Effect of pre and post-emergence herbicides on growth, yield attributes and yield of blackgram [Vigna mungo (L.) Hepper] in Chhattisgarh plains

Introduction

Blackgram is one of the major pulse crops grown in India. Blackgram [Vigna mungo (L.) Hepper] is a dicotyledonous plant belonging to the family Fabaceae. Blackgram, commonly referred to as urdbean in most parts of India, is cultivated in tropical and subtropical regions for grains, green manure, fodder, and forage. It is grown as a sole crop, intercrop, mixed crop, and in sequential cropping systems. Blackgram is commonly consumed in the form of dal (whole or split, with or without husk) or as roasted grains. It is the main ingredient in the preparation of papad and bari (spiced dumplings), which are used to prepare a tasty curry. It differs from other pulses in its peculiarity of attaining, when up with water, a somewhat mucilaginous pasty character, giving additional body to the mass. In southern India, the dehusked dal is ground into a smooth batter, fermented, and blended with an equal proportion of rice flour to prepare traditional foods such as Dosa and Idli. The grains are also deep-fried to make savoury dishes. Urd dal is further utilised in the preparation of sweets like Halwa and Imarti. In addition, blackgram serves as a nutritious fodder crop, particularly for feeding livestock. It is also cultivated as a green manure crop to improve soil productivity. Nutritionally, blackgram is rich in phosphoric acid, vitamins, and minerals, with 24% protein, 60% carbohydrates, and 1.3% fat. (Islam et al., 2011) [6] . The total area under blackgram cultivation in India is about 5.89 lakh ha, and the production is 22.42 lakh tonnes with an average productivity 3.81 tonnes/ha (Anonymous, 2024) [1] . In Chhattisgarh, the total black gram area is 65.26 thousand ha area with production of 25.17 thousand tons and an average productivity of 0.38 tonne/ha (Anonymous 2024) [2] . Pulse crops generally exhibit slow growth during the early seedling stage. Moreover, during the initial period, they develop a limited canopy due to fewer branches and smaller leaf area, which lowers their ability to compete effectively with weeds. In black gram (Vigna mungo), weed infestation can cause yield losses of about 45 to 60 percent. Furthermore, with the development of short-statured, compact and early-maturing cultivars, the weed problem has become more serious. (Sasikala et al. 2014) [11] . There are various factors that contribute to the low yield of black gram. i.e losses caused by agricultural pests, such as insects, nematodes, disease, rodents, etc. Among the various constraints to realize its potential yield, weeds are the major hindrance in exploiting the full utilization of production factors for higher yield. [8] . Timely weed control is essential for higher black gram yield. Although hand weeding is effective, it is labour-intensive, costly, and often delayed due to labour shortage and rainy conditions, reducing its effectiveness compared with timely weed management. The chemical method of weed control is economical and effective in reducing weed infestation for a longer duration when applied properly. In recent years, several new herbicide molecules have been developed that provide higher weed control efficiency even at lower doses, with shorter persistence and reduced toxicity to mammals. These herbicides are broad-spectrum in action and offer a wider period of application. Their environmental advantage lies in the very low application rate in grams rather than kilograms per hectare, which significantly decreases the chemical burden on the environment. But certain important factors must be considered while applying herbicides for weed control. The herbicides should be selective to the crop and should not leave harmful residues in the soil that may affect the succeeding crops in the rotation. In pulse crops, special attention is required because these chemicals should not damage the soil microflora responsible for maintaining soil fertility or the root-nodule forming organisms that fix atmospheric nitrogen.

Materials and Methods

Climate Condition:

During the experimental period, the area experienced high to moderate temperatures, with average daily temperatures ranging between 26.5 °C and 30.1 °C, and relative humidity fluctuating between 61% and 95%. The minimum rainfall received during the crop growing period was 1.6 mm, and the maximum rainfall of 32.2 mm.

Treatment details

The experiment was laid out in a Randomized Block Design (RBD) with seven treatments replicated thrice. The treatments were T 1 -Weedy Check, T 2 -Weed free, T 3 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as preemergence , T 4 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Quizalofop ethyl (5% EC) @ 0.05 Kg a.i. ha -1 as post-emergence at 20 DAS, T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS , T 6 -Quizalofop ethyl (5% EC) @ 0.05 Kg a.i. ha - 1 as post-emergence at 20 DAS , T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS.

Statistical analysis

The data collected for all the characters were subjected to statistical analysis as per the procedure of Randomized Block Design with factorial concept in OPSTAT. The 'F' test was used for the test of significance. The Standard Error of Mean (S.Em.±) was computed in each case. For the treatment effects which were found significant, the critical difference (C.D.) at 5 percent level of probability was worked out to compare the treatment means. Weed free T3 Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence T4 Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Quizalofop ethyl (5% EC) @ 0.05 Kg a.i. ha -1 as post-emergence at 20 DAS T5 Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS T6

Quizalofop ethyl (5% EC) @ 0.05 Kg a.i. ha -1 as post-emergence at 20 DAS T7 Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS

Results and Discussion

Growth parameters 3.1.1 Plant population

The plant population did not differ significantly among treatments, indicating a uniform plant stand under various weed management treatments. These results are also in accordance with the findings of Dhayal et al. (2022) [4] .

Plant height

Plant height at 30, 60 DAS and at harvest revealed significant differences among the treatments. At all observation stages, significantly taller plants were recorded under weed free (T₂), followed by T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS and T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS, while the control plot (T₁) recorded the shortest plants. The increase in plant height is due to eliminating weed competition throughout the crop growth period, enabling better resource utilization, eliminating weed competition throughout the crop growth period, reduce competition and promoting photosynthesis. These results are also in accordance with the findings of Dhayal et al. (2022) [4] .

Number of branches plant -1

At 30,60 DAS and at harvest, a significantly maximum number of branches were found under weed free (T₂), followed by T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha - 1 as post-emergence at 20 DAS and T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS, while the Weedy Check plot (T₁) recorded the lower number of branches. The increase in number of branches is due to reduced weed competition and better utilisation of growth resources. Similar findings were also reported by Reddy et al. (2022) [10] .

Number of leaves plant -1

A clear difference in leaf number was recorded among treatments during the crop growth period. At 30,60 DAS and at harvest, significantly higher leaf counts were found under weed free (T₂), followed by T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS and T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS, while the Weedy Check plot (T₁) consistently recorded the lower leaf count. The better leaf initiation is due to reduced crop-weed competition for nutrients, light, moisture, space and higher photosynthetic activity. These findings are in close conformity with those of Gendlal et al.

Dry matter accumulation per plant at 30, 60 DAS and at harvest was highest under weed free (T₂). Among the chemical weed management treatments, the highest dry matter accumulation per plant was recorded under T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as preemergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS followed by T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS. The Weedy Check plot (T₁) recorded the lowest dry matter accumulation. The increase in dry matter accumulation may be attributed to effective weed control and efficient utilization of soil moisture, nutrients and solar energy. These results are in accordance with the findings of Kumar et al.

Yield attributes

Yield attributes such as number of pods per plant, seeds per pod, pod length and seed index were maximum under weed free (T₂), followed by T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS and T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS. The minimum values were recorded in the Weedy Check (T₁). This result may be due to reduced cropweed competition during the critical growth stages and more effective weed suppression under combined herbicide application, which enabled the crop to utilize adequate growth resources. This, in turn, promoted greater translocation of photosynthates towards the reproductive organs and resulted in a higher number of pods plant⁻¹. Similar findings were also reported by Reddy et al. (2022) [10] .

Grain yields were highest under weed free (T₂), followed by T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as preemergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS and T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS. The Weedy Check plot (T₁) recorded the lowest yields. The increase in Seed yield depends on efficient photosynthesis, assimilate translocation, and yield-contributing traits. Weedfree conditions and effective herbicide treatments increased seed yield by reducing weed competition and improving resource utilization. Similar findings were also reported by Nirala et al. (2012) [9] and Adhikary (2018) [3] .

stover yields were highest under weed free (T₂), followed by T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as preemergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS and T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS. The Weedy Check plot (T₁) recorded the lowest yields. The higher stover yield under weed-free conditions and effective herbicide treatments was due to reduced weed competition, better resource utilization, and increased dry matter accumulation. Similar findings were also reported by Nirala et al. (2012) [9] and Adhikary (2018) [3] .

Harvest index

The harvest index did not differ significantly among treatments. This is due to both grain yield and total biological yield increasing proportionally under different weed management practices, resulting in a similar partitioning of assimilates between grain and vegetative parts. The results are supported by the findings of Nirala et al. (2012) [9] and Adhikary (2018) [3] .

At 30, 60 DAS, and at harvest, total weed density was recorded at a minimum under weed-free (T₂). Among herbicidal treatments, at 30 DAS the significantly lowest total weed density was recorded under T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS followed by T 4 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre emergence + Quizalofop ethyl (5% EC) @ 0.05 Kg a.i. ha -1 as post-emergence at 20 DAS. At 60 DAS and at harvest, the lower weed density was recorded under T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as preemergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS, followed by T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS. The Weedy Check plot (T₁) recorded the highest weed density.

At 30, 60 DAS, and at harvest, dry matter accumulation of weed was recorded lowest under weed free (T₂), followed by T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as preemergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS and T 7-Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS. The highest values were recorded in T₁-Weedy Check (T 1 ).

At 30,60 DAS, and at harvest, Weed control efficiency (WCE) was recorded highest under T₂-Weed free (100%), followed by T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha - 1 as post-emergence at 20 DAS and T 7 -Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS. The lowest values of WCE were recorded in T₁-Weedy Check. 82 Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence 2.72 5.32 5.59 Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Quizalofop ethyl (5% EC) @ 0.05 Kg a.i. ha -1 as post-emergence at 20 DAS 3.00 5.56 5.83 Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as postemergence at 20 DAS 3.80 6.45 6.8

Quizalofop ethyl (5% EC) @ 0.05 Kg a.i. ha -1 as post-emergence at 20 DAS 2.64 5.01 5.24 Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS

Conclusion

At 30, 60 and at harvest, weed free (T 2 ) have registered higher growth, yield attributes and yield, and reduced weed dynamics. Among chemical treatment, T 5 -Pendimethalin (38.7% EC) @ 1 Kg a.i. ha -1 as pre-emergence + Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS followed by T 7-Imazethapyr (10% SL) @ 0.2 Kg a.i. ha -1 as post-emergence at 20 DAS recorded higher growth, yield attributes and yield, and reduced weed dynamics. Higher weed control efficiency was also recorded under these treatments.

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