Maize can be sown in spring and fall seasons in Pakistan under maize–maize cropping system. Due to seasonal variability in meteorological parameters, optimization of planting time for maize hybrids is vital to harvest improved productivity in maize-maize system. This study was designed to explore the effect of diverse sowing dates on phenology, growing degree days (GDDs), photo-thermal-units (PTUs) and helio-thermal-units (HTUs), and its impact on radiation-use-efficiency (RUE) and grain yield (GY) in different maize hybrids under maize-maize cropping system. Two-year experiments were conducted to optimize planting dates for hybrids during 2016 and 2017. In spring, three hybrids were sown on Jan 15, Feb 5, Feb 25, Mar 15 and Apr 05. During fall, three hybrids were planted on Jun 15, Jul 05, Jul 25, Aug 15 and Sept 05. Results showed that spring early (Jan 15), while fall late (Jul 25) sowing took more days to complete 50% tasseling, silking and maturity. However, maize sown on Feb 05 and Jul 25 accumulated more GDDs to attain 50% tasseling, silking and maturity. Maize sown on Feb 05 and Jul 25 had more leaf area index (LAI), crop growth rate (CGR), RUE and GY, which was linked with higher accrual of GDDs, PTUs and HTUs. Likewise, hybrids P-33M15 and P-30R50, during spring and fall observed higher values of all above cited traits. Moreover, positive-correlation was witnessed among days taken to complete different phenophases, LAI, CGR and 1000-grain weight, total biomass, GY and RUE. However, higher GY and RUE was obtained in spring than fall. In conclusion, maize sown on Feb 05 and Jul 25 using hybrids P-33M15 and P-30R50, during spring and fall crops, respectively produced more GY and higher RUE due to more accumulation of GDDs, PTUs and HTUs. Thus the spring season seemed more productive than fall season under maize-maize cropping system.

中文翻译：

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玉米-玉米系统的播种日期和杂交选择很重要

在玉米 - 玉米种植系统下，可以在巴基斯坦的春季和秋季播种玉米。由于气象参数的季节性变化，优化玉米杂交种的种植时间对于提高玉米-玉米系统的生产力至关重要。本研究旨在探讨不同播种日期对物候、生长度日 (GDD)、光热单位 (PTU) 和日光热单位 (HTU) 的影响，及其对辐射利用效率的影响。玉米-玉米种植制度下不同玉米杂交种的 RUE) 和籽粒产量 (GY)。进行了为期两年的试验，以优化 2016 年和 2017 年的杂交种种植日期。春季，1 月 15 日、2 月 5 日、2 月 25 日、3 月 15 日和 4 月 5 日播种了 3 个杂交种。秋季，6 月 15 日种植了 3 个杂交种、7 月 5 日、7 月 25 日、8 月 15 日和 9 月 5 日。结果表明，春季早（1 月 15 日）播种，而秋季晚（7 月 25 日）播种需要更多天数才能完成 50% 的抽穗、抽丝和成熟。然而，2 月 5 日和 7 月 25 日播种的玉米积累了更多的 GDD，达到 50% 的雄穗、脱丝和成熟。2 月 5 日和 7 月 25 日播种的玉米具有更高的叶面积指数 (LAI)、作物生长率 (CGR)、RUE 和 GY，这与更高的 GDD、PTU 和 HTU 应计有关。同样，在春季和秋季，杂种 P-33M15 和 P-30R50 观察到上述所有性状的较高值。此外，完成不同物候期所需的天数、LAI、CGR 和千粒重、总生物量、GY 和 RUE 之间存在正相关关系。然而，春季获得的 GY 和 RUE 高于秋季。总之，2 月 5 日和 7 月 25 日使用杂交种 P-33M15 和 P-30R50 在春季和秋季作物播种的玉米，由于更多的 GDD、PTU 和 HTU 的积累，分别产生了更多的 GY 和更高的 RUE。因此，在玉米-玉米种植制度下，春季似乎比秋季更有生产力。