Effect of nitrogen levels and row spacing on growth and yield of Indian Mustard (Brassica juncea L.)

Introduction

Indian mustard (Brassica juncea L.), belonging to the family Brassicaceae, is one of the oldest and most economically important oilseed crops in the world. The Brassicaceae family comprises approximately 3,500 species and 350 genera, ranking among the ten most economically significant plant families globally (Chauhan et al., 2020) [5] . Rapeseed and mustard collectively constitute the third most important edible oilseed crop worldwide, after soybean and palm oil and play a major role in meeting the dietary requirements of South Asia (ICAR-DRMR, 2022) [14] . The two most widely cultivated species are Brassica juncea and Brassica campestris, with seed oil content ranging from 37 to 49%. Globally, the total area, production and yield of rapeseed-mustard in 2023-24 were 42.53 million hectares, 88.07 million metric tonnes and 2.07 metric tonnes per hectare, respectively. India accounts for 19.8% of the total global acreage and 9.8% of total production (ICAR-DRMR, 2024) [14] . In India, mustard is grown over approximately 6.26 million hectares with a production of 8.68 million tonnes and productivity of 1.3 t/ha. In Uttar Pradesh, rapeseed-mustard covers 1.27 million hectares with a production of 1.9 million tonnes and productivity of 1.5 t/ha (GOI, 2023). Nitrogen is the most critical macronutrient influencing the vegetative growth, leaf area expansion and seed yield in mustard. Brassica species, despite having high nitrogen absorption efficiency, exhibit low translocation efficiency towards reproductive organs, resulting in reduced nitrogen utilization efficiency (Kumar et al., 2018) [21] . Indian mustard is highly sensitive to nitrogen deficiency, which causes chlorosis and dwarfing, ultimately reducing productivity (Rana et al., 2021) [31] . Approximately 90% of Indian soils, particularly in the Gangetic plains, exhibit low to medium levels of nitrogen, phosphorus and potassium (Sharma and Meena, 2019) [32] , making nitrogen management a major challenge in rapeseed-mustard production.

Row spacing is a non-monetary but critical agronomic input that regulates plant population density, inter-plant competition and resource use efficiency. Optimum row spacing ensures better light interception at each leaf stratum, enhancing photosynthesis, dry matter production and crop yield (Alam and Singh, 2018) [1] . Establishment of optimum plant population through proper row spacing is essential for better translocation of photosynthates and higher crop yield (Sondhiya et al., 2019; Singh et al., 2024) [35, 34] . The present investigation was therefore undertaken to study the effect of nitrogen levels and row spacing on growth and yield of Indian mustard, with particular focus on assessing crop productivity under the baseline soil constraints of the region.

Materials and Methods

Experimental Site and Period

The field experiment was conducted during the Rabi season of 2025-2026 at the Crop Research Farm, Department of Agronomy, SHUATS, Prayagraj (U.P.), India. The experimental site is located at 25.28°N latitude, 81.54°E longitude and 98 m altitude above mean sea level, situated on the right bank of the river Yamuna, approximately 5 km from Prayagraj city.

Climate

Prayagraj experiences a sub-tropical and semi-arid climate with extreme temperatures in both winter and summer. The southwest monsoon commences in July and withdraws by the end of September. During the cropping season (Rabi 2025-2026), meteorological data including weekly average maximum and minimum temperatures, relative humidity and rainfall were recorded at the Agrometeorological Observatory Unit, School of Forestry and Environmental Sciences, SHUATS, Prayagraj.

Soil Characteristics

The experimental field soil was sandy loam in texture, neutral in pH, non-saline in electrical conductivity and low in organic carbon. Composite soil samples were collected from a depth of 0-15 cm prior to sowing for physical and chemical analysis. The pre-sowing chemical and physical characteristics of the soil, along with the standardized methodologies used for analysis, are detailed in Table 1. [30]

Experimental Design and Treatments

The experiment was laid out in a Randomized Block Design (RBD) with 12 treatment combinations replicated thrice. The treatments comprised four levels of nitrogen (N₁ = 80, N₂ = 100, N₃ = 120, N₄ = 140 kg N/ha) and three row spacings (S₁ = 20 cm, S₂ = 25 cm, S₃ = 30 cm), as detailed in Table 2.

Crop Management

The mustard variety Azad Mahak was selected for the experiment. The field was prepared by ploughing twice with a tractor-drawn cultivator to achieve a fine and friable soil structure. Seeds were sown manually in lines on 12 November 2025 at a depth of 3-4 cm, with plant-to-plant spacing of 10 cm. Seeds were treated with Mancozeb (75% WP) at 3 g/kg seed, 24 hours before sowing.

Half the recommended nitrogen dose along with the full recommended doses of phosphorus and potassium were applied at sowing. The remaining half of nitrogen was applied at 20 DAS as top dressing. Gap filling and thinning were carried out at 8 DAS to maintain the desired plant population. Two hand weedings were performed at 20 and 40 DAS. Five irrigations were provided during the crop period. The crop was harvested at 125 DAS when leaves turned yellow and siliquae attained proper colour.

Observations Recorded

Pre-harvest observations were recorded at 20, 40, 60 and 80 DAS: (i) Plant height (cm) -measured from ground level to the tip of the main shoot on five randomly tagged plants per plot;

(ii) Plant dry weight (g/plant) -five representative plants were uprooted, sun-dried and oven-dried at 65-70°C to constant weight; (iii) Crop Growth Rate (CGR, g/m 2 /day) = (W₂ -W₁) / S(t₂ -t₁) where W₁ and W₂ are dry weights per unit area at times t₁ and t₂ and S is spacing; (iv) Relative Growth Rate (RGR, g/g/day) = (logₑ W₂ -logₑ W₁) / (t₂ -t₁) (Keerthi et al., 2017) [19] .

Post-harvest observations included: number of siliquae/m 2 , number of seeds/siliqua, test weight (g per 1000 seeds), seed yield (t/ha), straw yield (t/ha) and harvest index (%) = (Seed yield / Biological yield) × 100.

Statistical Analysis

Data were subjected to analysis of variance (ANOVA) using the F-test procedure of Sheoran et al. (2018) [33] . Significant differences between treatment means were tested using the Critical Difference (CD) at the 5% probability level.

Results and Discussion

Plant height increased progressively from 20 DAS to 80 DAS across all treatments (Table 3). At 20 DAS, no significant differences were observed. Significant differences emerged at 40, 60 and 80 DAS. At 80 DAS, the highest plant height (82.80 cm) was recorded in T 2 (80 kg N/ha + 25 cm row spacing), which was statistically at par with T 3 (82.51 cm) and T 4 (74.45 cm). The lowest plant height (65.59 cm) was recorded in T 12 (140 kg N/ha + 30 cm).

The superior plant height under T 2 may be attributed to the optimum nitrogen supply at 80 kg N/ha, which promoted cell elongation and vegetative growth without causing luxuriant vegetative growth or lodging. The 25 cm row spacing provided adequate inter-plant space for light interception and reduced competition, facilitating better nutrient and moisture uptake. These results are in conformity with the findings of Bano et al.

(2021) [3] , Kumar et al. (2018) [21] and Singh et al. (2024) [34] , who reported that moderate nitrogen levels combined with optimum spacing significantly enhanced plant height in mustard by reducing competition for light.

Dry weight increased steadily from 20 DAS to 80 DAS across all treatments (Table 4). At 80 DAS, the highest dry weight (18.66 g/plant) was recorded in T 2 (80 kg N/ha + 25 cm), which was statistically at par with T 1 (18.01 g/plant) and T 3 (16.20 g/plant). The lowest dry weight (10.79 g/plant) was recorded in T 11 (140 kg N/ha + 25 cm). The higher dry matter accumulation under T 2 can be attributed to better photosynthetic efficiency, improved nutrient uptake and reduced inter-plant competition at 25 cm spacing. Wider spacing and optimum nitrogen supply enhanced root proliferation and nutrient uptake activity, leading to greater water and nutrient uptake and higher dry matter accumulation, as also reported by Chaudhary et al. (2018) [4] and Singh et al. (2024) [34] . Excessive nitrogen (140 kg N/ha) may have caused luxury consumption and imbalanced vegetative growth, reducing assimilate partitioning efficiency. [19] and Lalruatfeli et al. (2021) [24] . Similar trends were observed by Tripathi et al. (2015) [36] and Yadav et al. (2016) [37] .

Yield and Yield Attributes

Data on yield and yield attributes are presented in Table 7. The treatment T 2 (80 kg N/ha + 25 cm row spacing) consistently achieved superior performance across all yield parameters.

Number of Siliquae/m 2

Significant differences were observed among treatments for the number of siliquae/m 2 . The highest number of siliquae/m 2 (10,147.3) was recorded in T 2 (80 kg N/ha + 25 cm), which was statistically at par with T 4 (10,156.0) and T 7 (10,131.3). The lowest was recorded in T 12 (6,740.7). The higher siliqua number under T 2 is attributed to better branching, improved photosynthate supply and reduced inter-plant competition at 25 cm spacing. Lower plant population at wider spacing generally increases siliquae per plant, while optimum nitrogen supply supports reproductive development. These findings are in agreement with Gupta et al. (2022) [12] , Kumar et al. (2018) [21] and Patel et al. (2024) [28] .

The highest test weight (4.98 g) was recorded in T 2 (80 kg N/ha + 25 cm), while the lowest (3.50 g) was in T 10 (140 kg N/ha + 20 cm). Test weight in mustard increased significantly with optimum nitrogen levels and spacing due to improved photosynthesis, nutrient uptake and efficient seed filling, resulting in bolder seeds. Similar findings were reported by Chaudhary et al. (2018) [4] and Anuroop et al. (2024) [2] .

Seeds per Siliqua

The highest number of seeds/siliqua (8.27) was recorded in T 2 (80 kg N/ha + 25 cm), while the lowest (7.40) was in T 10 . The lower seeds/siliqua under closer spacing is attributed to greater plant competition for environmental resources, reducing photosynthetic material production and its transfer to seeds, as reported by Anuroop et al. (2024) [2] , Dhruv et al. (2021) [10] and Lalruatfeli et al. (2021) [24] .

The highest straw yield (9.60 t/ha) was recorded in T 2 (80 kg N/ha + 25 cm), while the lowest (5.84 t/ha) was in T 12 (140 kg N/ha + 30 cm). The superior straw yield under T 2 reflects better vegetative biomass accumulation due to optimum nitrogen supply and spacing. These results are in alignment with Dekhane et al. (2024) [7] , Jha et al. (2022) [18] and Lakra et al. (2018) [23] .

The highest seed yield (3.89 t/ha) was recorded in T 2 (80 kg N/ha + 25 cm), which was statistically at par with T 1 (3.87 t/ha) and T 3 (3.25 t/ha). The lowest seed yield was recorded in T 5 (2.08 t/ha). The superior seed yield under T 2 is attributed to the combined effect of optimum nitrogen supply promoting vegetative growth and reproductive development and 25 cm row spacing ensuring adequate light interception, reduced competition and efficient resource utilization. These results are consistent with Kumar et al. (2018) [21] , Meena et al. (2024) [26] and Nayak et al. (2022) [27] .

The highest harvest index (30.2%) was recorded in T 2 (80 kg N/ha + 25 cm), while the lowest (14.6%) was in T 10 (140 kg N/ha + 20 cm). A higher harvest index indicates more efficient partitioning of assimilates towards economic yield (seeds). The superior harvest index under T 2 reflects a balanced vegetativeto-reproductive growth ratio, facilitated by optimum nitrogen and spacing. 2), which represents the optimal range for the availability of essential macronutrients and micronutrients in alluvial soils of the Indo-Gangetic plains.

Neutral pH values prevent nutrient lockup, particularly phosphorus and nitrogen, thereby ensuring that applied fertilizers are efficiently absorbed by the root system of Brassica juncea. This is supported by Sharma and Meena (2019) [32] , who noted that maintaining neutral soil pH is highly conducive to maximizing fertilizer use efficiency in oilseed brassicas.

The baseline electrical conductivity (EC) of 0.29 dS/m indicates that the soil is completely non-saline. Salinity induces osmotic stress, which impedes water uptake and seed germination in mustard. An EC value below 2.0 dS/m ensures that root osmotic potential remains unhindered, facilitating regular water uptake and plant transpiration necessary for vegetative dry weight accumulation. Gupta et al. (2022) [12] highlighted that low salinity soil allows ideal root elongation and cell division, corresponding directly to enhanced crop dry weight and plant height.

Crucially, the soil was found to be highly deficient in organic carbon, recording a low value of 0.36%. Organic carbon is the primary indicator of soil organic matter and soil health, serving as a reservoir for indigenous nitrogen supply. The low baseline organic carbon explains the highly significant positive response of Indian mustard to external nitrogen levels observed in this study. In organic carbon-deficient soils, the crop is highly dependent on mineral nitrogen fertilization. Moderate application at 80 kg N/ha (treatment T 2 ) provided the requisite nitrogen flux to satisfy the vegetative demand of Azad Mahak variety, overcoming the low native soil nitrogen supplying capacity without inducing lodging. As reported by Kumar et al.

(2018) [21] , crop response to chemical nitrogen is highly pronounced in soils with low organic carbon, where optimum agronomic management and plant geometry are essential to maximize nutrient recovery.

Summary

The present investigation on the effect of nitrogen levels and row spacing on growth and yield of Indian mustard (Brassica juncea L.) was conducted at the Crop Research Farm, Department of Agronomy, SHUATS, Prayagraj during Rabi 2025-2026 using a Randomized Block Design with 12 treatment combinations replicated thrice. The experimental field consisted of sandy loam soil with neutral pH (7.10), low electrical conductivity (0.29 dS/m) and low organic carbon content (0.36%), which supported a positive response to nitrogen application. Among the treatments, the application of 80 kg N/ha with 25 cm row spacing (T geometry. Hence, it can be concluded that the application of 80 kg N/ha with 25 cm row spacing is the most suitable treatment combination for maximizing growth and yield of Indian mustard under the agro-climatic conditions of Prayagraj, Uttar Pradesh.

Conclusion

Application of 80 Kg N/ha + Row Spacing 25 cm (Treatment 2) was recorded higher yield (3.89 t/ha), and benefit cost ratio (2.80).

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