AB It is important to breed maize (Zea mays L) cultivars with high performance under variable N levels. We studied the effect of N levels and estimated quantitative genetic parameters for grain yield, quality, and other traits, and examined stability of performance for grain yield in diverse Chinese maize germplasm. From 2006 to 2008, each year 20 and in total 30 maize hybrids, including commercial hybrids currently grown in this region and other ex¬perimental hybrids as well as high-oil hybrids, were tested using nine environments (location-year combinations) in North China Plain. In each environment, two replicated trials were grown: one under high N application rate (HN, 225 kg N ha-1) and the other under low N application rate (LN, no N fertilization). Compared to HN, grain yield was significantly reduced (35.6%) under LN level, as well as kernel number per ear, 1000-kernel weight, plant and ear heights, and protein concentration. In the analysis over environments under each N level, genotypic variance was significant and heritability was high for all traits. In the analyses across N levels and environments, genotypic variance was significant for all traits and larger than the genotype × N and/or environment interaction variance components except for protein concentration. In stability analyses across N levels, hybrids differed for their linear response to environments, and some showed dissimilar response under HN and LN levels. Our results indicated that breeding maize adapted to variable N levels is feasible with the Chinese germplasm available in the summer breeding programs in North China Plain. Multi-environment tests are required to identify hybrids with high grain yield under variable N conditions, and examining yield stability separately under HN and LN would be useful
