Document Type : Research Article
Authors
1
Department of Agronomy, Ahv. C., Islamic Azad University, Ahvaz, Iran
2
Agricultural and Horticultural Sciences, Department of Agricultural and Natural Resources
10.22067/jcesc.2026.98388.1454
Abstract
Introduction
In tropical and subtropical regions, sustainable increases in production face serious climatic challenges. In this context, summer-winter cropping system has been proposed as management strategy to optimize the use of land and limited water resources. The summer crop (late season) confronts high soil temperatures at germination, which can affect uniform establishment. Conversely, this heat can lead to higher vegetative growth rates and a shortened growth cycle, provided the plant escapes peak summer heat, creating a time window for the second crop. The subsequent winter crop then faces low temperatures during early growth stages, which can reduce field emergence and establishment. Following this, with rapid spring warming, the plant is forced to cope with terminal heat stress during sensitive reproductive and grain-filling stages. This end-of-season stress can severely disrupt key physiological processes such as current photosynthesis, assimilate partitioning, and grain filling, ultimately reducing yield components. This study was designed to evaluate the feasibility of a sequential cycle bread wheat system.
Materials and Methods
The experiment was conducted as a split-plot arrangement in a randomized complete block design with three replications over two cropping years (2022–2023 and 2023–2024) in the Shavor region of Khuzestan. The factors included four sowing dates for the first (summer) crop: 11 September, 21 September, 1 October and 11 October, and four bread wheat cultivars: Mehregan, Chamran-2, Aineh and Sareng. Following the complete harvest of the summer crop, the field was re-prepared and the winter crop was sown with the same cultivars on sequentially aligned dates: 25 December, 30 December, 10 January, and 31 January, respectively, maintaining the cropping sequence for each initial sowing date. Measurements included emergence percentage, spike number per m², grains per spike, one-thousand kernel weight, grain yield, chlorophyll a, b and total chlorophyll content, current net photosynthesis rate and dry matter remobilization. Data from the two years were combined and analyzed using composite analysis of variance. Mean comparisons were performed using Duncan's Multiple Range Test at the 5% probability level.
Results and Discussion
The analysis revealed that sowing date and cultivar and their interaction significantly affected most measured traits. The latest sowing dates (1 Oct/31 Jan and 11 Oct/5 Feb), which avoided peak temperature stresses during germination of both cycles, generally created more favorable physiological conditions. For emergence, cultivar Sareng under 1 Oct/31 Jan showed the highest summer–winter mean (79.86%), while Chamran-2 under the earliest sowing (11 Sep/15 Jan) had the lowest (56.76%), linking poor establishment to high soil temperatures at early sowing. Regarding spike number per m² was highest for Aineh under 11 Sep/15 Jan (354.85) due to a longer vegetative period under moderate autumn temperatures, but lowest for Mehregan under 11 Oct/5 Feb (242.67). Sareng under 11 Oct/5 Feb had the highest summer–winter mean (30.92 grains per spike), while Aineh under 11 Sep/15 Jan had the lowest (25.24), suggesting resource reallocation to maximize grain set in existing sinks when tillering was limited. One-Thousand Kernel Weight was highest for Sareng under 1 Oct/31 Jan (40.98 g) and lowest for Aineh under 11 Sep/15 Jan (34.73 g). The highest summer–winter mean yield (1408.1 kg ha⁻¹) was achieved by the early-maturing, stress-tolerant cultivar Mehregan under the latest sowing (11 Oct/5 Feb), successfully implementing a "stress escape" strategy. In stark contrast, the longer-duration cultivar Chamran-2 under the same 11 Oct/5 Feb recorded the lowest yield (1203.58 kg ha⁻¹), as its extended cycle forced it to endure critical reproductive stages during periods of heat stress. Mehregan under 11 Oct/5 Feb also had the highest total chlorophyll (1.359 mg/g FW) and the highest current net photosynthesis in the mean of two crops (73.94 g/m²), with strong positive correlations to yield, indicating maintained photosynthetic capacity was key to success. Furthermore, dry matter remobilization played a vital compensatory role; Chamran-2 under 11 Oct/5 Feb showed the highest remobilization in the mean of two crops (59.05 g/m²), suggesting greater reliance on stored reserves when current photosynthesis was potentially limited.
Conclusion
This study demonstrates that implementing a summer-winter wheat cropping system in hot, dry regions is feasible, contingent upon intelligent management of sowing date and cultivar selection. Intermediate to late sowing dates (1 Oct/31 Jan and 11 Oct/5 Feb), which avoided peak stresses, generally created more favorable conditions. Among cultivars, the early-maturing, stress-adapted Mehregan, sown late (11 Oct/5 Feb), achieved the highest summer–winter mean yield (1408 kg ha⁻¹), chlorophyll content, and photosynthetic rate, confirming the success of a "stress escape" strategy. In contrast, longer-duration cultivars like Chamran-2 were severely damaged under inappropriate (especially late) sowing dates. The role of efficient remobilization as a compensatory mechanism for maintaining grain weight under terminal heat stress was confirmed. Overall, success in this double-cropping system hinges on the precise matching of cultivar phenological traits (especially growth duration) with the regional pattern of temperature stresses through optimal sowing date selection.
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