Optimization of sowing time and plant population for maximizing sesame (Sesamum indicum) productivity

Introduction

Low and unstable yields remain the single biggest obstacle to expanding sesame (Sesamum indicum L.) cultivation in southern Europe. While global demand for sesame seed has risen by 4.7% annually over the past decade [7] , European production covers less than 0.3% of world output, partly because agronomic recommendations developed for tropical and subtropical environments don't transfer well to Mediterranean climates [3] . Sowing too early exposes seedlings to suboptimal soil temperatures below 18 °C, while late sowing shortens the growing season and delays maturity into autumn rains [1,5] . Plant population interacts strongly with sowing date because the duration of vegetative growth determines the branching window available for capsule formation [2] . At low densities, sesame compensates through increased branching and capsule number per plant, but total yield per hectare may suffer from underutilized light interception [4] . At high densities, inter-plant competition reduces branching and individual plant yield, though the population effect can offset this if the optimum is matched to the sowing date [15] . Noorka et al. [4] found that 35-45 plants/m² maximized yield in Pakistan, while Subrahmaniyan et al. [15] reported 40 plants/m² as optimal under Indian rainfed conditions. No factorial evaluation of sowing time and plant population has been conducted for sesame in the Mediterranean basin. This research aimed to identify the sowing date and population combination that maximizes seed yield and oil content under the warm temperate conditions of northern Italy, and to determine whether significant interactions between these two factors affect yield component expression.

Materials and Methods

Field experimental design

The experiment was a 5 × 4 factorial arranged in a randomized complete block design with three replications. Main factors were sowing date ( Populations were achieved by adjusting within-row spacing while keeping row spacing constant at 40 cm [9] .

Seasonal variations

In 2021, cumulative rainfall from March to September was 412 mm with mean temperature of 21.3 °C. The 2022 season was warmer (mean 22.8 °C) and drier (347 mm), with a 19-day rainless period in July. Despite year differences, the sowing date × population interaction patterns were consistent, so data were pooled after confirming homogeneity of variances by Bartlett's test.

Material

Sesame variety Padma, a non-shattering type adapted to mechanized harvest, was used. Seeds were treated with metalaxyl-M (0.3 g a.i./kg seed) before sowing. The soil was a Typic Udifluvent (silt loam, pH 7.4, organic matter 1.8%, available P 18.3 mg/kg, exchangeable K 164 mg/kg). Basal fertilization consisted of 40:60:40 kg N:P₂O₅:K₂O/ha, with an additional 30 kg N/ha side-dressed at the budding stage [10] .

Methods

At maturity, five plants per plot were sampled to measure capsules per plant, seeds per capsule, and 1000-seed weight. Seed yield was determined from a central 4 m² harvest area adjusted to 6% moisture. Oil content was measured by Soxhlet extraction with petroleum ether. Data were analyzed by factorial ANOVA in R 4.2, means separated by Tukey HSD at p≤0.05 [9] .

Results

Comprehensive interpretation

The sowing date × plant population interaction was significant (p<0.01) for seed yield. The 15 April sowing at 40 plants/m² produced the peak yield of 1,124 kg/ha (Table 1, Figure 1), 63.6% higher than the 15 March × 20 plants/m² combination. Within each sowing date, 40 plants/m² consistently outyielded other densities. All yield components peaked with 15 April sowing: 48.2 capsules/plant, 63.7 seeds/capsule, and 3.52 g test weight (Table 2, Figure 2). Oil content was statistically uniform across sowing dates (46.8-48.3%) but showed a non-significant trend toward lower values at 50 plants/m².

Discussion

The 15 April sowing aligned sesame's thermophilic requirements with optimal soil and air temperatures in the Emilia-Romagna plain. Earlier sowings (15 March) suffered from slow emergence due to soil temperatures below 18 °C, delaying canopy closure and reducing the effective capsule-bearing period [1,5] . Later sowings (1 and 15 May) truncated the reproductive phase, as declining photoperiod and autumn rains interfered with capsule maturation and drying [3] . The superiority of 40 plants/m² reflects an optimal balance between individual plant productivity and population-level resource capture. At 20 plants/m², excessive branching diluted assimilates across too many capsules, reducing seed fill. At 50 plants/m², competition suppressed branching and capsule number without a compensating increase in total yield [4,15] . The stability of oil content across treatments suggests that seed composition is under stronger genetic than environmental control in this cultivar, consistent with Uzun et al. [8] .

Conclusion

References

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