Effect of various sources and levels of sulphur on growth, yield and quality of Indian Mustard (Brassica juncea L.)

Introduction

Indian mustard (Brassica juncea L.) is a major Rabi oilseed crop of India and has a central role in edible oil security, rural livelihoods and crop diversification. The crop is widely cultivated in northern and central India because of its adaptability to cool and dry winter conditions, short duration and comparatively better performance under medium-input farming systems. Mustard seed is valued for edible oil, spice, green leaves and oil cake, while its nutritional importance is linked with oil, protein, fibre and biologically active compounds (Bhowmik et al., 2014; Bareliya et al., 2023) [2,1] . Balanced fertilization is one of the major requirements for improving mustard productivity. Among secondary nutrients, sulphur has a specific significance in Brassica crops because it is a constituent of cysteine, cystine and methionine, and is involved in chlorophyll formation, enzyme activation, oil biosynthesis and glucosinolate metabolism. A shortage of sulphur reduces vegetative growth, delays reproductive development, decreases nutrient use efficiency and ultimately lowers seed yield and oil quality (Falk et al., 2007; Havlin et al., 2013; Singh et al., 2015) [7,9,24] . Sulphur deficiency has become more common in intensive cropping systems due to reduced use of organic manures, limited recycling of crop residues and increasing application of highanalysis sulphur-free fertilizers. Oilseed crops remove a larger quantity of sulphur than cereals, and their response to sulphur fertilization is therefore more pronounced (Khalid et al., 2011; Tiwari and Gupta, 2006) [13,26] . For mustard growers, the choice of sulphur source is as important as the dose because gypsum, SSP and bentonite sulphur differ in solubility, nutrient composition and release pattern.

Gypsum supplies sulphur in readily available sulphate form, SSP provides sulphur along with phosphorus, whereas bentonite sulphur releases sulphate gradually after microbial oxidation and may maintain availability for a longer period during crop growth. Earlier studies have reported significant improvement in growth, yield attributes, seed yield, oil content and economics of mustard with suitable sulphur sources and doses (Chattopadhyay and Ghosh, 2012; Kumar and Trivedi, 2012; Jena et al., 2021; Tiwari et al., 2021) [3,16,12,27] . However, local validation is necessary because response varies with soil texture, native sulphur status, moisture regime and climate. Considering the low available sulphur status of the experimental soil and the need to identify an efficient sulphur source for mustard cultivation in the Gwalior region, the present study was undertaken to assess the effect of various sulphur sources and levels on growth, yield, quality, nutrient uptake and economics of Indian mustard.

Materials and Methods

Experimental site and soil

The field experiment was conducted during the rabi season of 2025-26 at the Agriculture Research and Development Centre, Sakatpura, Vikrant University, Gwalior, Madhya Pradesh. The experimental site falls under a semi-arid to subtropical climatic zone with hot summers, moderate monsoon rainfall and cool dry winters. During the crop season, temperature and moisture conditions were suitable for normal germination, vegetative growth, flowering and seed development of Indian mustard. Before sowing, composite soil samples were collected from 0-15 cm depth and analyzed using standard procedures. The soil was sandy loam in texture, nearly neutral in reaction, non-saline and low in available nitrogen, medium in available phosphorus and adequate in available potassium. The initial soil properties are presented in Table 1.

Experimental design, treatments and crop management

The experiment was arranged in randomized block design (RBD) with ten treatments and three replications. The gross plot size was 4.8 m × 3.6 m and the net plot size was 3.9 m × 2.7 m. Indian mustard variety Bombay-76 was sown manually with a seed rate of 5 kg ha⁻¹ at 35 cm × 10 cm spacing. The recommended fertilizer dose was 80:40:40 kg N: P₂O₅: K₂O ha⁻¹. Half nitrogen and the full dose of phosphorus, potassium and sulphur were applied at sowing as basal dose, while the remaining nitrogen was top-dressed at first irrigation.

Treatment

Treatment details T1 Absolute control T2 100% RDF + Gypsum @ 40 kg S ha⁻¹ T3 100% RDF + Gypsum @ 50 kg S ha⁻¹ T4 100% RDF + Gypsum @ 60 kg S ha⁻¹ T5 100% RDF + SSP @ 40 kg S ha⁻¹ T6 100% RDF + SSP @ 50 kg S ha⁻¹ T7 100% RDF + SSP @ 60 kg S ha⁻¹ T8 100% RDF + Bentonite @ 40 kg S ha⁻¹ T9 100% RDF + Bentonite @ 50 kg S ha⁻¹ T10 100% RDF + Bentonite @ 60 kg S ha⁻¹

The crop was raised with uniform agronomic practices in all plots. Thinning and gap filling were done after establishment to maintain optimum plant population. Irrigations were applied at branching, flowering and siliqua development stages according to crop requirement. One hand weeding followed by hoeing was carried out during early growth, and need-based plant protection measures were adopted against insect pests and diseases.

Observations and statistical analysis

Five plants were randomly selected and tagged from each net plot for recording growth and yield attributes. Plant population was recorded at 15 DAS and harvest. Plant height, branches plant⁻¹, dry matter accumulation and leaf area index were recorded at different crop stages. Yield attributes such as number of siliqua plant⁻¹, siliqua length, seeds siliqua⁻¹ and test weight were recorded at harvest. Seed and stover yields were obtained from net plot harvest and converted to kg ha⁻¹. Oil content was determined by Soxhlet extraction, while nutrient contents and uptake were estimated by standard laboratory methods. Harvest index was calculated as the ratio of seed yield to biological yield (Donald and Hamblin, 1976) [5] . The data were statistically analyzed as per the procedure for randomized block design described by Gomez and Gomez (1984) [8] . Treatment means were compared using the critical difference (CD) at 5% level of significance wherever the F-test was significant. Economic returns were calculated from seed and stover value and prevailing input costs.

Results and Discussion

Effect on soil properties and available nutrients after harvest Soil pH, electrical conductivity and organic carbon were not significantly affected by sulphur sources and levels, although small numerical shifts were observed. Soil pH decreased slightly from 7.55 in the control to 7.43 under T 10 , which may be associated with oxidation of sulphur and release of hydrogen ions. Electrical conductivity remained within the safe range for mustard growth. Organic carbon varied narrowly from 0.43 to 0.49%, indicating that short-term mineral fertilization did not cause a marked change in soil organic matter. Available N, P and S after harvest improved with sulphur application. T 10 recorded the highest available N (212.40 kg ha⁻¹), P (22.30 kg ha⁻¹) and S (20.20 kg ha⁻¹), while the control recorded the lowest values. Available K showed only numerical variation and remained non-significant, probably because the initial potassium status of the soil was adequate. Better nutrient availability under sulphur treatments may be due to improved root growth, mild acidifying effect of sulphur oxidation and sustained sulphate supply from bentonite. Similar improvements in soil nutrient availability and sulphur uptake with sulphur fertilization were reported by Chattopadhyay and Ghosh (2012) [3] , Jena et al. (2021) [12] and Dubey et al. (2022) [6] .

Effect on growth and phenology

Growth characters improved consistently with sulphur application. At harvest, maximum plant height (166.80 cm), branches plant⁻¹ (8.10) and dry matter accumulation (87.50 g plant⁻¹) were recorded under T 10 . The same treatment also recorded the highest LAI at 90 DAS (6.02) and at harvest (4.55). The improvement was mainly due to better nutrient absorption, enhanced chlorophyll synthesis and greater photosynthetic surface under adequate sulphur nutrition. T 10 was statistically at par with T 9 , T 8 and selected higher-sulphur treatments for several growth traits, showing that the response was strongest when balanced NPK was combined with higher sulphur supply. Days to 50% flowering decreased from 51.20 days in the control to 46.40 days under T 10 . Earlier flowering under sulphur nutrition may be linked with better vegetative vigor and timely transition from vegetative to reproductive growth. Similar beneficial effects of sulphur sources on plant height, leaf area development, branches and dry matter production have been observed by Kumar et al. (2015) [15] , Kumar et al. (2017) [17] , Singh et al. (2021) [23] and Jena et al. (2021) [12] .

Effect on yield attributes and yield

Yield attributes followed the same trend as growth characters. The application of 100% RDF + bentonite @ 60 kg S ha⁻¹ recorded the highest number of siliqua plant⁻¹ (312.00), siliqua length (5.78 cm), seeds siliqua⁻¹ (16.10) and test weight (5.32 g). These values were substantially higher than the control, which recorded 198.00 siliqua plant⁻¹, 4.10 cm siliqua length, 11.60 seeds siliqua⁻¹ and 4.12 g test weight. The improvement in reproductive characters can be attributed to better assimilate production, higher dry matter partitioning and sustained sulphur supply during flowering and siliqua development. Seed yield increased significantly with sulphur application. T 10 recorded the highest seed yield (1942 kg ha⁻¹), stover yield (5795 kg ha⁻¹) and biological yield (7737 kg ha⁻¹), representing a 53.5% increase in seed yield over the absolute control. T 10 was statistically at par with T 9 , T 8 and T 7 for seed yield, but it remained numerically superior. Harvest index did not show a significant response, suggesting that sulphur improved total biomass and seed production in a nearly proportional manner. These findings agree with Kumar and Trivedi (2012) [16] , Tiwari et al. (2021) [27] , Chauhan et al. (2022) [4] and Solanki et al. (2022) [25] , who reported higher seed yield and yield attributes of mustard with improved sulphur nutrition. Effect on nutrient uptake and oil content Sulphur application enhanced nutrient concentration and total nutrient uptake by the crop. T 10 recorded the highest seed sulphur content (0.85%), stover sulphur content (0.36%) and total uptake of N (118.78 kg ha⁻¹), P (21.68 kg ha⁻¹), K (106.70 kg ha⁻¹) and S (37.37 kg ha⁻¹). The higher uptake was mainly due to higher biomass and improved nutrient concentration in plant parts. Sulphur is closely associated with nitrogen metabolism and protein synthesis; therefore, balanced sulphur nutrition can improve the efficiency of applied NPK fertilizers. Oil content increased from 37.30% under the control to 42.30% under T 10 . The improvement in oil content under sulphur fertilization is expected because sulphur participates in oil biosynthesis and glucosinolate metabolism in Brassica crops. These results are in line with Falk et al. (2007) [7] , Singh et al. (2015) [24] , Dubey et al. (2022) [6] and Sharma et al. (2023) [22] , who reported enhancement in oil quality and nutrient uptake of mustard with adequate sulphur supply.

Effect on economics

Economic analysis showed that the increase in yield under sulphur fertilization compensated for the added cost of sulphur sources. The highest cost of cultivation was observed under T 10 (₹52,000 ha⁻¹), but this treatment also produced the maximum gross return (₹132,934 ha⁻¹), net return (₹80,934 ha⁻¹) and B:C ratio (2.56). T 9 and T 8 were the next best treatments with B:C ratios of 2.52 and 2.51, respectively. The lower B:C ratio under gypsum treatments at lower sulphur levels reflected smaller yield advantage in relation to cost. Similar economic superiority of higher-yielding sulphur treatments has been reported by Kumar and Trivedi (2012) [16] , Kushwaha et al. (2020) [18] , Chauhan et al. (2022) [4] and Solanki et al. (2022) [25] .

Conclusion

The study confirmed that Indian mustard responded positively to sulphur application under the sandy loam soil conditions of Gwalior. Application of sulphur with the recommended NPK dose improved growth, yield attributes, seed yield, oil content, nutrient uptake and profitability over the absolute control. Among the evaluated treatments, 100% RDF + bentonite @ 60 kg S ha⁻¹ was the most productive and remunerative treatment. It recorded the highest seed yield (1942 kg ha⁻¹), oil content (42.30%), total sulphur uptake (37.37 kg ha⁻¹), net return (₹80,934 ha⁻¹) and B:C ratio (2.56). The treatment was followed by 100% RDF + bentonite @ 50 kg S ha⁻¹ and 100% RDF + bentonite @ 40 kg S ha⁻¹.

On the basis of one-season field results, application of bentonite sulphur at 60 kg S ha⁻¹ along with 100% RDF can be recommended for improving productivity, quality and economic return of Indian mustard in sulphur-deficient sandy loam soils. Multi-season validation under different soil conditions may further refine the recommendation.

Acknowledgement

AcknowledgementThe authors acknowledge the School of Natural & Applied Sciences, Vikrant University, Gwalior, for providing field and laboratory facilities to conduct the experiment.

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