Performance evaluation of short-duration chickpea varieties under late-sown conditions

Introduction

Across Iran's central plateau, chickpea planting is frequently delayed beyond the optimum October window because the preceding rice or maize crop hasn't been harvested in time [1] . Every week of delay exposes the reproductive phase to rising spring temperatures, which accelerate senescence and force the crop into premature maturity [2] . Yield losses of 30-60% have been reported from late sowing in comparable Mediterranean-type climates, yet many farmers have no practical alternative because double-cropping is the only way to make their small holdings economically viable [3,4] . Short-duration chickpea varieties, which mature in 100-120 days compared with 140-160 days for standard types, were bred specifically to escape terminal heat and drought [5] . Their compact growth habit and determinate flowering pattern allow them to set and fill pods before temperatures exceed the 35 °C threshold that damages pollen viability [6] . But not all shortduration lines perform equally when sowing is delayed some lose yield more steeply than others because they partition fewer assimilates to grain under truncated growing seasons [7] . This research compared five kabuli-type chickpea varieties at three sowing dates to identify the genotype that best tolerates late planting on the semi-arid outskirts of Tehran. Yield, yield components, phenology, and harvest index were measured to separate the effects of shorter crop duration from those of heat stress during grain filling [8,9,10] .

Soil characteristics

The trial site at the Karaj Research Station (35.82° N, 50.97° E, elevation 1,312 m) sits on a calcareous silt loam with 22% clay, 54% silt, and 24% sand. Topsoil pH was 7.8, organic carbon 0.78%, total N 0.07%, Olsen P 11.4 mg kg⁻¹, and exchangeable K 218 mg kg⁻¹. The soil is classified as a Typic Calcixerept. Field capacity at 0-30 cm was 28.3% (w/w) and permanent wilting point 13.1%. Irrigation water from the Karaj River diversion had EC 0.82 dS m⁻¹ and pH 7.3 [11] .

Seasonal weather conditions

Cumulative rainfall from October 2022 to May 2023 was 241 mm, close to the long-term average of 253 mm. Mean daily temperatures during the reproductive window (March-April) were 14.8 °C for the normal sowing and 19.6 °C for the very late sowing, reflecting how delayed planting pushed pod filling into warmer weeks. Maximum temperature exceeded 32 °C on 11 days during April for the very late treatment but on only 3 days for the normal sowing. These thermal differences account for much of the yield gap between sowing dates.

Material and Methods

Material

Five kabuli chickpea varieties were tested: Flip 09-40C, Arman, Azad, Hashem, and ILC 482. Seed was sourced from the Seed and Plant Improvement Institute, Karaj. All varieties are classified as short-duration (< 130 days under normal sowing) and are recommended for the Tehran province [5] . Before sowing, seeds were treated with Rhizobium ciceri inoculant and thiram fungicide at 2 g kg⁻¹ seed. Basal fertiliser was applied at 20 kg N and 40 kg P₂O₅ ha⁻¹ using diammonium phosphate [8] .

Methods

Three sowing dates were used: D1 (25 October 2022, normal), D2 (15 November 2022, late), and D3 (5 December 2022, very late). The experiment followed a split-plot design with sowing date as the main plot and variety as the subplot, replicated three times. Each subplot measured 4 m × 3 m with 30 cm row spacing and 10 cm plant spacing. Two supplemental irrigations were applied at flowering and pod filling when cumulative rainfall was insufficient. At maturity, a 2 m² area per subplot was harvested; pods per plant, seeds per pod, 100-seed weight, grain yield, biological yield, and harvest index were recorded. Growing Degree Days (GDD) were accumulated using a base temperature of 5 °C [6] . Data were analysed by split-plot ANOVA in SAS 9.4 with Tukey's HSD at p=0.05.

Field experimental design

The split-plot design assigned sowing dates to main plots and varieties to subplots within three complete blocks. Main plots were separated by 2-m alleys to prevent shading effects between sowing dates. Border rows surrounded each subplot. Phenological observations (days to 50% flowering, days to maturity) were recorded on five tagged plants per subplot. Thermal time from sowing to maturity was calculated by summing daily GDD.

Results

Comprehensive interpretation

The data consistently identify Hashem as the most resilient variety. Its combination of early flowering, high harvest index, and stable seed weight across sowing dates suggests that it partitions assimilates to grain more effectively than competing varieties when the growing season is cut short. ILC 482, by contrast, showed the steepest decline in every measured trait, likely because its slightly longer duration pushed grain filling into the hottest part of the season.

Discussion

The 43.8% mean yield reduction from normal to very late sowing agrees with losses reported from similar Mediterranean environments in Turkey and Morocco [3,4] . The mechanism is straightforward: delayed sowing shortens the vegetative phase, reduces canopy size, and pushes the critical flowering-to-pod-fill window into warmer weeks when pollen viability and assimilate supply both decline [2,6] . Hashem's advantage appears rooted in its ability to maintain a high harvest index (0.41) even under the most compressed season. While other varieties redirected assimilates toward vegetative survival producing taller plants with more branches but fewer filled pods Hashem kept its determinate habit and channelled carbon into seeds [7] . Its 100-seed weight dropped by only 8.0% from D1 to D3, compared with 16.3% for ILC 482, indicating better grain filling under heat.

The thermal time analysis adds nuance. Very late sown crops accumulated only 1,083 GDD versus 1,487 GDD for normal sowing. The 27.2% reduction in thermal units maps closely onto the 43.8% yield loss, suggesting that each degree-day lost costs roughly 1.6% of potential yield. Breeders could use this ratio to set realistic yield targets for late-planted chickpea across the Iranian plateau [9] . A limitation of this single-season trial is that rainfall timing differed from the long-term pattern; multi-year data would strengthen the variety recommendations.

Conclusion

References

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