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The optimum dose of fertilizers for crops varies with soil, agro-ecology, and crop management practices. Optimizing application dose is critical to reduce nutrient loss to the environment and increase nitrogen use efficiency (NUE), crop yields, and economic return to farmers. An experiment was conducted to determine the optimum N dose for increasing maize (Zea mays L. cv, Manakamana-3) yield, NUE, and farm profits under rainfed conditions. Five levels of N (0, 60, 120, 180, and 240 kg ha−1), and a non-fertilized treatment were tested in a randomized complete block design with three replications. Effects of each treatment on yield and yield attributing traits, plant lodging and Sterility (plants with no cob or grain formation), NUE, and stay green trait of maize were recorded. Application of N above 120 kg ha−1 (N120) did not have any significant effects on yield and yield components. Nitrogen, at N120 and above, produced highly fertile plants (though sterility slightly increased at N180 and N240), higher N uptake, and lower dead leaf area (18–27%). N120 produced the highest agronomic; yield increase per unit of N application (AEN—26.89 kg grain kg−1 N) and physiological efficiency of N (PEN—42.67 kg grain kg−1 N uptake), and net benefit (USD 500.43). Considering agronomic, economic, and NUE factors, an N dose of 120 kg ha−1 was found optimum for the cultivation of rainfed maize (Manakamana-3) under sandy loam soil.

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The present study was performed in a randomized complete block design with three replications to identify higher yielding genotypes and putative traits for grain yield improvement under a rainfed environment. Genotypes recorded highly significant variation for most of the observed agro-morphological traits except the number of effective tillers/m2. IR102774-31-21-2-4-7 (5.40 t/ha) followed by IR99739: 2-1-1-2-1 (5.22 t/ha), and IR103587-23-2-1-B (5.05 t/ha) respectively were the higher grain yielders. These high yielders were among the sets of early flowering (85-96 days) and maturing (120-130 days) genotypes. Plant height (PHT-86.62% and 25.69%), harvest index (HI-87.17% and 44.66%), and thousand-grain weight (TGW-71.06% and 30.05%) recorded high heritability values coupled with higher genetic advance as a percentage of the mean (GAM). IR102774-31-21-2-4-7 produced superior agro-morphological character for several traits like grain yield, thousand-grain weight, biological yield, plant height, and days to flowering and maturity. Plant height, biological yield, harvest index, days to flowering, and maturity were highly associated with grain yield and had medium to high heritability and GAM values. Therefore, these traits might be of importance for selection in grain yield improvement of rice under rainfed lowland conditions.