Maize is sown during spring and autumn seasons in Pakistan; however, studies on inter-seasonal variability on maize productivity, agronomic and nitrogen use efficiencies (NUEs) are limited. Therefore optimization of nitrogen (N) rate and hybrids selection for each season is critical to harvest better yield in maize–maize cropping system. Two independent field experiments were conducted to optimize N rates for different hybrids to improve maize productivity and NUEs in spring and autumn seasons during 2016 and 2017. During spring season, three spring-hybrids (P-33M15, M-DK6525 and S-NK8441) and during autumn season, three autumn-hybrids (P-30R50, M-DK6714 and S-NK6621) were sown under five N levels i.e., 0, 80, 160, 240 and 320 kg ha −1 . Maize yield and related traits, and NUEs were improved with each higher level of N application. Highest and lowest grain yield, agronomic and economic NUEs were recorded at 320 kg N ha −1 and without N application, respectively in both seasons. Likewise, highest grain yield and NUEs were observed by spring-hybrid P-33M15 and autumn-hybrid P-30R50, while lowest were obtained by spring hybrid S-NK8441 and autumn hybrid S-NK6621 during both years. Nonetheless, maximum net income and benefit: cost ratio was observed by spring-hybrid P-33M15 and autumn-hybrid P-30R50 at higher N level (320 kg ha −1 ) and maize cultivation without N was not profitable in both seasons. Maize cultivation with N application at 320 kg ha −1 seemed a viable option to get maximum productivity, economic returns and NUEs of maize–maize cropping system in irrigated arid environment of southern Punjab, Pakistan and might be for other areas having similar environmental conditions.

中文翻译：

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氮肥率和杂交选择对巴基斯坦旁遮普省南部灌溉干旱环境下玉米-玉米种植系统的生产力至关重要

玉米在巴基斯坦春秋两季播种；然而，关于玉米生产力、农艺和氮肥利用效率 (NUE) 的季节性变化的研究是有限的。因此，优化每个季节的氮 (N) 率和杂交种选择对于在玉米 - 玉米种植系统中获得更高的产量至关重要。在 2016 年和 2017 年春季和秋季，进行了两个独立的田间试验以优化不同杂交种的氮肥量，以提高玉米生产力和 NUE。在春季，三个春季杂交种（P-33M15、M-DK6525 和 S-NK8441）在秋季，三个秋季杂交种（P-30R50、M-DK6714 和 S-NK6621）在五个 N 水平下播种，即 0、80、160、240 和 320 kg ha -1 。随着施氮水平的提高，玉米产量和相关性状以及 NUE 得到改善。两个季节分别在 320 kg N ha -1 和不施氮时记录了最高和最低的谷物产量、农艺和经济 NUE。同样，春季杂交 P-33M15 和秋季杂交 P-30R50 的籽粒产量和 NUE 最高，而春季杂交 S-NK8441 和秋季杂交 S-NK6621 的产量和 NUE 最低。尽管如此，春季杂交 P-33M15 和秋季杂交 P-30R50 在较高的氮水平（320 kg ha -1 ）下观察到最大的净收入和收益：成本比，并且没有 N 的玉米种植在两个季节都没有盈利。在旁遮普邦南部灌溉干旱环境中，以 320 kg ha -1 施氮的玉米种植似乎是获得最大生产力、经济回报和玉米 - 玉米种植系统的 NUE 的可行选择，