sustainability (Bhattacharya  et al., 2022). Uncontrolled weed growth reported to reduce rice yield by 33 to 45% (Manhas et al., 2012). Manual weeding in rice becomes difficult because labor scarcity (at specific time) as well as time consuming and costly (Singh et al., 2012; Sanodiya and Singh, 2022). On the other hand, the weed control through herbicides is less costly and easy to apply more effectively.
       
Pre-emergence herbicides play a pivotal role in preventing weed establishment and competition with the transplanted rice. On the other hand, post-emergence herbicides are applied after both the crop transplanted and weed seedlings have emerged and these herbicides provide targeted control of established weeds that might have escaped pre-emergence treatments. However, a balanced and integrated approach to weed management is essential to ensure the long-term sustainability of agricultural practices while minimizing potential negative impacts on the environment and weed resistance development.

A field experiment on the “Effect of pre and post emergence herbicides on weed dynamics and productivity of transplanted rice in south Odisha” was conducted at the Post Graduate Research farm, M.S. Swaminathan School of Agriculture, CUTM, Paralakhemundi, Odisha during the kharif season of 2023. The location is situated at 23^o39'N latitude, 87^o42' E longitude with an altitude of 64 m above the mean sea level under typical sub-humid and sub-tropical climatic conditions. The experimental soil is sandy loam in nature having a pH of 6.27, organic carbon 0.4%, available N 115.40 kg ha-¹, available P 312 kg ha-¹ and available K 530.73 kg ha-¹. The average annual rainfall of this area is 1400 mm and this region comes under a sub-tropical region with high humidity climatic conditions. The total rainfall received during the cropping season, August to November 2023, was 459 mm. The weather during the crop growth period indicates that the maximum temperature varied from 35.1^oC to 29.7^oC and the minimum temperature ranged from 18.6^oC to 26.5^oC. The minimum wind speed was 3.3 km/h, while the maximum wind speed observed during crop growth was 5.9 km/h. The bright sunshine hours ranged from 4.8 h/day to 11.0 h/day.
       
The weed management treatments consisting of fourteen combinations of pre and post emergence herbicides along with hand weeding and weedy check were tried in three replications (Table 1).


       
Transplanting of 35-day-old seedlings of RNR 15048 having a 125-day duration was done manually at a spacing of 20 cm ´ 15 cm in the third week of August 2023. To maintain uniform plant population, gap filling was done at 10 days after transplanting. The crop was irrigated as and when required to keep the land under saturated condition. Irrigation was given by flooding method.
       
A recommended dose of N, P₂O₅  and K₂O (100:60:60 kg/ha) were applied through urea, single super phosphate (SSP) and muriate of potash (MOP). Half dose of nitrogen and full doses of phosphorus and potassium were applied before transplanting as basal application. The remaining 50 percent of N was top dressed in two equal splits at active tillering (20 DAT) and panicle initiation (40 DAT) stages.
       
The observations on weeds (weed density, weed dry matter), crop (plant height, tiller number, crop dry matter, yield attributes) were recorded by adopting standard procedures. The crop was harvested at maturity and the grain yield was recorded at 14% moisture. The statistical analysis of the data was carried out as per the standard procedure for analysis of variance as described by Panse and Sukhatme (1954).

Weeds
 
The major grassy weeds observed  were Echinochloa colona, E. crusgalli, Leptochloa chinensis; broad leaved weeds were Caesulia axillaris, Alternanthera sessilis, Ammania baccifera  and Cyperus rotundus, C. iria, C. difformis  and Fimbristylis miliaceae among sedges.
       
When Compared to all  other treatments, hand weeding twice at  25  and  45 DAT  resulted  in a considerably lower total weed density at 30 DAT. The weed density observed in T₁₂, T₈ and T₅ are comparable with each other and significantly lower over T₁, T₂, T₃, T₄, T₇ and T₁₁.
       
At 30 DAT, T₁₃ treatment recorded significantly lower weed dry weight as compared to T₈ which in turn recorded lower dry weight over all other treatments. Significantly, higher weed dry weight was observed in weedy check over all other treatments.
       
At 30 DAS, the weed control efficiency was higher in treatment T₁₃ followed by T₈  and T₁₂ where the efficiency was more than 90%. On the other hand, it was between 80 to 90% in treatment T₉, T₁₀ and T₁₁ it was 79% in T₅.
       
The weed index was higher under T₁₄ (43.9%) followed by T₄, T₃ and T₂ which ranged between 28.5% to 29.5 %.

Crop
 
The plant height at 30 and 60 DAT and harvest did not vary significantly among different weed control treatments. The plant height ranged from 80 to 86 cm, 116 to 130 cm and 119 to 133 cm at 30 and 60 DAT and harvest respectively.
       
At 60 DAT, dry matter recorded under T₁₃ was comparable with T₈, T₉, T₁₀, T₁₁, T₃ and T₅ and significantly higher over all other treatments (Table 2).


       
Significantly, higher number of panicles were observed with T₁₃ as compared to T₂, T₃, T₄ and T₁₄ and comparable with other treatments (Table 2).
       
The number of spikelets per panicle observed with T₁₃  was comparable with that of T₄, T₅, T₆, T₇, T₈, T₉, T₁₀, T₁₁ and significantly superior over that of T₁, T₂, T₃, T₁₂ and T₁₄ (Table 2).
       
The grain yield observed with T₁₃ was at par with that of T₇ and T₁₀ and significantly superior over all other treatments. The increase in yield observed in T₁₃ over other treatments ranged from 23 to 42% under herbicide applied plots (Table 3).


       
The straw yield differed significantly among weed control treatments (Table 3). The straw yield observed in T₁₃ was at par with T₈, T₁₀, T₉ and T₇ and significantly superior over all other treatments.
       
The biological yield differed significantly by weed (Table 3). The biological yield in T₁₃ was at par T₇, T₈ and T₁₀ and significantly superior over all the other treatments.
       
Under hand weeding twice treatment there was 92% decrease in weed intensity and 76% in weed dry matter content. There was negative correlation between grain yield and weed intensity and weed dry matter (Table 4). Due to lower weed competition in hand weeded plot as compared to other herbicide applied plots there was increase in yield under T₁₃ (9 to 42%). Further, the panicle number, panicle length, grain number per panicle were significantly greater under hand weeding twice treatment as compared to other treatments (Table 1). More over these parameters had positive correlation with grain yield (Table 3) indicating that the improvement in these yield attributes under hand weeding improved the grain yield. Further, there was also improvement in dry matter production at 30 and 60 DAT and harvest in hand weeded plot over other treatments (Table 1). The dry matter improvement at vegetative stage increases the yield attributing characters and there by grain yield. Dry matter at 30 and 60 DAT had positive correlation with grain yield. Further, the harvest index was also higher in hand weeding as compared to other treatments. In several experiments, it has been observed that hand weeding gives better weed control and higher grain yield (Menon et al., 2016).


       
The harvest index was comparable in T₁ (40.49%) and T13 (40%) though the grain yield was significantly lower in former treatment than T₁₃ due to proportionate increase in dry matter to that of grain yield. The harvest index in Hand weeding indicates that the lower weed intensity and weed growth in hand weeding resulted in higher biological yield proportionate to that of grain yield. The lowest harvest index was observed in Weedy check (32.72%) due to biological yield in proportion to grain yield (Table 2).
       
In the present study, the grain yield obtained with T₁₀ was comparable with all other treatments and significantly superior over Weedy check due to lower weed intensity and weed dry matter which helped in increased  yield attributes and thereby grain yield in the former treatment. Deivasigamani (2016) reported that the herbicides applied 15 days after planting, triafamone (225 g/ml/ha) and triafamone + ethoxysulfuron (200 g/ml/ha and 225 g/ml/ha), showed  zero  weed  counts  of individual species,  such as grasses, sedges and broad l eaf weeds, as well  as weeddry  matter production and weed control index favoring higher grain yield.
       
Triafamone combined  with ethoxy  sulfuron  was  shown to have  the  highest  grain  yield,  the  lowest  weed dry  matter  generation and the most effective weed control (Menon et al., 2020) and also application of pyriftalid + bensulfuron methyl @ 450 ml ha^-1 at 9 DAT (Mondal et al., 2020). 
       
The grain yield observed with T8 was significantly superior over T₂, T₃, T₄ and T₁₄ and comparable with that of all other herbicide treated plots (Table 3). In the former treatments there was greater weed density, weed dry weight as compared to all other herbicide treatments. This helped in higher dry matter production of rice crop due to the higher tillering (Table 2). As a result of its higher tillering, the treatment T8 resulted higher number of panicles, accumulated more dry mass there by higher yield attributes like panicle length and grains per panicle (Table 2).  The increase of yield attributes has resulted increased yield in with T8 over latter treatments. The reports indicate that Pyrazosulfuron-ethyl at 42.0 g/ha applied at 3 DAT alone was most effective in managing associated weed species and yielded maximum grain yield of rice with lower weed index as compared to weedy check (Pal et al., 2012). The highest rice grain yield was recorded in application of Pyrazosulfuron ethyl 70% WDG @ 30 g ha^-1 as post emergence  (Raju et al., 2020).
       
T₂, T₃ and T₄ recorded  2727and 26% higher  yield over weedy check. The lower yield in the weedy check was due to higher weed growth and intensity, lower rice plant height, dry matter accumulation at different stages there by lower yield attributes in these treatments and ultimately less yield as compared to the former herbicide treatments. It has been reported the under transplanted conditions higher doses of penoxsulam 25.0 g/ha and 22.5 g/ha recorded significantly higher grain yield over unweeded control (Sasna  et al., 2016, Singh et al., 2009). Further, application of Bispyribac Sodium 10% SC @ 20 g a.i. ha^-1 kept the weed density and dry weight bellow the economic threshold level and increased the grain yield in rice (Rajib Das  et al., 2015).

Based on this research, it can be said that for getting higher yield and net returns application of Pyrazosulfuron followed by Florpyrauxifen-benzyl + Penoxsulam 25 DAT(T8) or Triafamone 20%+ Ethoxysulfuron 10% WG@ 225 g/ha at 20 DAT(T10) or hand weeding is recommended for transplanted rice during kharif season.

The authors declare that there is no conflict of interest related to this article.