Allelopathic influence of fly ash and nitrogen on growth, yield attributes and productivity of mustard (Brassica juncea L.)

Introduction

Mustard (Brassica juncea L.) belonging to family Cruciferae is one of the most important rabi oilseed crops of northern India, contributing nearly 30% of total oilseed production and ranking second after groundnut (FAI, 2018) [4] . India leads globally in area under mustard and holds second position in production after China. In Punjab, mustard is cultivated on approximately 0.82 lakh hectares with a productivity of 926 kg/ha, considerably below the national average of 1581 kg/ha (FAI, 2018) [4] , highlighting the need for improved agronomic practices. Edible oils from mustard are concentrated sources of essential fatty acids and fat-soluble vitamins, but current domestic oilseed production meets only about 50% of national demand (Khobragade et al., 2008) [7] . Nitrogen is the most critical macronutrient for mustard, constituting protoplasm, chlorophyll and metabolically active proteins (Reddy and Reddy, 1998) [17] . Brassica species remove large quantities of nitrogen until flowering, and yield responses to nitrogen up to 87.5 kg/ha have been well documented (Malav et al., 2024; Singh et al., 2022; Sharma et al., 2022) [11,22,20] . Fly ash (FA), the residue from coal combustion in thermal power plants, is generated in excess of 100 million tonnes annually in India (Mathur et al., 2003) [12] . Its enrichment with calcium oxide, magnesium oxide, silicon dioxide and trace micronutrients enables FA to modify soil pH, bulk density, moisture retention and nutrient availability effects ecologically analogous to those of soil-applied allelochemicals (Adriano and Weber, 2001; Kuchanwar and Matte, 1997) [1,8] . Recent studies have demonstrated significant yield improvements in Brassica crops from FA application (Singh et al., 2020; Jana et al., 2017; Sasmita Dash et al., 2017) [21,5,19] . However, the combined agronomic and biochemical effect of FA and nitrogen on mustard var. GSC-7 under Punjab's semi-arid conditions remains unquantified. The present investigation was undertaken to evaluate the effect of fly ash and nitrogen levels on growth and seed yield of mustard; and assess economic returns of different treatment combinations.

Materials and Methods

Experimental site and climate

The experiment was conducted during the rabi season (October 2024 -March 2025) at the Agricultural Research Farm, Guru Kashi University, Talwandi Sabo, Bathinda, Punjab, India (29°57′N; 75°07′E; 213 m asl). The region has a sub-tropical, semi-arid climate with maximum summer temperature of 45°C and minimum winter temperature of 0.5°C. Mean annual rainfall is approximately 650 mm, of which three-fourths arrives during the south-west monsoon (July-September). Weekly meteorological data recorded during the crop season are presented in Table 1.

Soil characteristics

Composite soil samples from 0-15 and 15-30 cm depths were analysed for physico-chemical properties prior to sowing (Table 2). The soil was loamy sand in texture, slightly alkaline (pH 7.6-8.0), low in organic carbon (0.12-0.24%) and available nitrogen (103-206 kg/ha), adequate in available phosphorus (26.2 kg/ha) and potassium (150-217 kg/ha).

Treatments and experimental design

The experiment was laid out in a Split Plot Design (SPD) with three replications. Main plots comprised three fly ash levels: F₀ = 0 t/ha, F₁ = 5 t/ha and F₂ = 10 t/ha. Sub-plots comprised four nitrogen levels: N₀ = 0 kg/ha, N₁ = 37.5 kg/ha, N₂ = 62.5 kg/ha and N₃ = 87.5 kg/ha, giving 12 treatment combinations. Net plot size was 3.0 × 3.0 m. Variety GSC-7 was used throughout.

Crop management

Field preparation comprised two disc harrow passes followed by planking after pre-sowing irrigation. Fly ash was incorporated as per treatments before the last planking. A basal dose of 30 kg P₂O₅/ha (single super phosphate) and 15 kg K₂O/ha (muriate of potash) was applied uniformly. Fifty percent of allocated nitrogen (as urea, 46% N) was applied basally; the remaining 50% was top-dressed after the first irrigation. Variety GSC-7 was sown on 03 October 2024 at 3.75 kg/ha seed rate with 30 cm row spacing. Thinning at 22 days after sowing (DAS) maintained 15 cm plant-to-plant spacing. Three irrigations were given at 35, 75 and 95 DAS. Crop protection included Thiamethoxam 25 WG (100 g/ha) against aphids and Mancozeb 75 WP (625 g/ha) against Alternaria blight.

Observations and statistical analysis

Plant height (cm), primary and secondary branches per plant were recorded at maturity. Leaf area index was measured at 90 DAS using a Sun Scan Canopy Analyser. Yield attributes siliquae per plant, siliqua length (cm), grains per siliqua and 1000-grain weight (g) were recorded at harvest. Stover yield (q/ha) and seed yield (q/ha) were recorded after threshing and cleaning. Economic analysis used prevailing market prices. Data were subjected to ANOVA for SPD and treatment means compared using the Critical Difference (CD) at P=0.05.

Results and Discussion

Plant height (cm) Plant height increased significantly with nitrogen and fly ash levels (Table 3). N₃ (87.5 kg/ha) gave the highest mean plant height (141.83 cm) and F₂ (10 t/ha) gave the tallest mean (137.47 cm). The interaction F₂N₃ recorded maximum plant height (143.44 cm) versus minimum in F₀N₀ (123.13 cm). Enhanced height with nitrogen is attributed to increased cell division, elongation and photosynthate production (Joshi et al., 1991) [6] , while FA through its alkaline chemistry and micronutrient supply created a growth-stimulatory rhizosphere environment (Sarita Gautam et al., 2013) [18] . Similar findings were reported by Ansari et al. (2022) [2] and Kumar et al. (2021) [10] . 5).

Increased branching with nitrogen reflects improved auxin and cytokinin synthesis promoting axillary bud development (Kumar and Kumar, 2008) [9] . FA-stimulated branching is consistent with Kuchanwar and Matte (1997) [8] and Sasmita Dash et al. (2017) [19] who documented similar responses in Brassica crops.

Siliquae per plant and siliqua length

Siliquae per plant differed significantly due to both factors and their interaction (Table 6). F₂ gave the highest fly ash mean (1357.83) and N₃ gave the highest nitrogen mean (1422.44). The interaction F₂N₂ recorded the maximum (1500.67) and F₀N₀ the minimum (921.67). Nitrogen promotes cytokinin synthesis stimulating siliqua set, while FA improved soil structure and photosynthate supply to reproductive sinks, aligning with Ram et al. (2013) [13] and Singh et al. (2020) [21] . Siliqua length increased with both treatments (Table 7), with F₂ recording 5.34 cm and N₃ giving the highest mean (5.61 cm). Longer siliquae with higher nitrogen indicate improved assimilate supply to developing pods (Reager et al., 2006) [16] .

Grains per siliqua and 1000-grain weight

Grains per siliqua responded significantly to all treatments (Table 8). F₂ gave the highest mean (21.50) and N₃ gave the highest nitrogen mean (22.56), with F₂N₂ recording the maximum (24.00). Test weight was significantly influenced only by nitrogen levels; the fly ash effect and interaction were nonsignificant (Table 9). N₃ gave the highest test weight (4.51 g). Improved seed set with FA corroborates Swamy et al. (2010) [23] , while the nitrogen response aligns with Malav et al. (2024) [11] and Sharma et al. (2022) [20] .

Stover yield and seed yield

Stover yield increased significantly with both treatments (Table 10). F₂ gave the highest mean (22.73 q/ha) and N₃ gave the highest nitrogen mean (25.19 q/ha), with F₂N₃ recording the maximum (25.81 q/ha) versus F₀N₀ minimum (14.93 q/ha). Seed yield showed a significant response to all factors (Table 11). F₂ gave the highest fly ash mean (10.85 q/ha) compared to F₀ (9.83 q/ha). N₃ gave the highest nitrogen mean (11.68 q/ha), statistically at par with N₂ (11.35 q/ha). The maximum seed yield (12.68 q/ha) was recorded in F₂N₃ and the minimum (7.36 q/ha) in F₀N₀. Higher seed yield with nitrogen is attributable to better branching, siliqua number and grain filling, while FAmediated improvements in soil conditions enhanced nitrogenuse efficiency (Singh et al., 2020; Jana et al., 2017; Rautaray et al., 2003) [21,5,15] .

Economic analysis

The benefit-to-cost (B:C) ratio improved with increasing levels of both inputs (Table 12). The highest cost of cultivation (₹40,600/ha) was recorded under F₂N₃, yet this treatment also gave the maximum gross return (₹89,760/ha), net return (₹49,160/ha) and B:C ratio (2.21) rising from 1.43 under F₀N₀. These results are consistent with Malav et al. (2024) [11] and Singh et al. (2022) [22] , confirming the economic advantage of combining fly ash with optimised nitrogen in Brassica cultivation.

Conclusion

Fly ash at 10 t/ha acts as a bioactive soil amendment with growth-stimulatory biochemical effects on mustard (Brassica juncea L.) analogous to allelopathic enhancement, by modifying the soil chemical environment and improving nutrient availability. Combined application of fly ash at 10 t/ha and nitrogen at 87.5 kg/ha (F₂N₃) recorded the highest seed yield (12.68 q/ha), net return (₹49,160/ha) and B:C ratio (2.21), and is recommended for mustard cultivation in the loamy-sand soils of semi-arid Punjab. Fly ash utilisation as a soil amendment provides an environmentally responsible approach to managing industrial coal combustion residue while enhancing crop productivity. Future research should examine the long-term soil health implications of repeated fly ash application and validate these findings over multiple seasons.

Acknowledgement

AcknowledgmentsThe authors thank the staff of the Agricultural Research Farm, Guru Kashi University for technical assistance during field operations and the Department of Meteorology for providing meteorological data recorded at Talwandi Sabo, Bathinda during the crop season 2024-25.

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