Effect of sowing dates and varieties on growth, yield, quality and economics of summer soybean (Glycine Max L.) under south Saurashtra conditions of Gujarat

Introduction

Soybean (Glycine max L.), the "miracle crop" of the 21 st century, is an industrially important oilseed-cum-pulse crop whose dry seed contains nearly 40 per cent protein and 20 per cent oil, along with dietary fibre, calcium, phosphorus, iron and B-complex vitamins (Hammond et al., 2005; Hou et al., 2009) [10,11] . It is also a rich source of polyunsaturated fatty acids and minerals, and its cultivation additionally builds soil fertility through symbiotic atmospheric nitrogen fixation (Devi et al., 2012) [7] . Global soybean production stood at 426.82 million tonnes during 2025-26, with five countries-the USA, Brazil, Argentina, China and India-together accounting for more than 87 per cent of world output (Anonymous, 2026a) [1] . India produced 12.50 million tonnes from 11.83 million hectares at a productivity of 1056 kg/ha, with Madhya Pradesh, Maharashtra, Rajasthan, Karnataka and Gujarat as the leading states (Anonymous, 2026b) [2] . Within Gujarat, the Saurashtra region leads soybean cultivation, and the state ranked fifth nationally with a production of 5.10 lakh tonnes and a productivity of about 1697 kg/ha during 2024-25, well above the national average (Anonymous, 2026c) [3] . Time of sowing is one of the most decisive agronomic factors governing soybean performance. Early planting can lengthen the reproductive phase and improve dry matter accumulation during seed filling, but sowing too early exposes the crop to low soil temperature and delayed germination, whereas delayed sowing curtails vegetative growth and compresses flowering and pod filling, with reported yield losses of 17 to 43 kg/ha for every day of delay beyond the optimum window. Photoperiod and temperature together regulate both the onset of flowering and the duration of vegetative growth in soybean, so that deviation from the optimum sowing window in either direction can compromise yield and grain quality (Berger et al., 2014) [5] . Variety selection is equally important; GJS-3 and GS-4 are recent high-yielding releases of Junagadh Agricultural University recommended for cultivation in Gujarat, and matching such varieties with the appropriate sowing window is essential for realising their full yield potential. Despite growing interest in summer soybean in the Saurashtra region, information on the most suitable sowing time and variety for this specific agroclimatic condition remains limited. The present investigation was therefore undertaken to study the effect of sowing dates and varieties, including their interaction, on the growth, yield attributes, yield, quality and economics of summer soybean under south Saurashtra conditions of Gujarat.

Materials and Methods

Experimental site, season and soil

A field experiment was conducted during the summer seasons of 2023 and 2024 at Sagadividi Farm, Department of Seed Science and Technology, College of Agriculture, Junagadh Agricultural University, Junagadh (21.5° N latitude, 70.5° E longitude, 60 m above mean sea level), which falls under the South Saurashtra Agro-climatic Zone of Gujarat. The soil of the experimental site was clayey in texture and mildly alkaline in reaction (pH 7.9-8.0, EC 0.52-0.57 dS/m), medium in organic carbon (0.63-0.68%) and in available phosphorus (24.6-26.7 kg/ha) and potassium (247-250 kg/ha), but low in available nitrogen (230-233 kg/ha).

Treatments and experimental design

The experiment comprised 12 treatment combinations of three sowing dates as the main-plot treatment-T1: 4 th week of January, T2: 2 nd week of February and T3: 4 th week of February-and four soybean varieties as the sub-plot treatment-V1: GJS-3, V2: GS-4, V3: NRC-138 and V4: Phule Sangam-laid out in a Split Plot Design with three replications (gross plot 5.0 m × 3.6 m; net plot 4.0 m × 2.7 m). Seed was sown at a rate of 60 kg/ha with a spacing of 45 cm × 10 cm, and a recommended dose of 30 kg N and 60 kg P2O5/ha was applied basally through urea and DAP. The crop received eight irrigations during its life span and was managed with recommended plant protection measures.

Observations recorded

Growth parameters, including initial and final plant population, plant height, and number of branches per plant, as well as yield attributes and yield parameters, including number of pods per plant, number of seeds per pod, test weight, seed yield, haulm yield, and harvest index, were recorded from five randomly selected and tagged plants in each net plot, following standard procedures. Dry weight per plant at 30 and 60 days after sowing (DAS) and at harvest, and the number of nodules per plant at 45 DAS, were recorded from the border rows on both sides of each plot. For dry weight estimation, five plants were collected at each sampling stage (30 DAS, 60 DAS, and maturity), sun-dried for two to three days, and subsequently oven-dried at 70°C until a constant weight was attained. The average dry weight was calculated and expressed as g/plant. Oil content was estimated on a dry-weight basis using nuclear magnetic resonance (NMR) spectrophotometry against a standard reference sample (Tiwari et al., 1974) [23] .. Protein content was estimated using the micro-Kjeldahl method, and the nitrogen content was converted to protein using a conversion factor of 6.25 (Gassi et al., 1973) [8] . The cost of cultivation, gross returns, net returns, and benefit-cost (B:C) ratio were calculated treatment-wise based on the prevailing market prices of the produce and inputs.

Statistical analysis

Data recorded during both years were statistically analysed separately and in pooled form following the analysis of variance technique for Split Plot Design as described by Gomez and Gomez (1984) [9] . Treatment means were compared using the critical difference (C.D.) at 5 per cent probability wherever the Ftest was significant; "NS" denotes a non-significant effect.

Results and Discussion

Plant population

Time of sowing had no significant effect on either initial or final plant population in 2023, 2024 or in pooled analysis (Table 1), indicating that seedling establishment was unaffected across the three sowing windows, probably because soil temperature during January-February (22-30°C) remained within the optimum range for soybean germination. Varietal differences were also nonsignificant, although GS-4 recorded the numerically highest final population (212610 plants/ha, pooled), followed by GJS-3 (207011), Phule Sangam (202645) and NRC-138 (195515). The T × V interaction and year effects were non-significant. These results corroborate the findings of Kaushik et al. (2014) [14] , Jaybhaye et al. (2015) [13] ., Naidu et al. (2016) [16] and Prabhakar et al. (2018) [18] .

Plant height

Time of sowing significantly influenced plant height at both 30 DAS and at harvest in both years and in pooled analysis (Table 1). The 4 th week of January produced the tallest plants at 30 DAS (22.07 cm, pooled) and at harvest (32.20 cm), significantly taller than the 2 nd week of February (19.78 and 29.72 cm) and the 4 th week of February (17.94 and 27.99 cm), with a consistent decline as sowing was delayed. Among varieties, GS-4 (21.52 cm at 30 DAS; 31.72 cm at harvest) remained at par with GJS-3 and was significantly taller than NRC-138, the shortest variety at both stages. The T × V interaction and year effects were nonsignificant. The greater height under early sowing is attributable to the moderate temperature prevailing during the vegetative phase of January-sown crops, which favoured a longer period of internode elongation, whereas the rising temperature and photoperiod under late February sowing compressed the vegetative phase. The taller stature of GS-4 and GJS-3 reflects their inherently greater vegetative vigour. These findings agree with Rekha and Dhurua (2010) [20] , Hu and Wiatrak (2012) [12] ., Naidu et al. (2016) [16] , Nath et al. (2017) [17] . and Raghuwanshi et al. (2017) [19] . [22] , Jaybhaye et al. (2015) [13] ., Kaushik et al.

(2014) [14] , Naidu et al. (2016) [16] and Raghuwanshi et al. (2017) [19] . NS NS NS = Non-significant. Year (Y) and year × treatment interaction effects were non-significant for both traits.

Dry weight per plant

Dry weight per plant was significantly influenced by time of sowing at 30 DAS, 60 DAS and at harvest in both years and in pooled analysis (Table 3). The 2 nd week of February recorded the highest dry weight at 30 DAS (1.69 g, pooled), but by 60 DAS and at harvest the 4 th week of January took the lead (9.96 g and 16.16 g, respectively; at par with the 2 nd week of February at harvest), while the 4 th week of February recorded the lowest dry weight at all three stages owing to its shortened vegetative period. Among varieties, differences were non-significant at 30 DAS, but by 60 DAS Phule Sangam accumulated significantly more dry weight (11.36 g) than the rest, and at harvest GS-4 (15.63 g) and GJS-3 (15.53 g) were at par and significantly heavier than Phule Sangam and NRC-138, the last recording the lowest dry weight throughout. Interaction and year effects were non-significant at all stages. The early warmth of February favoured rapid initial growth, whereas the longer photosynthetically active period of January-sown crops translated into greater biomass by harvest. These findings agree with Kaushik et al. (2014) [14] , Singh et al. (2014) [22] , Naidu et al. (2016) [16] , Raghuwanshi et al. (2017) [19] . and Vadhavana (2026) [25] . -significant. Year (Y) and year × treatment interaction effects were non-significant at all three stages.

Number of pods per plant and number of seeds per pod

Time of sowing significantly influenced the number of pods per plant, with the 2 nd week of February recording significantly more pods (37.11, pooled) than the 4 th week of January (31.86) and the 4 th week of February (24.01), the last being the lowest (Table 4). Among varieties, GS-4 (33.86) remained at par with GJS-3 (32.03) and was significantly superior to Phule Sangam (29.26) and NRC-138 (28.82, the lowest). Number of seeds per pod, however, was not significantly affected by either sowing date or variety, indicating that this trait is governed more by genetic constitution than by sowing environment. Interaction effects were non-significant for both traits. The higher pod number under the 2 nd week of February reflects the favourable temperature and photoperiod combination available during flowering and pod set, whereas late sowing exposed the crop to rising temperature during this critical stage, increasing flower and pod abortion. These results agree with Kaushik et al. (2014) [14] ., Jaybhaye et al. (2015) [13] ., Naidu et al. (2016) [16] ., Kundu et al. (2016) [15] . and Raghuwanshi et al. (2017) [19] . NS NS NS = Non-significant. Year (Y) and year × treatment interaction effects were non-significant for both traits.

Test weight and harvest index

Test weight (100-seed weight) was not significantly influenced by time of sowing, though the 2 nd week of February recorded a marginally higher value (11.01 g, pooled) (Table 5). Varietal differences were significant, with GJS-3 recording the significantly highest test weight (12.05 g), followed by Phule Sangam (11.29 g), while GS-4 and NRC-138 were at par and lowest (10.33 and 10.22 g). Harvest index was not significantly affected by either sowing date or variety, with values ranging narrowly from 38.97 to 41.33 per cent across sowing dates and from 39.80 to 40.21 per cent across varieties, indicating that seed and haulm yield were altered proportionately under the different treatments. Interaction effects were non-significant for both traits. The stable test weight across sowing dates reflects a compensatory mechanism in soybean whereby a reduction in pod number is partly offset by maintenance of individual seed size, while the consistently heavier seed of GJS-3 reflects its genetic capacity for greater assimilate accumulation per seed. These findings agree with Kaushik et al. (2014) [14] ., Singh et al. (2014) [22] , Kundu et al. (2016) [15] , Raghuwanshi et al. (2017) [19] . and Prabhakar et al. (2018) [18] . -significant. Year (Y) and year × treatment interaction effects were non-significant for both traits.

Seed yield, haulm yield and their interaction with variety

Seed yield and haulm yield were significantly influenced by time of sowing, variety and their interaction in both years and in pooled analysis (Table 6). The 2 nd week of February recorded the significantly highest seed yield (1322 kg/ha, pooled) and haulm yield (1876 kg/ha, at par with the 4 th week of January), both significantly superior to the 4 th week of February (866 and 1355 kg/ha, respectively), the lowest for both traits. Among varieties, GS-4 (1238 kg/ha seed yield; 1838 kg/ha haulm yield) remained at par with GJS-3 (1225 and 1816 kg/ha) and was significantly superior to Phule Sangam and NRC-138, the last recording the lowest yield of both. The T × V interaction was significant for both traits (Tables 7 and8): the combination of 2 nd week of February × GS-4 recorded the significantly highest seed yield (1358 kg/ha, pooled; at par with T2V1, T2V4 and T2V3) and haulm yield (1916 kg/ha, at par with T2V1, T1V2 and T1V1), while the 4 th week of February × NRC-138 recorded the lowest seed yield (605 kg/ha) and haulm yield (956 kg/ha). The superior yield under the 2 nd week of February reflects the greater pod number and favourable temperature during reproductive growth that enhanced photosynthate translocation to the developing seed, whereas the longer vegetative duration of January-and February-sown crops favoured greater haulm accumulation; delayed sowing under the 4 th week of February shortened both phases and curtailed yield. These findings agree with Kaushik et al. (2014) [14] ., Jaybhaye et al. (2015) [13] , Naidu et al. (2016) [16] ., Kundu et al. (2016) [15] , Raghuwanshi et al. (2017) [19] ., Dakhore et al. (2024) [6] . and Vadhavana (2026) [25] . NS NS NS = Non-significant. Year (Y) and year × treatment interaction effects were non-significant for both traits.

Economics

Economic analysis based on the mean of both years showed that the 2 nd week of February recorded the highest gross returns (₹97,230/ha), net returns (₹44,720/ha) and benefit-cost ratio (1.85), followed by the 4th week of January (₹90,610, ₹37,734/ha and 1.71); the 4 th week of February was the least remunerative (₹64,008, ₹11,498/ha and 1.22) despite an almost identical cost of cultivation to the 2 nd week of February (Table 10). Among varieties, GS-4 gave the highest net returns (₹38,562/ha) and B:C ratio (1.73), closely followed by GJS-3 (₹37,597/ha; 1.71), while NRC-138 was the least profitable (₹22,240/ha; 1.42) despite a uniform cost of cultivation (₹52,693/ha) across varieties. The superior economic performance of the 2 nd week of February and of GS-4/GJS-3 tracked their higher seed yield, confirming that both the choice of sowing time and variety are decisive for the profitability of summer soybean cultivation in this region. These findings corroborate Kaushik et al. (2014) [14] ., Tomar et al. (2014) [24] ., Jaybhaye et al. (2015) [13] . and Naidu et al. (2016) [16] ..

Conclusion

Based on the two-year field experiment, sowing summer soybean in the 2 nd week of February, combined with the variety GS-4, consistently produced the best combination of pod number, seed yield, haulm yield and economic return, and the interaction of the 2 nd week of February × GS-4 gave the single highest seed and haulm yield among all treatment combinations. NRC-138, while the lowest yielding, was distinguished by significantly higher seed protein content and may be considered where quality rather than yield is the priority. For higher productivity and profitability of summer soybean under south Saurashtra conditions of Gujarat, sowing in the 2 nd week of February with variety GS-4 is advisable.

Acknowledgement

AcknowledgementThe authors are grateful to the Department of Seed Science and Technology and Department of Agronomy, Junagadh Agricultural University, Junagadh, for providing the experimental site and facilities used in this study.

References

1. ±, C.D. at 5% and CV (%) values apply to the T × V interaction within each year/pooled column-group (2023, 2024, Pooled respectively).
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