Weed management in rainfed maize (Zea mays L.) through early post emergent herbicides

Introduction

In 2050, the world will undergo significant changes. The number of people on the planet will rise to over 9 billion, and the average global temperature will increase. Food, fuel, and other basic resources will run out. (Shenggen Fan and Brzeska, 2010, Anon., 2022) [14,1] . Furthermore, India is a densely populated country, and its population continues to grow at a rapid rate. If the current population growth trend persists, the country may require approximately 301 million tonnes of food grains by 2050 AD, as estimated by the National Academy of Agricultural Sciences. (Shankaran et al., 2005) [11] . In India, maize is cultivated over an area of approximately 8.78 million hectares (M ha), with a total production of 21.76 million tonnes (M t). The average productivity of maize in India is about 2,478 kg ha⁻¹, which is considerably lower than the world average productivity of 4,860 kg ha⁻¹ (Anon., 2022) [1] . Maize plays a significant role in the Indian economy as it is an important source of food and animal feed and also serves as a valuable raw material for various industries. In recent years, corn oil has gained popularity among consumers because of its cholesterolfree nature. In addition, maize-derived products such as cornstarch, corn flakes, gluten, germ cake, lactic acid, alcohol, and acetone are either consumed directly as food products or utilized as raw materials in various industries, including the paper, textile, and fermentation industries. Approximately two-thirds of the total global maize production is utilized as livestock feed or for the commercial production of starch and oil (Khalil and Jan, 2004) [6] . Maize production and productivity are adversely affected by weed competition, particularly during the vegetative and early reproductive stages of crop growth. Weeds compete with maize plants for essential growth resources, including nutrients, moisture, sunlight, and space, thereby reducing crop growth and yield. Therefore, effective and timely weed management is essential for achieving higher maize productivity. The use of early postemergence herbicides may provide a viable and effective alternative to conventional weed management practices. Early post-emergence application of herbicides may involve the use of either a single herbicide or a combination of two herbicides. A well-planned early post-emergence application using a tank mixture of compatible herbicides can provide more effective and broad-spectrum weed control than the application of a single post-emergence herbicide.

Such herbicide combinations can effectively control both broad-leaved weeds and grassy weeds, thereby reducing weed competition during the critical growth stages of the crop. However, adequate information regarding the efficacy, compatibility, suitable combinations, application rates, and optimal timing of such herbicide mixtures is currently limited. Therefore, there is a need to evaluate suitable early post-emergence herbicide combinations for achieving effective and broad-spectrum weed management.

Materials and Methods

The trial conducted for M.Sc. student at the Department of Agronomy, S. V. U. Sagar Madhya Pradesh during kharif (rainy season) 2022 to study the "Weed management in rainfed maize (Zea mays L.) through early post emergent herbicides". The experiment was conducted in the spacing 60 x 20 cm, sowing season Kharif, 2022, fertilizer: 100:50:25 N:PO:K₂O kg ha -1 , plot size(gross) 4. Observation taken to be selected randomly five plants from sampling area than taken following observations on different growth stages up to harvest.

Plant height was measured from base of the plant to the leaf length was measured from the stage of complete leaf opening until cob emergence, and again from tasselling to the base of the collar of the flag leaf. The measurements were recorded in s cm

Leaf area per plant (dm²)

The leaf area per plant is calculated using the length × breadth method with a correction (multiplication) factor of 0.75 by (Sticker et al., 1961).

Leaf area index (LAI)

Represents the cumulative persistence of leaf area over a specific growth period. It is calculated by integrating the Leaf Area Index (LAI) over time, as originally described by Watson (1952) [20] .

Leaf area per plant (dm²) LAI = Land area occupied by the plant (dm²)

Leaf area duration days (LAD) are calculated as per formula given by (Watson, 1952) [20] and Power et al. (1967) [10] .

Where, LAD = Leaf area duration in days L. L 2 = LAI at stages 1 and 2 t 2 -t 1 = Time interval in days between stages 1 and 2.

SPAD meter reading (Chlorophyll content)

This observation taken from leaf chlorophyll content given by the processor (Clements, 1964) [2] .

This plant cut into the ground surface, dried at 70 0 c and cut inti small pieces, Total dry matter produced are calculated in different levels 30, 60, 90 and at harvest.

Yield components and yield

Yield attribute characters observed are as below.

Seeds from five randomly selected, sun-dried cobs were manually separated and weighed. The average seed weight per cob was calculated and recorded as the grain weight per cob (g).

A random sample of 100 seeds was collected from the net plot yield of each treatment. The seeds were weighed using a precision balance, and the weight was recorded in grams (g).

At physiological maturity, cobs were harvested from each treatment separately and dehusked. The harvested cobs were air-dried before shelling, and the grains obtained were thoroughly cleaned and weighed. The grain yield for each treatment was calculated and expressed in quintals per hectare (q ha⁻¹).

Statistical analysis of data

In this experiment the collected data analyzed by statistically described by Gomez and Gomez (1984). The level of significance used in 'F' test was P = 0.05 Critical difference values were calculated wherever the 'F' test was significant.

Results and Discussion

Plant height

The statistically analyzed results are presented in Table 1. Plant height in maize was significantly affected by the weed management treatments at different stages of crop growth. However, at 30 days after sowing (DAS), the treatments did not cause any significant variation in plant height. At 60 DAS, the weed-free treatment recorded the maximum plant height (175.53 cm). However, it remained statistically at par with treatments T 4 (174.55 cm), T 6 (174.49 cm), T 5 (168.00 cm), T 1 (166.87 cm), T 3 (164.72 cm), and T 2 (164.60 cm). In contrast, treatment T 8 produced the minimum plant height (150.07 cm), which was significantly lower than the other treatments. At 90 DAS, plant height was significantly influenced by the weed management treatments. The recommended practice (T₆) recorded a plant height of 193.05 cm, followed by T₄ (192.00 cm), T₅ (189.26 cm), and T₂ (175.53 cm). These treatments were statistically at par with T₇, which produced the maximum plant height of 197.97 cm. At harvest, the T 7 (check) treatment produced the tallest maize plants, recording a plant height of 204.63 cm, which was significantly higher than most other treatments. However, it remained statistically at par with T 4 (199.40 cm), T 6 (196.75 cm), and T 5 (191.60 cm). These results are in conformity with the findings of Srividya et al. (2011) [17] . Significantly lower plant height was observed in T 8 check (169.30 cm). Shinde et al. (2001) [15] , Likewise, Shekhawat and Gautham (2002) [13] recorded the higher values for all the growth parameters in weed free control, followed by hand weeding twice.

Leaf area

Leaf area of maize, measured in dm² at different growth stages up to harvest, showed significant variation among the weed management treatments (Table 2). However, at 30 DAS, the treatments did not have a significant effect on leaf area At 60 DAS, the weed management treatments had a significant effect on the leaf area of maize. [12] , Ishrat et al. (2012) [5] and Nadiger et al.

(2011) [9] . The TDMP of maize is dependent on growth attributes such as leaf area (LA).

Leaf area duration computed at (Table 3) Leaf Area Duration (LAD) exhibited a pattern similar to leaf area and Leaf Area Index (LAI) throughout all growth stages of maize. The accumulation of total dry matter production (TDMP) was closely associated with growth parameters such as plant height and LAD. In addition, LAI is an important growth indicator that reflects the plant's capacity for photosynthesis, transpiration, and biomass accumulation It is a major factor determining the solar radiation interception, canopy photosynthesis and therefore yield of maize (Duncon, 1975) [3] . [7] . Total dry matter production of maize (g plant -1 ) Total dry matter production (TDMP) of maize differed significantly due to weed management treatments (Table 5). At 30 DAS, dry matter accumulation in maize varied significantly among the weed management treatments. The highest dry matter accumulation was recorded in treatment T 7 (12.30 g plant⁻¹), which was statistically at par with T 4 and T 6 , both registering 10.26 g plant⁻¹. Treatments T 2 (8.89 g plant⁻¹) and T 5 (8.87 g plant⁻¹) also showed significantly higher dry matter accumulation and remained comparable with the recommended practice. The lowest dry matter accumulation was observed in T 8 (7.58 g plant⁻¹).

At 60 DAS, the highest dry matter accumulation was observed in T 7 (97.94 g plant⁻¹), which was statistically comparable with T 6 (94.43 g plant⁻¹), T 4 (91.50 g plant⁻¹), T 5 (86.31 g plant⁻¹), T 1 (84.34 g plant⁻¹), and T 2 (84.26 g plant⁻¹). However, T 8 produced the lowest dry matter accumulation (71.48 g plant⁻¹), which was significantly inferior to the other treatments At 90 DAS, dry matter accumulation in maize was significantly influenced by the different weed management treatments. The recommended weed management practices, T 6 (254.90 g plant⁻¹) and T 4 (250.15 g plant⁻¹), produced significantly higher dry matter accumulation and were statistically at par with T 7 (277.05 g plant⁻¹). These treatments were followed by T 5 (236.86 g plant⁻¹). The treatments involving the individual application of herbicides (T 1 , T 2 , and T 3 ) showed dry matter production comparable to that of the herbicide mixture treatments. The lowest dry matter accumulation was observed under T 8 (188.61 g plant⁻¹), which differed significantly from the other treatments At harvest, dry matter accumulation in maize varied significantly among the weed management treatments. The early post-emergence herbicide treatment T 4 recorded a dry matter production of 296.93 g plant⁻¹, while the recommended weed management practice T 6 produced 294.77 g plant⁻¹. Both treatments were statistically at par with the weed-free treatment T 7 , which registered the highest dry matter accumulation (323.64 g plant⁻¹).

Treatment T 5 also showed significantly greater dry matter production (267.01 g plant⁻¹) compared to the other herbicide treatments. In contrast, the weedy check (T 8 ) recorded the lowest dry matter accumulation (190.26 g plant⁻¹). Replaced weed density in the formula given by Mani et al. (1973) [8] by weed dry weight to calculate total dry matter production.

Yield and Yield Components of Maize

The observations on grain weight per plant, hundred grain weight, gram yield are presented in Table 6.

Grain Weight (g plant -1 ) Grain weight per plant was significantly influenced by the different weed management treatments (Table 6). Among the treatments, T 7 recorded the highest grain weight per plant (164.14 g plant⁻¹), which was significantly superior to most other treatments. However, its performance was statistically comparable with T 6 (recommended weed management practice, 145.16 g plant⁻¹) and T 4 (144.43 g plant⁻¹), as these treatments remained at par with each other. The lowest grain weight per plant was recorded under T 8 (80.06 g plant⁻¹), which was significantly inferior to all other treatments. this result is in conformity with the findings of Walia et al. (2007) [19] . [19] .

Grain yield of maize was significantly affected by the weed management treatments employed (Table 6). Among the treatments, T 7 produced the highest grain yield (7103 kg ha⁻¹), which was statistically comparable with T 6 (6882 kg ha⁻¹), T 4 (6791 kg ha⁻¹), and T 5 (6609 kg ha⁻¹). These treatments resulted in significantly greater grain yield than T 1 (topramezone alone), T 2 (atrazine alone), and T 3 (2,4-D alone). The lowest grain yield was observed under T 8 (4973 kg ha⁻¹), which was significantly inferior to all other weed management treatments. These results are in conformity with the findings of Srividya et al. (2011) [17] .

Conclusion

At both 30 and 60 DAS, the tank mixture treatments (T 4 and T 5 ) significantly reduced the population of broad-leaved weeds, grassy weeds, sedges, and the overall weed dry matter accumulation. Their performance was statistically comparable to the recommended weed management practice. In contrast, the weedy check treatment exhibited the highest weed density and dry weight. The herbicide tank mixture treatment T 4 resulted in effective weed suppression and recorded a low weed index (4.38%), which was statistically comparable to the recommended weed management practice. Similarly, the pre-emergence herbicide treatments T 6 (3.19%) and T 5 (7.05%) also maintained a low weed index, indicating effective weed control At both observation stages (30 and 60 DAS), the tank mixture treatment T 4 exhibited the highest weed control index (WCI), recording 75.99% at 30 DAS and 86.11% at 60 DAS. These values were statistically comparable with T 5 (70.11% and 79.24% at 30 and 60 DAS, respectively) as well as the recommended weed management practice T 6 (77.69% and 88.36% at 30 and 60 DAS, respectively).

At all crop growth stages, the application of tank mixture T 4 resulted in the greatest plant height and was significantly superior to the other weed management treatments. Treatment T 5 produced the second-highest plant height and remained statistically at par with T 4 . In contrast, T 8 consistently recorded the lowest plant height throughout all stages of crop growth. Grain weight per plant was significantly influenced by different weed management treatments. The recommended weed management practice (T 6 ) produced the highest grain weight per plant (145.16 g plant⁻¹), followed closely by treatment T 4 (144.43 g plant⁻¹). Both treatments were statistically at par with the weed-free treatment. In contrast, the lowest grain weight per plant (80.06 g plant⁻¹) was recorded under treatment T 8 .

Grain yield was significantly influenced by the weed management treatments. The tank mixtures T 4 (6791 kg ha⁻¹) and T 5 (6609 kg ha⁻¹) produced significantly higher grain yields than their respective single-herbicide applications. However, the yields obtained with T 4 and T 5 were statistically comparable with the recommended weed management practice T 6 (6882 kg ha⁻¹) and T 7 (7103 kg ha⁻¹). In contrast, T 8 recorded the lowest grain yield of 4973 kg ha⁻¹.

Acknowledgement

AcknowledgmentsI sincerely express my gratitude to the Head, Department of Agronomy, SVU, Sagar (M.P.), for providing the necessary facilities and support to conduct the experiment during Kharif 2022 at the experimental field. I am also thankful to all the staff members of the Agricultural Research Station under Dr. PDKV, Akola, for their valuable assistance and cooperation. I extend my heartfelt thanks to my friends for their help in recording observations, data analysis, and laboratory work, which contributed greatly to the successful completion of this experiment.

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